I have trouble on my F5 and I have a question: what is the behaviour of LTM if pool is marked down for all members? does he accept new connections with round robin lb?
I know my service is up but I have issue with monitoring on F5 when I have CPU peaks on IT (mysqld process).
When a pool member is marked down bigip will not open any new connections to it. Also, by default, bigip does not close any open connections to a down pool member (this behavior can be changed with the pool setting "action on service down").
When all pool members are down (red diamond status) then the pool and virtual server will also be marked down. A down virtual server will still accept connections and requests. This allows bigip to send a redirect (for http) or respond to client in some way (for example using an irule to provide an http response "Site is temporarily unavailable"). The down virtual server will process requests but they are not sent to any down pool members.
My understanding is as follows... (Tested with BIG-IP v14.0) If a monitor marks all pool members in a pool down (offline for traffic processing - red diamond), then the pool is also marked down, as is any associated virtual server that uses that pool exclusively (meaning it has no other pool it can use for load balancing).
If the virtual server has more than just the one downed pool available for load balancing, perhaps via an iRule or a Local Traffic Policy (or a combination of default pool and an iRule or Local Traffic Policy) then the virtual server will not be marked down. However, any persistent or new connections to the virtual server that wind up being directed to the downed pool (either via the iRule, Local Traffic Policy, or default pool configuration) will fail.
No new or persisting connections are allowed to a virtual server that is marked down (red diamond). Existing connections to the virtual server and downed pool members may or may not complete normally, depending on what the underlying problem is that caused the monitor to mark the pool members down to begin with.