Restart policy

Learn container restart policy with --restart.

Restart policy

--restart decides what Docker does when the container stops or the server reboots:

no (default): don't restart
on-failure[:5]: only on a non-zero exit code, at most 5 times
always: always; even if stopped by hand it starts when the daemon starts
unless-stopped: like always, but doesn't start if it was stopped by hand

docker run -d --name web --restart unless-stopped nginx

Updating an existing container

The policy can also be changed after the container is created. The current policy and the restart count are seen with docker inspect:

docker update --restart on-failure:3 worker
docker inspect -f '{{.HostConfig.RestartPolicy.Name}} {{.RestartCount}}' worker
# on-failure 2

Exercise Resilient services

Write two commands: run a container named web from nginx in the background so it restarts unless stopped by hand; then update the existing worker container's policy to restart at most 3 times on failure.

Show example solution

docker run -d --name web --restart unless-stopped nginx
docker update --restart on-failure:3 worker

Test yourself

Which policy keeps a container you stopped by hand from starting when the server reboots?
- always
- on-failure
- no and always together
- unless-stopped
Show answer

unless-stopped — always forgets the manual stop when the daemon restarts.

Restart only on failure, at most 5 times.

docker run -d --restart ____ worker

Show answer

docker run -d --restart on-failure:5 worker

Match the policies.

no

Never restart
on-failure

On an error exit
always

Always
unless-stopped

Unless stopped by hand

Next lesson: Working directory

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