Keep containers alive during daemon downtime

By default, when the Docker daemon terminates, it shuts down running containers. Starting with Docker Engine 1.12, you can configure the daemon so that containers remain running if the daemon becomes unavailable. This functionality is called live restore. The live restore option helps reduce container downtime due to daemon crashes, planned outages, or upgrades.

Note

Live restore is not supported on Windows containers, but it does work for Linux containers running on Docker Desktop for Windows.

Enable live restore

There are two ways to enable the live restore setting to keep containers alive when the daemon becomes unavailable. Only do one of the following.

• Add the configuration to the daemon configuration file. On Linux, this defaults to /etc/docker/daemon.json. On Docker Desktop for Mac or Docker Desktop for Windows, select the Docker icon from the task bar, then click Preferences -> Daemon -> Advanced.

  • Use the following JSON to enable live-restore.

    {
      "live-restore": true
    }
    

  • Restart the Docker daemon. On Linux, you can avoid a restart (and avoid any downtime for your containers) by reloading the Docker daemon. If you use systemd, then use the command systemctl reload docker. Otherwise, send a SIGHUP signal to the dockerd process.

• If you prefer, you can start the dockerd process manually with the --live-restore flag. This approach is not recommended because it does not set up the environment that systemd or another process manager would use when starting the Docker process. This can cause unexpected behavior.

Live restore during upgrades

Live restore allows you to keep containers running across Docker daemon updates, but is only supported when installing patch releases (YY.MM.x), not for major (YY.MM) daemon upgrades.

If you skip releases during an upgrade, the daemon may not restore its connection to the containers. If the daemon can’t restore the connection, it cannot manage the running containers and you must stop them manually.

Live restore upon restart

The live restore option only works to restore containers if the daemon options, such as bridge IP addresses and graph driver, did not change. If any of these daemon-level configuration options have changed, the live restore may not work and you may need to manually stop the containers.

Impact of live restore on running containers

If the daemon is down for a long time, running containers may fill up the FIFO log the daemon normally reads. A full log blocks containers from logging more data. The default buffer size is 64K. If the buffers fill, you must restart the Docker daemon to flush them.

On Linux, you can modify the kernel’s buffer size by changing /proc/sys/fs/pipe-max-size. You cannot modify the buffer size on Docker Desktop for Mac or Docker Desktop for Windows.

Live restore and swarm mode

The live restore option only pertains to standalone containers, and not to swarm services. Swarm services are managed by swarm managers. If swarm managers are not available, swarm services continue to run on worker nodes but cannot be managed until enough swarm managers are available to maintain a quorum.