When multiple servers are available as next-hop proxies for routing requests, the next-hop proxy module can use several modes to call them: Round-robin, failover, and stickiness.
Round-robin mode for next-hop proxies
When routing a request in round-robin mode, the next-hop proxy module calls the next-hop proxy that is next on the list to the one that was called last time.
For the next request, this is handled in the same way, so all servers on the list will eventually have been used as next-hop proxies.
The following diagram shows a next-hop proxy configuration in round-robin mode.
The round-robin mode is configured as part of the settings for next-hop proxies.
Failover mode for next-hop proxies
When routing a request in failover mode, the next-hop proxy module calls the first next-hop proxy on the list.
If this next-hop proxy fails to respond, the call is repeated until the configured number of retries is reached. Only then is the second next-hop proxy in the list tried. It is called in the same way as the first, and eventually, the third next-hop proxy in the list is tried.
This is continued until a next-hop proxy responds or all next-hop proxies in the list were found to be unavailable.
The following diagram shows a next-hop proxy configuration in failover mode.
The failover mode is configured as part of the settings for next-hop proxies.