View and query VM metadata

Every virtual machine (VM) stores its metadata in directories on a metadata server. Your VM automatically has access to this metadata server API without any additional authorization. You can use the methods explained in the following sections of this document to view and query VM metadata values:

If you encounter errors when accessing the metadata server, review Troubleshooting metadata server access issues.

Before you begin

  • For Windows Server VMs, use PowerShell 3.0 or later. We recommend that you use ctrl+v to paste the copied code blocks.
  • Review the basics of how VM metadata for Compute Engine is defined, categorized, and arranged. For more information, see About VM metadata.
  • If you haven't already, then set up authentication. Authentication is the process by which your identity is verified for access to Google Cloud services and APIs. To run code or samples from a local development environment, you can authenticate to Compute Engine by selecting one of the following options:

    Select the tab for how you plan to use the samples on this page:

    Console

    When you use the Google Cloud console to access Google Cloud services and APIs, you don't need to set up authentication.

    gcloud

    1. Install the Google Cloud CLI, then initialize it by running the following command: 

      gcloud init
    2. Set a default region and zone.

    Python

    To use the Python samples on this page in a local development environment, install and initialize the gcloud CLI, and then set up Application Default Credentials with your user credentials.

    1. Install the Google Cloud CLI.

    2. To initialize the gcloud CLI, run the following command: 

      gcloud init

    3. If you're using a local shell, then create local authentication credentials for your user account: 

      gcloud auth application-default login

      You don't need to do this if you're using Cloud Shell.

    For more information, see Set up authentication for a local development environment.

    REST

    To use the REST API samples on this page in a local development environment, you use the credentials you provide to the gcloud CLI.

      Install the Google Cloud CLI, then initialize it by running the following command: 

      gcloud init

    For more information, see Authenticate for using REST in the Google Cloud authentication documentation.

Required roles

The following roles and permissions are needed to view custom metadata from outside the VM by using the Google Cloud console, the Google Cloud CLI, or REST. If you are programmatically querying the metadata from within the VM, you only need the roles and permissions for connecting to the VM.

To get the permissions that you need to view custom metadata from outside the VM, ask your administrator to grant you the following IAM roles:

For more information about granting roles, see Manage access to projects, folders, and organizations.

These predefined roles contain the permissions required to view custom metadata from outside the VM. To see the exact permissions that are required, expand the Required permissions section:

Required permissions

The following permissions are required to view custom metadata from outside the VM:

  • To view custom project metadata: compute.projects.get on the project
  • To view custom zonal metadata: compute.instanceSettings.get on the instance settings in the required zone in the project
  • To view custom metadata for a VM instance: compute.instances.get on the VM
  • If your VMs use service accounts: iam.serviceAccounts.actAs on the service accounts or project

You might also be able to get these permissions with custom roles or other predefined roles.

Programmatically query metadata

You can access all metadata by querying the metadata value entries programmatically from within a Linux or Windows VM. From within your VM, you can programmatically query your metadata values in one of the following ways by using tools such as curl on Linux or Invoke-RestMethod on Windows:

Metadata server endpoints

To programmatically query metadata, from within a VM, you have the following metadata server endpoints:

  • For all VMs, you can query the metadata server by using the http endpoint (http://metadata.google.internal/computeMetadata/v1).

  • For Shielded VMs, you can query the metadata server by using one of the following:

Most examples in this document use the http endpoint. However, you can access all the same metadata entries whether you use the https or the http endpoint.

Parts of a metadata request

The following table summarizes the main parts of a metadata query request.

Components Description
Root URLs

All metadata values are defined as sub-paths below the following root URLs:

  • http endpoint: 
    • http://metadata.google.internal/computeMetadata/v1
    • http://169.254.169.254/computeMetadata/v1
    • http://metadata.goog/computeMetadata/v1
  • https endpoint (Preview): 
    • https://metadata.google.internal/computeMetadata/v1
      This is the only supported URL during the preview stage.
Request header

This header indicates that the request was sent with the intention of retrieving metadata values, rather than unintentionally from an insecure source, and lets the metadata server return the data you requested. If you don't provide this header, the metadata server denies your request.

Metadata-Flavor: Google

Query a single metadata entry

Use the following commands to query a single metadata entry.

Linux

  1. Connect to your Linux VM.

  2. From your Linux VM, use the curl tool to make a query. To query for a VM instance or project metadata entry, run the following command:

    curl "http://metadata.google.internal/computeMetadata/v1/PATH_TO_METADATA_ENTRY" -H "Metadata-Flavor: Google"

    Replace the PATH_TO_METADATA_ENTRY with the path to the VM instance or project metadata key for which you want to query the value. If the key is in a sub-directory of the instance or project directory, ensure to also include the sub-directory. For example:

    • To view the project-id metadata key, which is stored in project metadata, specify project/project-id.
    • To view the image metadata key, which is stored in VM instance metadata, specify instance/image.
    • To view the enable-oslogin which can be stored in the attributes sub-directory of either project or VM instance metadata, specify either project/attributes/enable-oslogin or instance/attributes/enable-oslogin depending on your use case.

    For example, to query the boot image for the VM, run the following query:

    user@myinst:~$ curl "http://metadata.google.internal/computeMetadata/v1/instance/image" -H "Metadata-Flavor: Google"

    The output is similar to the following:

    projects/rhel-cloud/global/images/rhel-8-v20210122

Windows

  1. Connect to your Windows VM.

  2. From your Windows VM, use the Invoke-RestMethod command to make a query. To query for a VM instance or project metadata entry, run the following command:

    $value = (Invoke-RestMethod `
          -Headers @{'Metadata-Flavor' = 'Google'} `
          -Uri "http://metadata.google.internal/computeMetadata/v1/PATH_TO_METADATA_ENTRY")
$value

    Replace the PATH_TO_METADATA_ENTRY with the path to the VM instance or project metadata key for which you want to query the value. If the key is in a sub-directory of the instance or project directory, ensure to also include the sub-directory. For example:

    • To view the project-id metadata key, which is stored in project metadata, specify project/project-id.
    • To view the image metadata key, which is stored in VM instance metadata, specify instance/image.
    • To view the enable-oslogin which can be stored in the attributes sub-directory of either project or VM instance metadata, specify either project/attributes/enable-oslogin or instance/attributes/enable-oslogin depending on your use case.

    For example, to query the boot image for the VM, run the following query:

    PS C:\> 
$value = (Invoke-RestMethod `
          -Headers @{'Metadata-Flavor' = 'Google'} `
          -Uri "http://metadata.google.internal/computeMetadata/v1/instance/image")
$value

    The output is similar to the following:

    projects/windows-cloud/global/images/windows-server-2019-dc-v20210112

Query metadata directory listings

Use the following commands to query metadata directory listings. Directory listings are metadata entries that contain other metadata keys. Any metadata entry ending in a trailing slash is a directory listing

Linux

  1. Connect to your Linux VM.

  2. To query for a VM instance or project metadata directory, from your Linux VM, run the following command:

      curl "http://metadata.google.internal/computeMetadata/v1/PATH_TO_METADATA_DIRECTORY/" -H "Metadata-Flavor: Google"

    Replace the PATH_TO_METADATA_DIRECTORY with the path to the VM instance or project metadata directory for which you want to recursively query the listings. For example:

    • To view the attributes project metadata directory entry, the path to specify is project/attributes/.
    • To view the disks VM instance metadata directory entry, the path to specify is instance/disks/.

    For example, consider the disks/ entry, which is a directory of disks that is attached to the VM. To query the disks/ entry, complete the following steps:

    1. Run the curl tool command on the disks directory.

      user@myinst:~$ curl "http://metadata.google.internal/computeMetadata/v1/instance/disks/" -H "Metadata-Flavor: Google"

      The output is similar to the following:

      0/
1/
2/

    2. If you want more information about disk 0/ directory, you can then query the specific URL for that directory:

      user@myinst:~$ curl "http://metadata.google.internal/computeMetadata/v1/instance/disks/0/" -H "Metadata-Flavor: Google"

      The output is similar to the following:

      device-name
index
mode
type

    3. Then to query the disk type (type) for disks 0/, you can run the following:

      user@myinst:~$ curl "http://metadata.google.internal/computeMetadata/v1/instance/disks/0/type" -H "Metadata-Flavor: Google"

      The output is similar to the following:

      PERSISTENT

Windows

The disks/ entry is a directory of disks that is attached to the VM. To query the disks entry, complete the following steps:

  1. Connect to your Windows VM.

  2. To query for a VM instance or project metadata directory, from your Windows VM, run the following command:

    $value = (Invoke-RestMethod `
          -Headers @{'Metadata-Flavor' = 'Google'} `
          -Uri "http://metadata.google.internal/computeMetadata/v1/PATH_TO_METADATA_DIRECTORY/")
$value

    Replace the PATH_TO_METADATA_DIRECTORY with the path to the VM instance or project metadata directory for which you want to recursively query the listings. For example:

    • To view the attributes project metadata directory entry, the path to specify is project/attributes/.
    • To view the disks VM instance metadata directory entry, the path to specify is instance/disks/.

    For example, consider the disks/ entry, which is a directory of disks that is attached to the VM. To query the disks/ entry, complete the following steps:

    1. Use the Invoke-RestMethod command on the disks directory.

      PS C:\> 
$value = (Invoke-RestMethod `
          -Headers @{'Metadata-Flavor' = 'Google'} `
          -Uri "http://metadata.google.internal/computeMetadata/v1/instance/disks/")
$value

      The output is similar to the following:

      0/
1/
2/

    2. If you want more information about disk 0/ directory, you can query the specific URL for that directory:

      PS C:\> 
$value = (Invoke-RestMethod `
          -Headers @{'Metadata-Flavor' = 'Google'} `
          -Uri "http://metadata.google.internal/computeMetadata/v1/instance/disks/0/")
$value

      The output is similar to the following:

      device-name
index
mode
type

    3. Then to query the disk type (type) for disks 0/, you can run the following:

      PS C:\> 
$value = (Invoke-RestMethod `
          -Headers @{'Metadata-Flavor' = 'Google'} `
          -Uri "http://metadata.google.internal/computeMetadata/v1/instance/disks/0/type")
$value

      The output is similar to the following:

      PERSISTENT

Recursively query directory listings

If you want to return all contents under a directory, use the recursive=true query parameter with your request:

Linux

  1. Connect to your Linux VM.

  2. From your Linux VM, use the curl tool to make a query. To recursively query the listings for a VM instance or project metadata directory, run the following command:

    curl "http://metadata.google.internal/computeMetadata/v1/PATH_TO_METADATA_DIRECTORY/?recursive=true" -H "Metadata-Flavor: Google"

    Replace the PATH_TO_METADATA_DIRECTORY with the path to the VM instance or project metadata directory for which you want to recursively query the listings. For example:

    • To view the attributes project metadata directory entry, the path to specify is project/attributes/.
    • To view the disks VM instance metadata directory entry, the path to specify is instance/disks/.

    For example, the following command recursively queries the instance metadata listings for the disks/ directory.

      user@myinst:~$ curl "http://metadata.google.internal/computeMetadata/v1/instance/disks/?recursive=true" -H "Metadata-Flavor: Google"

    The output is similar to the following:

      [{"deviceName":"boot","index":0,"mode":"READ_WRITE","type":"PERSISTENT"},
  {"deviceName":"persistent-disk-1","index":1,"mode":"READ_WRITE","type":"PERSISTENT"},
  {"deviceName":"persistent-disk-2","index":2,"mode":"READ_ONLY","type":"PERSISTENT"}]

    By default, recursive contents are returned in JSON format. If you want to return these contents in text format, append the alt=text query parameter:

      user@myinst:~$ curl "http://metadata.google.internal/computeMetadata/v1/instance/disks/?recursive=true&alt=text" -H "Metadata-Flavor: Google"

    The output is similar to the following:

      0/device-name boot
  0/index 0
  0/mode READ_WRITE
  0/type PERSISTENT
  1/device-name persistent-disk-1
  1/index 1
  1/mode READ_WRITE
  1/type PERSISTENT
  2/device-name persistent-disk-1
  2/index 2
  2/mode READ_ONLY
  2/type PERSISTENT

Windows

  1. Connect to your Windows VM.

  2. From your Windows VM, use the Invoke-RestMethod command to make a query. To recursively query the listings for a VM instance or project metadata directory, run the following command:

      $value = (Invoke-RestMethod -Headers @{'Metadata-Flavor' = 'Google'}
            -Uri "http://metadata.google.internal/computeMetadata/v1/PATH_TO_METADATA_DIRECTORY/?recursive=true")
  $value

    Replace the PATH_TO_METADATA_DIRECTORY with the path to the VM instance or project metadata directory for which you want to recursively query the listings. For example:

    • To view the attributes project metadata directory entry, the path to specify is project/attributes/.
    • To view the disks VM instance metadata directory entry, the path to specify is instance/disks/.

    For example, the following command recursively queries the instance metadata listings for the disks/ directory.

    PS C:\> 
$value = (Invoke-RestMethod `
          -Headers @{'Metadata-Flavor' = 'Google'} `
          -Uri "http://metadata.google.internal/computeMetadata/v1/instance/disks/?recursive=true")
$value

    The output is similar to the following:

    [{"deviceName":"boot","index":0,"mode":"READ_WRITE","type":"PERSISTENT"},
{"deviceName":"persistent-disk-1","index":1,"mode":"READ_WRITE","type":"PERSISTENT"},
{"deviceName":"persistent-disk-2","index":2,"mode":"READ_ONLY","type":"PERSISTENT"}]

    By default, recursive contents are returned in JSON format. If you want to return these contents in text format, append the alt=text query parameter:

    PS C:\> 
$value = (Invoke-RestMethod `
          -Headers @{'Metadata-Flavor' = 'Google'} `
          -Uri "http://metadata.google.internal/computeMetadata/v1/instance/disks/?recursive=true&alt=text")
$value

    The output is similar to the following:

    0/device-name boot
0/index 0
0/mode READ_WRITE
0/type PERSISTENT
1/device-name persistent-disk-1
1/index 1
1/mode READ_WRITE
1/type PERSISTENT
2/device-name persistent-disk-1
2/index 2
2/mode READ_ONLY
2/type PERSISTENT

Format query output

By default, each endpoint has a predefined format for the response. Some endpoints might return data in JSON format by default, while other endpoints might return data as a string. You can override the default data format specification by using the alt=json or alt=text query parameters, which return data in JSON string format or as a plain text representation, respectively.

Linux

  1. Connect to your Linux VM.

  2. From your Linux VM, use the curl tool to make a query. To change the query response data format for a VM instance or project metadata entry, run the following command:

    curl "http://metadata.google.internal/computeMetadata/v1/PATH_TO_METADATA_ENTRY?alt=DATA_FORMAT" -H "Metadata-Flavor: Google"

    Replace the following:

    • Replace the PATH_TO_METADATA_ENTRY with the path to the VM instance or project metadata key for which you want to query the value. If the key is in a sub-directory of the instance or project directory, ensure to also include the sub-directory. For example:

      • To view the project-id metadata key, which is stored in project metadata, specify project/project-id.
      • To view the image metadata key, which is stored in VM instance metadata, specify instance/image.
      • To view the enable-oslogin which can be stored in the attributes sub-directory of either project or VM instance metadata, specify either project/attributes/enable-oslogin or instance/attributes/enable-oslogin depending on your use case.
    • DATA_FORMAT: the format in which you want the query response data—for example, text or json.

Example

For example, the tags key automatically returns data in JSON format. You can return data in text format instead, by specifying the alt=text query parameter.

Default query

  user@myinst:~$ curl "http://metadata.google.internal/computeMetadata/v1/instance/tags" -H "Metadata-Flavor: Google"

The output is similar to the following:

  ["http-server", "db-client", "app-server", "mysql-server"]

Query with formatting

  user@myinst:~$ curl "http://metadata.google.internal/computeMetadata/v1/instance/tags?alt=text" -H "Metadata-Flavor: Google"

The output is similar to the following:

  http-server
  db-client
  app-server
  mysql-server

Windows

  1. Connect to your Windows VM.

  2. From your Windows VM, use the Invoke-RestMethod command to make a query. To change the query response data format for a VM instance or project metadata entry, run the following command:

      $value = (Invoke-RestMethod -Headers @{'Metadata-Flavor' = 'Google'}
            -Uri "http://metadata.google.internal/computeMetadata/v1/PATH_TO_METADATA_ENTRY?alt=DATA_FORMAT")
  $value

    Replace the following:

    • Replace the PATH_TO_METADATA_ENTRY with the path to the VM instance or project metadata key for which you want to query the value. If the key is in a sub-directory of the instance or project directory, ensure to also include the sub-directory. For example:

      • To view the project-id metadata key, which is stored in project metadata, specify project/project-id.
      • To view the image metadata key, which is stored in VM instance metadata, specify instance/image.
      • To view the enable-oslogin which can be stored in the attributes sub-directory of either project or VM instance metadata, specify either project/attributes/enable-oslogin or instance/attributes/enable-oslogin depending on your use case.
    • DATA_FORMAT: the format in which you want the query response data—for example, text or json.

Example

For example, the tags key automatically returns data in JSON format. You can return data in text format instead, by specifying the alt=text query parameter.

Default query

  PS C:> 
  $value = (Invoke-RestMethod -Headers @{'Metadata-Flavor' = 'Google'}
            -Uri "http://metadata.google.internal/computeMetadata/v1/instance/tags")
  $value

The output is similar to the following:

  ["http-server", "db-client", "app-server", "mysql-server"]

Query with formatting

  PS C:> 
  $value = (Invoke-RestMethod -Headers @{'Metadata-Flavor' = 'Google'}
            -Uri "http://metadata.google.internal/computeMetadata/v1/instance/tags?alt=text")
  $value

The output is similar to the following:

  http-server
  db-client
  app-server
  mysql-server

Query metadata changes using the wait-for-change feature

Given that metadata values can change while your VM is running, the metadata server can be notified of metadata changes by using the wait-for-change feature. With this option, the request only returns an output when your specified metadata has changed.

You can use this feature on custom metadata or server-defined metadata, so if anything changes about your VM or project, or if someone updates a custom metadata entry, you can programmatically react to the change.

For example, you can perform a request on the tags key so that the request only returns if the contents of the tags metadata has changed. When the request returns, it provides the new value of that metadata key.

The wait-for-change feature also lets you match with your request and set timeouts.

When working with thewait-for-change feature, consider the following:

  • You can only perform a wait-for-change request on a metadata endpoint or recursively on the contents of a directory. You cannot perform a wait-for-change request on a directory listing. If you try to do this, the metadata server fails your request and returns a 400 Invalid Request error.

  • You cannot perform a wait-for-change request for a service account token. If you try to make a wait-for-change request to the service account token URL, the request fails immediately and returns a 400 Invalid Request error.

To perform a wait-for-change request, query a metadata key and append the ?wait_for_change=true query parameter:

Linux

  1. Connect to your Linux VM.

  2. From your Linux VM, use the curl tool to make a query. To perform a wait-for-change request for a VM instance or project metadata entry, run the following command:

    curl "http://metadata.google.internal/computeMetadata/v1/PATH_TO_METADATA_ENTRY?wait_for_change=true" -H "Metadata-Flavor: Google"

    Replace the PATH_TO_METADATA_ENTRY with the path to the VM instance or project metadata key for which you want to query the value. If the key is in a sub-directory of the instance or project directory, ensure to also include the sub-directory. For example:

    • To view the project-id metadata key, which is stored in project metadata, specify project/project-id.
    • To view the image metadata key, which is stored in VM instance metadata, specify instance/image.
    • To view the enable-oslogin which can be stored in the attributes sub-directory of either project or VM instance metadata, specify either project/attributes/enable-oslogin or instance/attributes/enable-oslogin depending on your use case.

    After there is a change to the specified metadata key, the query returns with the new value.

Examples

In this example, if a request is made to the setInstanceTags method, the request returns with the new values:

  user@myinst:~$ curl "http://metadata.google.internal/computeMetadata/v1/instance/tags?wait_for_change=true" -H "Metadata-Flavor: Google"

The output is similar to the following:

  http-server
  db-client

You can also perform a wait-for-change request recursively on the contents of a directory:

  user@myinst:~$ curl "http://metadata.google.internal/computeMetadata/v1/instance/attributes/?recursive=true&wait_for_change=true" -H "Metadata-Flavor: Google"

The metadata server returns the new contents if there is any change:

  {"foo":"bar","baz":"bat"}

Windows

  1. Connect to your Windows VM.

  2. From your Windows VM, use the Invoke-RestMethod command to make a query. To perform a wait-for-change request for a VM instance or project metadata entry, run the following command:

    $value = (Invoke-RestMethod `
          -Headers @{'Metadata-Flavor' = 'Google'} `
          -Uri "http://metadata.google.internal/computeMetadata/v1/PATH_TO_METADATA_ENTRY?wait_for_change=true")
$value

    Replace the PATH_TO_METADATA_ENTRY with the path to the VM instance or project metadata key for which you want to query the value. If the key is in a sub-directory of the instance or project directory, ensure to also include the sub-directory. For example:

    • To view the project-id metadata key, which is stored in project metadata, specify project/project-id.
    • To view the image metadata key, which is stored in VM instance metadata, specify instance/image.
    • To view the enable-oslogin which can be stored in the attributes sub-directory of either project or VM instance metadata, specify either project/attributes/enable-oslogin or instance/attributes/enable-oslogin depending on your use case.

    After there is a change to the specified metadata key, the query returns with the new value.

Examples

After there is a change to the specified metadata key, the query returns with the new value. In this example, if a request is made to the setInstanceTags method, the request returns with the new values:

  PS C:> 
  $value = (Invoke-RestMethod -Headers @{'Metadata-Flavor' = 'Google'}
            -Uri "http://metadata.google.internal/computeMetadata/v1/instance/tags?wait_for_change=true")
  $value

The output is similar to the following:

  http-server
  db-client

You can also perform a wait-for-change request recursively on the contents of a directory:

  PS C:> 
  $value = (Invoke-RestMethod -Headers @{'Metadata-Flavor' = 'Google'}
            -Uri "http://metadata.google.internal/computeMetadata/v1/instance/attributes?recursive=true&wait_for_change=true")
  $value

The metadata server returns the new contents if there is any change:

  {"foo":"bar","baz":"bat"}

Use ETags

When you submit a wait-for-change query, the metadata server returns a response if anything has changed in the contents of that metadata. However, there is an inherent race condition between a metadata update and a wait-for-change request being issued, so it's useful to have a reliable way to know you are getting the latest metadata value.

To help with this, you can use the last_etag query parameter, which compares the ETag value you provide with the ETag value saved on the metadata server. If the ETag values match, then the wait-for-change request is accepted. If the ETag values don't match, this indicates that the contents of the metadata has changed since the last time you retrieved the ETag value, and the metadata server returns immediately with this latest value.

Linux VMs

To get the current ETag value for a metadata key, complete the following steps:

  1. Connect to your Linux VM.

  2. Make a request to that key and print the headers. To do this, use the curl tool with the -v flag. To get the current ETag for a VM instance or project metadata entry, run the following command:

    curl -v "http://metadata.google.internal/computeMetadata/v1/PATH_TO_METADATA_ENTRY" -H "Metadata-Flavor: Google"

    Replace the PATH_TO_METADATA_ENTRY with the path to the VM instance or project metadata key for which you want to query the value. If the key is in a sub-directory of the instance or project directory, ensure to also include the sub-directory. For example:

    • To view the project-id metadata key, which is stored in project metadata, specify project/project-id.
    • To view the image metadata key, which is stored in VM instance metadata, specify instance/image.
    • To view the enable-oslogin which can be stored in the attributes sub-directory of either project or VM instance metadata, specify either project/attributes/enable-oslogin or instance/attributes/enable-oslogin depending on your use case.

    For example, the following command gets the current ETag value for the tags instance metadata key.

      user@myinst:~$ curl -v "http://metadata.google.internal/computeMetadata/v1/instance/tags" -H "Metadata-Flavor: Google"

    The output is similar to the following:

    * About to connect() to metadata port 80 (#0)
* Trying 169.254.169.254... connected
* Connected to metadata (169.254.169.254) port 80 (#0)
> GET /computeMetadata/v1/instance/tags HTTP/1.1
> User-Agent: curl/7.19.7 (x86_64-pc-linux-gnu) libcurl/7.19.7 OpenSSL/0.9.8k zlib/1.2.3.3 libidn/1.15
> Host: metadata
> Accept: */*
>
< HTTP/1.1 200 OK
< Content-Type: application/text
< ETag: 411261ca6c9e654e
< Date: Wed, 13 Feb 2013 22:43:45 GMT
< Server: Metadata Server for VM
< Content-Length: 26
< X-XSS-Protection: 1; mode=block
< X-Frame-Options: SAMEORIGIN
<
http-server
db-client

  3. You can then use that ETag value with the curl tool command in your wait-for-change request. To use the ETag value for the wait-for-change request of instance or project metadata, run the following command:

      curl "http://metadata.google.internal/computeMetadata/v1/PATH_TO_METADATA_ENTRY?wait_for_change=true&last_etag=ETAG" -H "Metadata-Flavor: Google"

    Replace the following:

    • Replace the PATH_TO_METADATA_ENTRY with the path to the VM instance or project metadata key for which you want to query the value. If the key is in a sub-directory of the instance or project directory, ensure to also include the sub-directory. For example:

      • To view the project-id metadata key, which is stored in project metadata, specify project/project-id.
      • To view the image metadata key, which is stored in VM instance metadata, specify instance/image.
      • To view the enable-oslogin which can be stored in the attributes sub-directory of either project or VM instance metadata, specify either project/attributes/enable-oslogin or instance/attributes/enable-oslogin depending on your use case.
    • ETAG: the ETag value for the metadata key.

    In this example, the following command uses the ETag value for the tags key and queries for the instance metadata entry.

      user@myinst:~$ curl "http://metadata.google.internal/computeMetadata/v1/instance/tags?wait_for_change=true&last_etag=411261ca6c9e654e" -H "Metadata-Flavor: Google"

    The metadata server matches your specified ETag value, and if that value changes, the request returns with the new contents of your metadata key.

Windows VMs

To get the current ETag value for a metadata key, complete the following steps:

  1. Connect to your Windows VM.

  2. Make a request to that key and print the headers. On Windows, use the Invoke-WebRequest command. To get the current ETag for a VM instance or project metadata entry, run the following command:

      $value = (Invoke-WebRequest -Headers @{'Metadata-Flavor' = 'Google'} `
  -Uri http://metadata.google.internal/computeMetadata/v1/PATH_TO_METADATA_ENTRY)
    


    $value.Headers.ETag

    Replace the PATH_TO_METADATA_ENTRY with the path to the VM instance or project metadata key for which you want to query the value. If the key is in a sub-directory of the instance or project directory, ensure to also include the sub-directory. For example:

    • To view the project-id metadata key, which is stored in project metadata, specify project/project-id.
    • To view the image metadata key, which is stored in VM instance metadata, specify instance/image.
    • To view the enable-oslogin which can be stored in the attributes sub-directory of either project or VM instance metadata, specify either project/attributes/enable-oslogin or instance/attributes/enable-oslogin depending on your use case.

    For example, the following command gets the current ETag value for the tags instance metadata key.

      PS C:> 
  $value = (Invoke-WebRequest -Headers @{'Metadata-Flavor' = 'Google'} `
  -Uri http://metadata.google.internal/computeMetadata/v1/instance/tags)
    


    $value.Headers.ETag

    The output is similar to the following:

      * About to connect() to metadata port 80 (#0)
  * Trying 169.254.169.254... connected
  * Connected to metadata (169.254.169.254) port 80 (#0)
  > GET /computeMetadata/v1/instance/tags HTTP/1.1
  > User-Agent: curl/7.19.7 (x86_64-pc-linux-gnu) libcurl/7.19.7 OpenSSL/0.9.8k zlib/1.2.3.3 libidn/1.15
  > Host: metadata
  > Accept: /
  >
  < HTTP/1.1 200 OK
  < Content-Type: application/text
  < ETag: 411261ca6c9e654e
  < Date: Wed, 13 Feb 2013 22:43:45 GMT
  < Server: Metadata Server for VM
  < Content-Length: 26
  < X-XSS-Protection: 1; mode=block
  < X-Frame-Options: SAMEORIGIN
  <
  http-server
  db-client

  3. You can then use that ETag value in your wait-for-change request. To use the ETag value for the wait-for-change request of instance or project metadata, run the following command:

      $value = (Invoke-RestMethod -Headers @{'Metadata-Flavor' = 'Google'}
          -Uri "http://metadata.google.internal/computeMetadata/v1/PATH_TO_METADATA_ENTRY?wait_for_change=true&last_etag=ETAG")
  $value

    Replace the following:

    • Replace the PATH_TO_METADATA_ENTRY with the path to the VM instance or project metadata key for which you want to query the value. If the key is in a sub-directory of the instance or project directory, ensure to also include the sub-directory. For example:

      • To view the project-id metadata key, which is stored in project metadata, specify project/project-id.
      • To view the image metadata key, which is stored in VM instance metadata, specify instance/image.
      • To view the enable-oslogin which can be stored in the attributes sub-directory of either project or VM instance metadata, specify either project/attributes/enable-oslogin or instance/attributes/enable-oslogin depending on your use case.
    • ETAG: the ETag value for the metadata key.

    In this example, the following command uses the ETag value for the tags key and queries for the instance metadata entry.

      PS C:> 
  $value = (Invoke-RestMethod -Headers @{'Metadata-Flavor' = 'Google'}
            -Uri "http://metadata.google.internal/computeMetadata/v1/instance/tags?wait_for_change=true&last_etag=411261ca6c9e654e")
  $value

    The metadata server matches your specified ETag value, and if that value changes, the request returns with the new contents of your metadata key.

Python

The following Python sample shows how to programmatically watch the metadata server for changes.

This sample sets the initial ETag to 0. The metadata server will not return a response with 0 as the ETag value. When 0 is specified as the last ETag in a request, the metadata server responds with the current value and ETag. This saves a bit of the code needed to get the initial value and ETag.

last_etag = "0"

while True:
    r = requests.get(
        url,
        params={"last_etag": last_etag, "wait_for_change": True},
        headers=METADATA_HEADERS,
    )

    # During maintenance the service can return a 503, so these should
    # be retried.
    if r.status_code == 503:
        time.sleep(1)
        continue
    r.raise_for_status()

    last_etag = r.headers["etag"]

Set timeouts

If you would like your wait-for-change request to time out after a certain number of seconds, you can set the timeout_sec parameter. The timeout_sec parameter limits the wait time of your request to the number of seconds you specified, and when the request reaches that limit, it returns the current contents of the metadata key.

When you set the timeout_sec parameter, the request always returns after the specified number of seconds, whether or not the metadata value has actually changed. It is only possible to set an integer value for your timeout.

Linux

  1. Connect to your Linux VM.

  2. From your Linux VM, use the curl tool to make a query. To perform a wait-for-change request with a time out value for a VM instance or project metadata entry, run the following command:

      curl "http://metadata.google.internal/computeMetadata/v1/PATH_TO_METADATA_ENTRY?wait_for_change=true&timeout_sec=TIMEOUT" -H "Metadata-Flavor: Google"

    Replace the following:

    • Replace the PATH_TO_METADATA_ENTRY with the path to the VM instance or project metadata key for which you want to query the value. If the key is in a sub-directory of the instance or project directory, ensure to also include the sub-directory. For example:

      • To view the project-id metadata key, which is stored in project metadata, specify project/project-id.
      • To view the image metadata key, which is stored in VM instance metadata, specify instance/image.
      • To view the enable-oslogin which can be stored in the attributes sub-directory of either project or VM instance metadata, specify either project/attributes/enable-oslogin or instance/attributes/enable-oslogin depending on your use case.
    • TIMEOUT: the time out value.

For example, the following command performs a wait-for-change request that is set to time out after 360 seconds:

  user@myinst:~$ curl "http://metadata.google.internal/computeMetadata/v1/instance/tags?wait_for_change=true&timeout_sec=360" -H "Metadata-Flavor: Google"

Windows

  1. Connect to your Windows VM.

  2. From your Windows VM, use the Invoke-RestMethod command to make a query. To perform a wait-for-change request with a time out value for a VM instance or project metadata entry, run the following command:

      $value = (Invoke-RestMethod -Headers @{'Metadata-Flavor' = 'Google'}
          -Uri "http://metadata.google.internal/computeMetadata/v1/PATH_TO_METADATA_ENTRY?wait_for_change=true&timeout_sec=TIMEOUT")
  $value

    Replace the following:

    • Replace the PATH_TO_METADATA_ENTRY with the path to the VM instance or project metadata key for which you want to query the value. If the key is in a sub-directory of the instance or project directory, ensure to also include the sub-directory. For example:

      • To view the project-id metadata key, which is stored in project metadata, specify project/project-id.
      • To view the image metadata key, which is stored in VM instance metadata, specify instance/image.
      • To view the enable-oslogin which can be stored in the attributes sub-directory of either project or VM instance metadata, specify either project/attributes/enable-oslogin or instance/attributes/enable-oslogin depending on your use case.
    • TIMEOUT: the time out value.

For example, the following command performs a wait-for-change request that is set to time out after 360 seconds:

  PS C:> 
  $value = (Invoke-RestMethod -Headers @{'Metadata-Flavor' = 'Google'}
            -Uri "http://metadata.google.internal/computeMetadata/v1/instance/tags?wait_for_change=true&timeout_sec=360")
  $value

Query metadata by using the HTTPS metadata server endpoint

The HTTPS metadata server endpoint (https://metadata.google.internal/computeMetadata/v1) provides added security for transmission of information between the metadata server and the VM.

To use the HTTPS metadata server endpoint, review the following requirements:

  • You must request access to the HTTPS metadata server endpoint preview.

  • After your project is added to the allowlist, you can create the VM. The VM must meet the following requirements:

    • The guest environment must be running on the VM.
    • The VM must be a Shielded VM. This is because the HTTPS metadata server requires the use of Unified Extensible Firmware Interface (UEFI) and Virtual Trusted Platform Module (vTPM) for verifying certificates.

For an overview of how queries to the HTTPS metadata server endpoint are handled, see HTTPS metadata server endpoint. You can perform all the same queries to the metadata server whether you use the https or the http endpoint. However, to call the https endpoint you must specify the path to the client identity certificates and in some cases the root certificate.

The following commands demonstrate how to query the metadata server by using the https endpoint.

Linux

  1. Connect to your Linux VM.

  2. From your Linux VM, use the curl tool to make a query and specify the client identity certificate. Optionally, you can also specify the root certificate.

    curl "https://metadata.google.internal/computeMetadata/v1/PATH_TO_METADATA_ENTRY" \
  -E CLIENT_CERTIFICATE \
  [--cacert ROOT_CERTIFICATE] \
  -H "Metadata-Flavor: Google"

    Replace the following:

    • Replace the PATH_TO_METADATA_ENTRY with the path to the VM instance or project metadata key for which you want to query the value. If the key is in a sub-directory of the instance or project directory, ensure to also include the sub-directory. For example:

      • To view the project-id metadata key, which is stored in project metadata, specify project/project-id.
      • To view the image metadata key, which is stored in VM instance metadata, specify instance/image.
      • To view the enable-oslogin which can be stored in the attributes sub-directory of either project or VM instance metadata, specify either project/attributes/enable-oslogin or instance/attributes/enable-oslogin depending on your use case.
    • CLIENT_CERTIFICATE: the path to the client identity certificate: /run/google-mds-mtls/client.key.
    • Optional: ROOT_CERTIFICATE: the path to the root certificate: /run/google-mds-mtls/root.crt.

    For example, to query the boot image for a VM, run the following query:

    user@myinst:~$ 
curl "https://metadata.google.internal/computeMetadata/v1/instance/image" \
  -E /run/google-mds-mtls/client.key \
  -H "Metadata-Flavor: Google"

    The output is similar to the following:

    projects/rhel-cloud/global/images/rhel-8-v20210122

    If you see an error message, review the troubleshooting documentation.

Windows

  1. Connect to your Windows VM.

  2. Get the client identity certificate by using one of the following commands:

    • $cert = Get-PfxCertificate -FilePath "C:\ProgramData\Google\Compute Engine\mds-mtls-client.key.pfx"

    • $cert = Get-ChildItem Cert:\LocalMachine\My | Where-Object { $_.Issuer -like "google.internal" }

  3. From your Windows VM, use the Invoke-RestMethod command and specify the client identity certificate to make a query.

    PS C:\> 
$value = (Invoke-RestMethod `
          -Headers @{'Metadata-Flavor' = 'Google'} -Certificate CLIENT_CERTIFICATE `
          -Uri "https://metadata.google.internal/computeMetadata/v1/PATH_TO_METADATA_ENTRY")
$value

    Replace the following:

    • CLIENT_CERTIFICATE: the path to the client identity certificate on the VM. This is the $cert variable that is set in the previous step.

    • Replace the PATH_TO_METADATA_ENTRY with the path to the VM instance or project metadata key for which you want to query the value. If the key is in a sub-directory of the instance or project directory, ensure to also include the sub-directory. For example:

      • To view the project-id metadata key, which is stored in project metadata, specify project/project-id.
      • To view the image metadata key, which is stored in VM instance metadata, specify instance/image.
      • To view the enable-oslogin which can be stored in the attributes sub-directory of either project or VM instance metadata, specify either project/attributes/enable-oslogin or instance/attributes/enable-oslogin depending on your use case.

    For example, to query the boot image for a Windows server 2019 VM, run the following query:

    PS C:\> 
$value = (Invoke-RestMethod `
          -Headers @{'Metadata-Flavor' = 'Google'} -Certificate $cert `
          -Uri "https://metadata.google.internal/computeMetadata/v1/instance/image")
$value

    The output is similar to the following:

    projects/windows-cloud/global/images/windows-server-2019-dc-v20210112

Limitations

  • Any requests that contain the header X-Forwarded-For are automatically rejected by the metadata server. This header generally indicates that the request was proxied and might not be a request made by an authorized user. For security reasons, all such requests are rejected.

  • When you use the curl command to retrieve metadata from the server, note that some encoded characters aren't supported in the request path. Encoded characters are only supported in the query path.

    For example, the following request might not work:

    curl "http://metadata.google.internal/computeMetadata/v1/instance/service-accounts/123456789-compute%40developer.gserviceaccount.com/?query_path=https%3A%2F%2Flocalhost%3A8200%2Fexample%2Fquery&another_param=true" -H "Metadata-Flavor: Google"

    For this request to work, you must replace the unsupported encoded character in the request path (%40) with the equivalent accepted value (@).

    curl "http://metadata.google.internal/computeMetadata/v1/instance/service-accounts/1234567898-compute@developer.gserviceaccount.com/?query_path=https%3A%2F%2Flocalhost%3A8200%2Fexample%2Fquery&another_param=true" -H "Metadata-Flavor: Google"

    The following table summarises the encoded characters that aren't supported in a request path.

    Encoded character Accepted value
    %21 
    !
    %24 
    $
    %27 
    '
    %28 
    (
    %29 
    )
    %2A 
    *
    %2C 
    ,
    %40 
    @

Status codes

When you make a request to the metadata server, the metadata server returns standard HTTP status codes to indicate success or failure. Sometimes, network conditions or host events can cause the metadata server to fail your request and return an error code. In these cases, you should design your application to be fault-tolerant and to be able to recognize and handle these errors.

For a detailed list of status codes that can be returned, see Troubleshoot server codes.

View the custom metadata for your VMs

You can view the custom metadata values for your Compute Engine VMs in one of the following ways:

View project metadata

To view custom metadata that applies to all VMs in your project, use one of the following methods.

Console

  1. In the Google Cloud console, go to the Metadata page.

    Go to the Metadata page

    On the Metadata page,you see a list of all custom project metadata entries for your project.

gcloud

Use the gcloud compute project-info describe command to query project metadata:

gcloud compute project-info describe --flatten="commonInstanceMetadata[]"

The output is similar to the following:

---
fingerprint: HcSFdS_1_1I=
items:
- key: ssh-keys
  value: USERNAME:ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDWZ...
kind: compute#metadata

REST

To query project metadata, create a GET request to the project.get method.

Replace PROJECT_ID with your project ID.

GET https://compute.googleapis.com/compute/v1/projects/PROJECT_ID

The output is similar to the following:

"kind": "compute#project",
"id": "XXXXXXX",
"creationTimestamp": "2018-12-10T08:34:33.616-08:00",
"name": "YOUR_PROJECT",
"commonInstanceMetadata": {
  "kind": "compute#metadata",
  "fingerprint": "XXXXXCdg=",
  "items": [
    {
      "key": "enable-guest-attributes",
      "value": "TRUE"
    },
    {
      "key": "enable-os-inventory",
      "value": "true"
    },
    {
      "key": "enable-osconfig",
      "value": "TRUE"
    },
    {
      "key": "enable-oslogin",
      "value": "TRUE"
    },
    {
      "key": "sshKeys",
      "value": "XXXXX"
    }
  ]
}, ...

View zonal metadata

To view custom metadata that applies to all VM instances in a specific zone in a project, use one of the following methods.

gcloud

To query the custom zonal metadata, use the gcloud compute project-zonal-metadata describe command.

gcloud compute project-zonal-metadata describe \
    --zone=ZONE \
    --project=PROJECT_ID

Replace the following:

  • PROJECT_ID: your project ID
  • ZONE: the zone for which you want to view the zonal metadata.

The output is similar to the following:

{
  "fingerprint": "VlRIl8dx9vk=",
  "metadata": {
    items: {
      "key-1": "value-1",
      "key-2": "value-2"
    }
  }
}

REST

To query the custom zonal metadata, make a GET request to the instanceSettings().get method

GET https://compute.googleapis.com/compute/v1/projects/PROJECT_ID/zones/ZONE/instanceSettings

Replace the following:

  • PROJECT_ID: your project ID
  • ZONE: the zone for which you want to view the zonal metadata.

The output is similar to the following:

{
  "fingerprint": "VlRIl8dx9vk=",
  "metadata": {
    items: {
      "key-1": "value-1",
      "key-2": "value-2"
    }
  }
}

View instance metadata

To view metadata that applies to a single VM in your project, use one of the following methods.

Console

  1. In the Google Cloud console, go to the VM instances page.

    Go to VM instances

  2. Click the name of the VM for which you want to view metadata.

    • SSH keys for this VM. In the Security and access section, view the SSH keys field.

      • A value of None indicates there are no SSH keys stored in instance metadata.

      • Any other value indicates that there are SSH keys stored in instance metadata.

    • SSH keys for a project. In the Security and access section, view the Block project-wide SSH keys field.

      • A value of On indicates that the value of the metadata key block-project-ssh-keys is TRUE in instance metadata.

      • A value of Off indicates that the value of the metadata key block-project-ssh-keys is FALSE, or that the key isn't set.

    • All other custom metadata. View the Custom metadata section. You see all custom metadata keys and values, other than SSH key metadata.

gcloud

Use the gcloud compute instances describe command to query instance metadata:

gcloud compute instances describe VM_NAME --flatten="metadata[]"

Replace VM_NAME with the name of the VM you want to find metadata for.

The output is similar to the following:

---
fingerprint: MTgTJ5m-Cjs=
items:
- key: enable-oslogin
  value: 'true'
kind: compute#metadata

REST

To query metadata for a specific VM, send a GET request to the instances.get method.

GET https://compute.googleapis.com/compute/v1/projects/PROJECT_ID/zones/ZONE/instances/VM_NAME

The output is similar to the following:

......
"metadata": {
"kind": "compute#metadata",
"fingerprint": "XXXXXXVo=",
"items": [
  {
    "key": "enable-oslogin",
    "value": "true"
  }
]
},....

Replace the following:

  • PROJECT_ID: your project ID
  • ZONE: the zone where the VM is located
  • VM_NAME: the name of the VM

What's next