CODEWITHSUNDEEP
docker
Salim Fadhley
Salim Fadhley

Reputation: 8195

Is there a good, standard way to "bootstrap" a containerized application?

I'm working on an application which needs to be initialized the first time it is run.

Practically, what this will do is initialize a database with some starter values, and save some files in a persistent volume. If I stop the container and then restart it, I don't want to re-run that bootstrapping routine. In other words, if the container is present and populated - skip the initialization routine.

The way I was going to implement this was have an entry-point script which checks if the configuration files are present, and if so will skip the bootstrapping routine, however, I was wondering if there is a better way to do it?

For example, is there a way to run a script which is specifically triggered by the need to create a volume? If I could d that, the only circumstance under which I'd run the bootstrapper would be when the application was initializing for the first time.

Or, is there a better, more Dockerish pattern that defines how I should go about this problem?

Upvotes: 0

Views: 165

Answers (1)

David Maze
David Maze

Reputation: 158995

"Do the initialization in an entrypoint script if the files don't already exist" seems to be reasonably idiomatic. For example, the standard postgres:9.6 image checks for a $PGDATA/PG_VERSION file.

Hypothetically this can look something like:

#!/bin/sh
if [ ! -f /data/config.ini ]; then
  /opt/myapp/setup-data.sh /data
fi
exec "$@"

Remember that it's very routine to delete and recreate containers for a variety of reasons (IME stop and start as actions are rare, but some of this is habits born of an earlier age of Docker);this ties well into your intuition to use the entrypoint for this, since it will get launched on every docker run. From within your container you can't really tell if a directory is or isn't a volume and there aren't any hooks you can tie into; at the point the entrypoint begins, the container environment is fully set up, with whatever networks and volumes already attached.

Upvotes: 1

Related Questions