Support multiple gateways connected to different databases

[randmonkey]

Is there an existing issue for this?

• I have searched the existing issues

Problem Statement

Following of #4751. If the Kong admin API service is pointing to a set of Kong pods backed by different databases (different host/port/DB name), KIC needs to choose one client connected to each different DB to keep every instance synced with the latest configuration.

Proposed Solution

• Read host, port and DB name from /configuration admin API endpoint and group clients by the DB ("local" host in different instances should be considered as different hosts)
• When sending config to Kong gateway clients in DB mode, choose one client for each DB

Additional information

No response

Acceptance Criteria

• If multiple Kong gateway instances uses different DBs, their configuration should be synced with KIC.

[rainest]

Does this indeed follow from #4751? AFAIK we've never supported the notion of a single Kong cluster where some instances use one database and others another. DB HA considerations are handled at the DB level, with replica configuration opaque behind a single DB hostname for all Kong instances.

There was some discussion in the distant past re a single controller instance managing separate Kong clusters, but that was in the context of automatically provisioning clusters for multiple incompatible Gateways and sending each its appropriate configuration. I don't think that's what this is trying to tackle, since it's implying the same configuration to both databases.