7010bdb09c
AT-AT needs to be able to track which user tasks failed and why. To accomplish this we: - Enabled Celery's results backend, which logs task results to a data store; a Postgres table, in our case. (https://docs.celeryproject.org/en/latest/userguide/tasks.html#result-backends) - Created tables to track the relationships between the relevant models (Environment, EnvironmentRole) and their task failures. - Added an `on_failure` hook that tasks can use. The hook will add records to the job failure tables. Now a resource like an `Environment` has access to it task failures through the corresponding failure table. Notes: - It might prove useful to use a real foreign key to the Celery results table eventually. I did not do it here because it requires that we explicitly store the Celery results table schema as a migration and add a model for it. In the current implementation, AT-AT can be agnostic about where the results live. - We store the task results indefinitely, so it is important to specify tasks for which we do not care about the results (like `send_mail`) via the `ignore_result` kwarg.
Generic single-database configuration.