Mount a volume in docker-compose conditionally

Question

I have a docker-compose.yml configuration. One of the containers there is a Tomcat server and it has some default .war file deployed in webapps directory.

I want to have the ability to pass (override) the war archive to be deployed by some which resides on the host machine. I think the best would be to have ability somehow switch / override starting docker-compose: as a default, I want to run the webapp (war file) which is inside the container, but I want to have a possibility to mount a directory from my host (for example during development / debugging) if need be.

Currently, I have the following line in my docker-compose.yml, which is commented out if I need the default.

volumes:
# By default, there is the latest version of the application already present in the container
# If you want to provider the container with your own .war file, uncomment the following line
# - ./application/webapps:/usr/local/tomcat/webapps

Is there a better way how to achieve that?

Answer 1

Instead of (not) mounting a volume commenting out that line, I would use https://docs.docker.com/compose/extends/#example-use-case to run a service extension that specifies a volume.

I do this to tackle two different problems:

• I don't specify a volume when the docker image is meant to run in production and has all the necessary files bundled in it.
• I specify a volume during development, to check live changes.

Answer 2

Let's say that the .war filename is "app.war"... you could overwrite it using a env variable like this:

volumes:
 - ./application/webapps/${APPLICATION_ENV}.war:/usr/local/tomcat/webapps/app.war

Then when you need to run a different war file just change the APPPLICATION_ENV value to the one you need to run and restart the container.

I don't think docker-compose does have "conditional volumes", but that way you could change the app.war according with your environment.

Other way would be running a script after the docker-compose up/start to overwrite it, and do it only when needed, like:

docker-compose exec your-container-name cp /a/volume/path/app.war /usr/local/tomcat/webapps/app.war