Wha the best place and when to run heavy db migration?

[vldmr-k]

In all my projects, I run db migration in entrypoints.
For not big db it's enough.

On this week, I migrate big project from directly update project on the server -> kamal.
And this scenario doesn't work well.

What happened?

1. added migration which create new column in big table
2. run this migration in entry-point script.
3. migration start to apply this migration
4. docker start to check is container is healthy
5. after 100 seconds (deploy_timeout:100), docker restart container.

And this unpredictable behavior stuck deployment process.

I see few ways how to resolve this problem:

A. Increasing deploy_timeout, it is not good way.
B Split phase of deployment to kamal build, kamal app exec '<apply migration cmd>', kamal deploy --skip-push
In this method, we have problem with env. Because env on the remove server applying after deployment.
H Apply via hook - never try this method.

What the best scenario to apply heavy migration while deploying applications?

[jdelStrother]

I've used B sometimes - eg

$ kamal build pull -d staging --version latest-staging
$ kamal app exec  -d staging --version latest-staging  --primary -i 'bin/rails db:migrate'

I'm not sure what you mean by "In this method, we have problem with env. Because env on the remove server applying after deployment" - could you clarify?