A good Docker entry point

To create a good docker entry point for your image or your container, you must take care of a simple thing. The entry point script must not fail if you run it twice or more.

Indeed, in a container the data is persisted. If you stop and restart a container without removing it, the state/data does not change and can leads to errros.

A bad entry point example.

mv /tmp/nginx/conf.d/default /etc/nginx/conf.d/default
nginx &

What is the problem ?

• The first time the container is started, everything works fine.
• The second time the file /tmp/nginx/conf.d/default no more exists and the mv command generates an error.

To bypass the problem, you can remove the container with docker rm -f container_id|name and restart it.

Conclusion

Test your entry points by executing them twice, at least…