Compare V2 vs V3 Buildpacks

A buildpack converts source code into an executable, and is used to deliver a simple, reliable, and repeatable way to create containers. Kf supports both V2 and V3 buildpacks, and it is important to understand the differences between them.

V2 buildpacks

Most Cloud Foundry applications already use V2 buildpacks. When using V2 buildpacks with Kf, the lifecycle binaries and the buildpacks are downloaded and configured from their git URLs. Kf then uses the lifecycle CLI to execute each buildpack against the source code.

Pros

  • Ready out of the box without pipeline or code changes.

Cons

  • Legacy buildpack supersceded by V3.
  • Weaker performance and reliability. The Kf build pipeline requires more IO for V2 buildpacks.
  • Fewer community resources.
  • Kf only supports OSS git repos.

V3 buildpacks

V3 buildpacks are a Cloud Native Computing Foundation (CNCF) project with a well defined spec, a CLI (pack) and a growing community that is innovating around different languages and frameworks. Google Cloud also has its own set of Google Cloud's buildpacks.

V3 buildpacks have two overarching OCI containers:

  • Builder image
  • Run image

Builder image

The builder image is used while your source code is being built into a runnable container. The image has the necessary detect scripts and other utilities to compile source code.

Run image

The run image is the base image that a container is built on. This means that it is the base image that will run when the App executes.

Layers

V3 buildpacks use layers to compose the final container. Each buildpack included in a build is given the opportunity to manipulate the file system and environment variables of the App. This layering approach allows for buildpacks to be thinner and more generic.

V3 buildpacks are built on OCI containers. This requires that the V3 builder image be stored in a container registry that the Kf build pipeline has access to. The build pipeline uses the builder image to apply the underlying scripts to build the source code into a runnable container.

Pros

Cons

  • May require code/process updates. For example, the Java buildpack requires source code while the V2 buildpack requires a jar file.
  • V3 buildpacks are newer and might require additional validation (is using community developed buildpacks).

Kf Stacks

View Stacks

When pushing an App, the build pipeline determines the buildpack based on the selected Stack (specified via the --stack flag or the manifest).

To see which Stacks are available in a Space first ensure a Space is targeted:

kf target -s myspace

The kf stacks subcommand can then be used to list the Stacks:

kf stacks

The output shows both V2 and V3 Stacks:

Getting stacks in Space: myspace
Version  Name                                Build Image                                                                                          Run Image
V2       cflinuxfs3                          cloudfoundry/cflinuxfs3@sha256:5219e9e30000e43e5da17906581127b38fa6417f297f522e332a801e737928f5      cloudfoundry/cflinuxfs3@sha256:5219e9e30000e43e5da17906581127b38fa6417f297f522e332a801e737928f5
V3       kf-v2-to-v3-shim                    gcr.io/kf-releases/v2-to-v3:v2.7.0                                                                   gcr.io/buildpacks/gcp/run:v1                                                                       This is a stack added by the integration tests to assert that v2->v3 shim works
V3       google                              gcr.io/buildpacks/builder:v1                                                                         gcr.io/buildpacks/gcp/run:v1                                                                       Google buildpacks (https://github.com/GoogleCloudPlatform/buildpacks)
V3       org.cloudfoundry.stacks.cflinuxfs3  cloudfoundry/cnb:cflinuxfs3@sha256:f96b6e3528185368dd6af1d9657527437cefdaa5fa135338462f68f9c9db3022  cloudfoundry/run:full-cnb@sha256:dbe17be507b1cc6ffae1e9edf02806fe0e28ffbbb89a6c7ef41f37b69156c3c2  A large Cloud Foundry stack based on Ubuntu 18.04

Configure Stacks

The Stack configuration can be updated by editing the kfsystem Custom Resource:

kubectl edit kfsystem kfsystem

This example sets the Google Cloud buildpacks a V3 Stack:

spec:
  kf:
    config:
      spaceStacksV3:
      - name: google
        description: Google buildpacks (https://github.com/GoogleCloudPlatform/buildpacks)
        buildImage: gcr.io/buildpacks/builder:v1
        runImage: gcr.io/buildpacks/gcp/run:v1

This new Stack can now be pushed:

kf push myapp --stack google

This example configures the Ruby V2 buildpack and sets the build pipeline defaults to use V2 Stacks:

spec:
  kf:
    config:
      spaceDefaultToV3Stack: false
      spaceBuildpacksV2:
      - name: ruby_buildpack
        url: https://github.com/cloudfoundry/ruby-buildpack
      spaceStacksV2:
      - name: cflinuxfs3
        image: cloudfoundry/cflinuxfs3@sha256:5219e9e30000e43e5da17906581127b38fa6417f297f522e332a801e737928f5

V2 to V3 Buildpack Migration

Kf provides a V3 stack to build applications that were built with standard V2 buildpacks, using a stack named kf-v2-to-v3-shim. The kf-v2-to-v3-shim stack is created following the standard V3 buildpacks API. A Google maintained builder image is created with each Kf release, following the standard buildpack process. The builder image aggregates a list of V3 buildpacks created by the same process used with the kf wrap-v2-buildpack command. The V3 buildpack images are created using the standard V2 buildpack images. It's important to note that the V3 buildpacks do not contain the binary of the referenced V2 buildpacks. Instead, the V2 buildpack images are referenced, and the bits are downloaded at App build time (by running kf push).

At App build time, the V2 buildpack is downloaded from the corresponding git repository. When V3 detection runs, it delegates to the downloaded V2 detection script. For the first buildpack group that passes detection, it proceeds to the build step, which delegates the build execution to the downloaded V2 builder script.

The following V2 buildpacks are supported in the kf-v2-to-v3-shim stack:

Buildpack Git Repository
java_buildpack https://github.com/cloudfoundry/java-buildpack
dotnet_core_buildpack https://github.com/cloudfoundry/dotnet-core-buildpack
nodejs_buildpack https://github.com/cloudfoundry/nodejs-buildpack
go_buildpack https://github.com/cloudfoundry/go-buildpack
python_buildpack https://github.com/cloudfoundry/python-buildpack
binary_buildpack https://github.com/cloudfoundry/binary-buildpack
nginx_buildpack https://github.com/cloudfoundry/nginx-buildpack

Option 1: Migrate Apps built with standard V2 buildpacks

To build Apps with the kf-v2-to-v3-shim stack, use the following command:

kf push myapp --stack kf-v2-to-v3-shim

The kf-v2-to-v3-shim stack will automatically detect the runtime with the wrapped V2 buildpacks. The resulting App image is created using the V3 standard and build pipeline, but the builder of the equivalent V2 buildpack.

Option 2: Migrate Apps built with custom V2 buildpacks

Kf has a buildpack migration tool that can take a V2 buildpack and wrap it with a V3 buildpack. The wrapped buildpack can then be used anywhere V3 buildpacks are available.

kf wrap-v2-buildpack gcr.io/your-project/v2-go-buildpack https://github.com/cloudfoundry/go-buildpack --publish

This will create a buildpack image named gcr.io/your-project/v2-go-buildpack. It can then be used to create a builder by following the create a builder docs.

This subcommand uses the following CLIs transparently:

  • go
  • git
  • pack
  • unzip

It is recommended that you use Cloud Shell Editor to ensure each subcommand is available on the correct path and is the correct version.

Known issues

The following are features that don't yet work with Kf. If one is high priority for your organization, please reach out to your sales representative:

  • Private container registries for V3 builder images.
  • V3 caching.
  • V2 buildpacks that require git credentials.