When building docker image with GitLab CI, wait until docker daemon starts

background

When I was investigating the cause of moss in Job that builds docker image with GitLab CI, I found that it was moss when I did docker info.

docker is a client-server application, but if you type the docker info command before the docker daemon on the server side starts, you will get angry with" I don't have a daemon ... ".

Cannot connect to the Docker daemon at tcp://docker:2375. Is the docker daemon running?

The docker in docker dind is used correctly, and it's really just a delay in booting, so if you wait like sleep 10, the build will pass. However, I don't want to put on a mysterious sleep, so I want to wait until the daemon starts.

What i did

I wrote a shell script and added it to the project. Fortunately, I know that docker info will fail without daemon, so I will use it.

wait.sh

#!/bin/sh

#A script that waits for the dind docker daemon to start
while :
do
    if docker info > /dev/null 2>&1; then
        break
    fi
    echo 'waiting docker daemon...'
    sleep 1
done

exit 0

Put the script before docker info in .gitlab-ci.yml. Don't forget chmod to make it executable.

yml:.gitlab-ci.yml

before_script:
  - chmod u+x wait.sh && ./wait.sh
  - docker info

result

The build no longer fails because it waits for startup.