TIL that you can run a command in a docker container without it explicitly running.

The Use Case

I had a docker container that what restarting at startup because it did not have the required SQL tables needed to run. I had a script that would run the migration files after the container started, but that does not work for a fresh install.

The Trials

Attempt #1: Use `docker exec` to enter the container and run the required migration script.

Result: This failed because the container was still continuously restarting.

Attempt #2: Try to extract the scripts from the container to run externally.

Result: this failed because the container would not stay running long enough to successfully mount a volume.

Attemp #3: Use `docker run —entrypoint` to change the startup script.

Result: Success! I was able to have docker to start the container and run the migration script inside.

Example

docker run \
  --rm \
  --entrypoint <CMD> \
  <ImageName>:<Tag> <CMD ARGS>

In this specific case, I was able to have yarn run a prisma:deploy script

docker run \
  --rm \
  --env-file $SWD/api.env \
  --env-file $SWD/apiMigration.env \
  --entrypoint yarn \
  $IMAGENAME:$TAG prisma:deploy || exit 1

This allowed me to greatly simplify my container deployment workflow and have data migrations happen before the actual codebase needed to run.