How to automatically restart a Docker container with/from a clean image?

Question

I'm working on introducing build agents in docker container and starting them currently with the following command:

docker run -d --restart=unless-stopped --cpus="4" -m="8g" --name "${AZP_AGENT_NAME}${i}" -e AZP_URL="$AZP_URL" -e AZP_TOKEN="$AZP_TOKEN" -e AZP_AGENT_NAME="${AZP_AGENT_NAME}${i}" -e AZP_POOL="$AZP_POOL" -v /var/run/docker.sock:/var/run/docker.sock -ti dockeragent:latest --once

This allows us to run our build pipeline in docker containers which will restart as soon as the build tasks are complete (container is being shutdown after finishing last task with argument --once.

As --restart=unless-stopped will keep the same container (and underlying file system) when restarting, I have the same state of the container as before (which is probably the intended strategy for most use cases). But as we expect a clean container for each build, this is not the right way.

Is there a way to always restart the container from a fresh image in an initial state?

I tried with the combination of --restart=unless-stopped --rm but this makes docker not happy and replies with docker: Conflicting options: --restart and --rm.. I excepted the container to be removed and be running fresh from the image again. But it probably makes sense this isn't going to work as the intended goal would be to bring up the same container again.

Thanks to @jcragun, I ended up with the following systemd unit configuration:

[Unit]
Description=Dockeragent <Agent-Hostname>-<Agent-Instance>
After=docker.service
Requires=docker.service

[Service]
EnvironmentFile=/etc/systemd/system/<Agent-Hostname>-<Agent-Instance>.service.d/env.conf
TimeoutStartSec=0
Restart=always
ExecStartPre=-/usr/bin/docker stop %n 
ExecStartPre=-/usr/bin/docker rm %n
ExecStart=/usr/bin/docker run --rm --cpus="4" -m="8g" --name %n \
        -e AZP_URL=${AZP_URL} -e AZP_TOKEN=${AZP_TOKEN} -e AZP_AGENT_NAME=${AZP_AGENT_HOSTNAME}-<Agent-Instance> -e AZP_POOL=${AZP_POOL} \
        -v /var/run/docker.sock:/var/run/docker.sock \
        dockeragent:latest --once

[Install]
WantedBy=default.target

Have you checked the @jcragun's answer? Please check if it meets your requirements. — Ging Yuan-MSFT, Nov 24 '22 at 07:37

score 0 · Accepted Answer · answered Nov 23 '22 at 20:18

0

Consider using a process manager like systemd to do this work outside of the container lifecycle as managed by Docker. See Docker docs for more info. For example:

[Unit]
Description=My Service
After=docker.service
Requires=docker.service

[Service]
TimeoutStartSec=0
Restart=always
ExecStartPre=-/usr/bin/docker exec %n stop
ExecStartPre=-/usr/bin/docker rm %n
ExecStartPre=/usr/bin/docker pull dockeragent:latest
ExecStart=/usr/bin/docker run --rm --name %n \
    -v /var/run/docker.sock:/var/run/docker.sock \
    dockeragent:latest

[Install]
WantedBy=default.target

answered Nov 23 '22 at 20:18

jcragun

2,060
10
8

Thanks, I'll definitely consider and try this. Will let you know, if that worked for my use case. – ochsenbouillon Nov 25 '22 at 07:51
1

Thank you @jcragun, this worked perfectly fine like I was initially intending to do. I just had to slightly adapt ExecStartPre to `ExecStartPre=-/usr/bin/docker stop %n` in order to stop the container itself before starting. – ochsenbouillon Nov 25 '22 at 15:12
Right on. Glad it worked even if modified from my original answer! – jcragun Dec 01 '22 at 05:00

How to automatically restart a Docker container with/from a clean image?

1 Answers1