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If you have non-trivial migrations to apply, or if two non-local environments (e.g. stage and production) have different migration states, describe your situation in the #django Slack channel and go talk to the Ops team before doing anything else. Similarly, migrations can become complicated when two different people create two different migrations around the same time. When in doubt, post in #django and talk to Ops.
It is often useful to review or provide the SQL generated by a migration. See sqlmigrate doc for details.
Don't revert code that includes migrations, don't change old migrations.
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When using AWS Aurora, a nullable column can be added to existing large (100k rows+?) tables without causing downtime. However, the migration may still timeout in GoCD - so please coordinate the release with DevOps.
- Make a new field addition in model with null=True.
- Generate the model-change migrations locally.
- Create a pull request containing the model change and newly-generated migrations.
- Merge the migration pull request.
- The release process will run the migration and add the nullable column to table.
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On AWS Aurora, indexes can be build on large tables without causing downtime, but this requires devops coordination as the migration may timeout in GoCD.
- Add the new index on model fields.
- Generate the model-change migrations locally.
- Make pull request containing the model change and newly-generated migrations.
- Merge the migration pull request.
- Release will run the migration and add the index to table.
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