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By default, the Container-Optimized OS host firewall allows outgoing
connections and accepts incoming connections only through the SSH service. You
can see the exact host firewall configuration by running sudo iptables -L on a
VM instance running Container-Optimized OS.
Keep in mind that the host firewall is different from Virtual Private Cloud firewall
rules, which must also be configured for your applications to work correctly.
See the Firewall Rules Overview to learn more about
Virtual Private Cloud firewall rules.
Running containers in Docker's default network namespace
If you are deploying a container on Container-Optimized OS that must be
accessible over the network and you are not using Docker's --net=host option,
run your container with Docker's -p option. With this option, Docker will
automatically configure the host firewall to expose your application on the
network. See the
Docker run reference to learn
more about Docker run options.
In the following example, the nginx container will be accessible on the
network on port 80:
dockerrun--rm-d-p80:80--name=nginxnginx
Running containers in the host's network namespace
If you are deploying a container on Container-Optimized OS that must be
accessible over the network and you are using Docker's --net=host option, you
must explicitly configure the host firewall yourself.
You can configure the host firewall with standard iptables commands. As with
most GNU/Linux distributions, firewall rules configured with iptables commands
will not persist across reboots. To ensure that the host firewall is correctly
configured on every boot, configure the host firewall in your cloud-init
configuration. Consider the following cloud-init example:
#cloud-configwrite_files:-path:/etc/systemd/system/config-firewall.servicepermissions:0644owner:rootcontent:|[Unit]Description=Configures the host firewall[Service]Type=oneshotRemainAfterExit=trueExecStart=/sbin/iptables -A INPUT -p tcp --dport 80 -j ACCEPT-path:/etc/systemd/system/myhttp.servicepermissions:0644owner:rootcontent:|[Unit]Description=My HTTP serviceAfter=docker.service config-firewall.serviceWants=docker.service config-firewall.service[Service]Restart=alwaysExecStart=/usr/bin/docker run --rm --name=%n --net=host nginxExecStop=-/usr/bin/docker exec %n -s quitruncmd:-systemctl daemon-reload-systemctl start myhttp.service
Using this cloud-init configuration with a VM running
Container-Optimized OS will result in the following behaviors on every
boot:
The host firewall will be configured to allow incoming TCP connections on port
80.
An nginx container will listen on port 80 and respond to incoming HTTP
requests.
[[["Easy to understand","easyToUnderstand","thumb-up"],["Solved my problem","solvedMyProblem","thumb-up"],["Other","otherUp","thumb-up"]],[["Hard to understand","hardToUnderstand","thumb-down"],["Incorrect information or sample code","incorrectInformationOrSampleCode","thumb-down"],["Missing the information/samples I need","missingTheInformationSamplesINeed","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-25 UTC."],[[["\u003cp\u003eBy default, Container-Optimized OS allows outgoing connections and only accepts incoming connections via SSH, as seen with the \u003ccode\u003esudo iptables -L\u003c/code\u003e command, but this might vary with other Google Cloud products.\u003c/p\u003e\n"],["\u003cp\u003eUsing Docker's \u003ccode\u003e-p\u003c/code\u003e option automatically configures the host firewall for network accessibility when deploying a container on Container-Optimized OS without \u003ccode\u003e--net=host\u003c/code\u003e.\u003c/p\u003e\n"],["\u003cp\u003eFor IPv6 accessibility, the host firewall must be manually configured using \u003ccode\u003eip6tables\u003c/code\u003e commands because Docker does not automatically configure the IPv6 rules.\u003c/p\u003e\n"],["\u003cp\u003eWhen deploying a container on Container-Optimized OS with Docker's \u003ccode\u003e--net=host\u003c/code\u003e option, you must manually configure the host firewall with \u003ccode\u003eiptables\u003c/code\u003e commands.\u003c/p\u003e\n"],["\u003cp\u003eTo ensure persistent host firewall configurations across reboots when using \u003ccode\u003eiptables\u003c/code\u003e commands, utilize \u003ccode\u003ecloud-init\u003c/code\u003e to set up the firewall rules, such as allowing incoming TCP connections on port 80.\u003c/p\u003e\n"]]],[],null,["# Configuring the host firewall\n\nBy default, the Container-Optimized OS host firewall allows outgoing\nconnections and accepts incoming connections only through the SSH service. You\ncan see the exact host firewall configuration by running `sudo iptables -L` on a\nVM instance running Container-Optimized OS.\n| **Warning:** The default firewall configuration might be different if you are using Container-Optimized OS through another Google Cloud product like [Containers on Compute Engine](/compute/docs/containers/deploying-containers) or Google Kubernetes Engine. Refer to the product specific documentation for more details.\n\nKeep in mind that the host firewall is different from Virtual Private Cloud firewall\nrules, which must also be configured for your applications to work correctly.\nSee the [Firewall Rules Overview](/vpc/docs/firewalls) to learn more about\nVirtual Private Cloud firewall rules.\n\nRunning containers in Docker's default network namespace\n--------------------------------------------------------\n\nIf you are deploying a container on Container-Optimized OS that must be\naccessible over the network and you are not using Docker's `--net=host` option,\nrun your container with Docker's `-p` option. With this option, Docker will\nautomatically configure the host firewall to expose your application on the\nnetwork. See the\n[Docker run reference](https://docs.docker.com/engine/reference/run/) to learn\nmore about Docker run options.\n\nIn the following example, the `nginx` container will be accessible on the\nnetwork on port 80: \n\n docker run --rm -d -p 80:80 --name=nginx nginx\n\n| **Note:** If IPv6 address is used for accessing the deployed container over the network, you must explicitly configure the host firewall using `ip6tables` commands like `\"ip6tables -A INPUT -p tcp --dport 80 -j ACCEPT\"`.This is because Docker does not automatically configure the IPv6 rules for host firewall to expose your application on the network due to [known limitation](https://github.com/moby/moby/issues/21951).\n\nRunning containers in the host's network namespace\n--------------------------------------------------\n\nIf you are deploying a container on Container-Optimized OS that must be\naccessible over the network and you are using Docker's `--net=host` option, you\nmust explicitly configure the host firewall yourself.\n\nYou can configure the host firewall with standard `iptables` commands. As with\nmost GNU/Linux distributions, firewall rules configured with `iptables` commands\nwill not persist across reboots. To ensure that the host firewall is correctly\nconfigured on every boot, configure the host firewall in your `cloud-init`\nconfiguration. Consider the following `cloud-init` example: \n\n #cloud-config\n\n write_files:\n - path: /etc/systemd/system/config-firewall.service\n permissions: 0644\n owner: root\n content: |\n [Unit]\n Description=Configures the host firewall\n\n [Service]\n Type=oneshot\n RemainAfterExit=true\n ExecStart=/sbin/iptables -A INPUT -p tcp --dport 80 -j ACCEPT\n - path: /etc/systemd/system/myhttp.service\n permissions: 0644\n owner: root\n content: |\n [Unit]\n Description=My HTTP service\n After=docker.service config-firewall.service\n Wants=docker.service config-firewall.service\n\n [Service]\n Restart=always\n ExecStart=/usr/bin/docker run --rm --name=%n --net=host nginx\n ExecStop=-/usr/bin/docker exec %n -s quit\n\n runcmd:\n - systemctl daemon-reload\n - systemctl start myhttp.service\n\nUsing this `cloud-init` configuration with a VM running\nContainer-Optimized OS will result in the following behaviors on every\nboot:\n\n- The host firewall will be configured to allow incoming TCP connections on port 80.\n- An `nginx` container will listen on port 80 and respond to incoming HTTP requests.\n\nRefer to\n[Creating and configuring instances](/container-optimized-os/docs/how-to/create-configure-instance)\nto learn more about using `cloud-init` on Container-Optimized OS."]]
