Summary:
In an emergency, we may want to serve certain documents with "old" workers as we fix problems. This diff adds some support for that.
* Creates duplicate task definitions and services for staging and production doc workers (called grist-docs-staging2 and grist-docs-prod2), pulling from distinct docker tags (staging2 and prod2). The services are set to have zero workers until we need them.
* These new workers are started with a new env variable `GRIST_WORKER_GROUP` set to `secondary`.
* The `GRIST_WORKER_GROUP` variable, if set, makes the worker available to documents in the named group, and only that group.
* An unauthenticated `/assign` endpoint is added to documents which, when POSTed to, checks that the doc is served by a worker in the desired group for that doc (as set manually in redis), and if not frees the doc up for reassignment. This makes it possible to move individual docs between workers without redeployments.
The bash scripts added are a record of how the task definitions + services were created. The services could just have been copied manually, but the task definitions will need to be updated whenever the definitions for the main doc workers are updated, so it is worth scripting that.
For example, if a certain document were to fail on a new deployment of Grist, but rolling back the full deployment wasn't practical:
* Set prod2 tag in docker to desired codebase for that document
* Set desired_count for grist-docs-prod2 service to non-zero
* Set doc-<docid>-group for that doc in redis to secondary
* Hit /api/docs/<docid>/assign to move the doc to grist-docs-prod2
(If the document needs to be reverted to a previous snapshot, that currently would need doing manually - could be made simpler, but not in scope of this diff).
Test Plan: added tests
Reviewers: dsagal
Reviewed By: dsagal
Differential Revision: https://phab.getgrist.com/D2649
Summary: This moves enough server material into core to run a home server. The data engine is not yet incorporated (though in manual testing it works when ported).
Test Plan: existing tests pass
Reviewers: dsagal
Reviewed By: dsagal
Differential Revision: https://phab.getgrist.com/D2552
