Restart policy
- Docker & Kubernetes course
- Beginner
- Lesson 33/82
- 4 min
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 restarton-failure[:5]: only on a non-zero exit code, at most 5 timesalways: always; even if stopped by hand it starts when the daemon startsunless-stopped: like always, but doesn't start if it was stopped by hand
docker run -d --name web --restart unless-stopped nginxUpdating 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 2Practice 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.
Starter code
# buraya yazSample solution
docker run -d --name web --restart unless-stopped nginx
docker update --restart on-failure:3 workerExpected output
2c3d4e5f6a7b worker
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Which policy keeps a container you stopped by hand from starting when the server reboots?
- always
- on-failure
- no and always together
- unless-stopped Correct answer
Explanation: always forgets the manual stop when the daemon restarts.
2 Restart only on failure, at most 5 times.
Question
docker run -d --restart ____ worker
Answer
docker run -d --restart on-failure:5 workerExplanation: on-failure:N retries N times on a non-zero exit.
3 Match the policies.
| Term | Meaning |
|---|---|
no |
Never restart |
on-failure |
On an error exit |
always |
Always |
unless-stopped |
Unless stopped by hand |