Add a PoolAvailableRule to easily add backup pools #7140
This adds the PoolAvailableRule. Can be used to apply different pools based on availability.
I've added documentation and did some basic testing using this to check correct behavior in case of up:
And this to see if it works properly when a pool is down:
I tested it in following configuration:
Then I manually disabled all three servers in default pool:
And all requests were redirected to backup one:
Then I returned one of the servers to active status and it worked well tool: