Remove ACR Pull in favor of managing container settings in App Dev CD

[nmiodice]

Description

As an application developer I don't want to rely on ACR Web Hooks to initiate a deployment because it can result in unexpected deployments to production

Acceptance Criteria

• ASE template no longer relies on webhook to deploy
• SR template no longer relies on webhook to deploy
• All existing tests pass
• New tests are written if necessary to assert the correct behavior

Failure modes for ACR webhook & Web App CD

In the following scenarios, assume the following:

• “A” is a webapp. In each scenario it starts as the production slot
• “B” is a webapp. In each scenario it starts as the staging slot

Scenario 1 – Failure to rollback application deployments via swap:

• “A” is running image with image hash “foo”
• “B” is running image with image hash “bar”
• “A” and “B” are swapped
• “A” (now staging) unexpectedly picks up the latest image (“bar”). I’m not sure why.
• Image hash “bar” is determined to have a bug; a rollback is needed and is done by re-swapping the slots
• “A” (now production) is incorrectly running “bar”

Scenario 2 – Production is already down in this case:

• “A” is running a misconfigured container that fails start (i.e., process dies on startup due to bug in application code). App Service will (indefinitely) retry by pulling and deploying until it can startup successfully.
• ACR push occurs; “B” picks up new image
• On a retry attempt, “A” picks up the latest image and it is deployed unexpectedly to production

Scenario 3 – Possibly a very delayed impact:

• “A” is running image with image hash “foo”
• ACR push occurs; “B” is running image with image hash “bar”
• “A” (re)starts for some reason (you can do this via portal, or perhaps a backend server dies, or perhaps the service plan scales out); “A” picks up the latest image and it is deployed unexpectedly to production.

Scenario 4 (low risk) – The first deployment:

• “A” and “B” are newly deployed; No image is running in either slot
• “A” and “B” try to start (indefinitely?) repeatedly
• ACR push occurs; webhook for “B” fires
• On a retry attempt, “A” picks up the latest image and it is deployed unexpectedly to production (note: similar to Scenario 1)

[TechnicallyWilliams]

Once completed, suggested next step for us may be living in user story #313 ([Docs] Document Steps for Container Validation)