Fetch and store current valid configuration from Proxy

[mlavacca]

Is there an existing issue for this?

• I have searched the existing issues

Problem Statement

#4205 enabled the Kong configuration store and push mechanism by caching the last valid configuration and pushing it to the proxy when the current configuration is broken, and the proxy has no good configuration loaded.

When the current configuration is broken, and KIC restarts for whatever reason, however, there are no means to restore the last good configuration from the controller itself, as the last previous good one was stored in KIC's memory.

Proposed Solution

To overcome the issue described above, when KIC has no previous good configuration stored in memory, we can fetch the good configuration from the proxy (if any) and store it. In this way, we basically treat Kong as the source of truth when all the last good config handlers are lost.

Additional information

This approach should be limited to dbless-mode only, as it is no possible to fetch the last good configuration in db-mode.

Acceptance Criteria

• When KIC has no last good configuration stored, and there is a Kong proxy pod with a good configuration loaded, KIC is able to fetch it and cache it as the last good one.