Check that the migrations have been correctly applied at server startup

[vxgmichel]

We probably should never run a given version of the parsec server when the full list of available migrations have not been applied.

Best case scenario, the server will loudly fail when starting to process new requests. Worst case scenario, we won't know about it until a specific situation occurs. Very worst case scenario, data is updated in a way that makes the tables inconsistent, without explicitly failing

Fixing this can easily be done by checking the migration table and comparing it to the available migrations.

The problem is that scalingo tries to run the freshly deployed app and rolls back to the previous version if it fails.

There are several solutions:

• Configure scaling to run the migration automatically after a new deployment
• Force scalingo to accept the new app even it fails due to migrations not being applied
• Automatically apply migrations when starting the parsec server (possibly enabled through an dedicated option)

[FirelightFlagboy]

@touilleMan indicated that postdeploy may be a solution for us, we need to investigate if this solution satisfy us.

[touilleMan]

Having a check on the datamodel version at server startup seems a good improvement.

Automatically apply migrations when starting the parsec server (possibly enabled through an dedicated option)

I'm strongly opposed to this given it may lead to migration being applied on the wrong database (e.g. when running a cli command on the wrong database).

We most likely want to rely on postdeploy hook

The trick is postdeploy is done after the new server version is deployed (and shouldn't crash). So in this scenario we cannot do a check on the datamodel version.

So a possibility would be:

• On startup Parsec server, connects to the database and checks the version of the datamodel.
• If the version is wrong, Parsec server stops with an error message indicating a migration is needed.
• This check can be disabled for when the server is run in a PAAS scenario where the deploy is done before the migration