Reverse proxy: load balance between two servers with third server as backup

[David_Szabo (Dávid Szabó)]

Is it possible to enable load balancing between two servers with a third server as a backup?

Something like lb_policy round_robin but with N number of upstream.
For example, it would be great to specify the first two upstreams, then use the last one when the first two upstreams are unavailable: lb_policy round_robin 2.

Why?
In our case, we have a third server as a backup, but the processing power of this server is worse than the first two production-grade servers. We want to load balance between the first two servers to ensure the best performance.

Example config

reverse_proxy node1 node2 node3 {
  lb_policy round_robin
}

[francislavoie]

Hmm. Good question. That is tricky. Not something we’ve considered before.

I think you could do it like this, kinda awkward though:

example.com {
	reverse_proxy node1 node2 {
		lb_policy round_robin
		# make sure you have health checks enabled
		# otherwise the nodes will never be marked unhealthy
	}

	handle_errors {
		@proxyErr `{err.status_code} in [502, 503]`
		reverse_proxy @proxyErr node3
	}
}

If all the upstreams are unavailable (503) or failed to connect (502) then it will proxy to node3.

[David_Szabo (Dávid Szabó)]

Thank you! I wish it was more elegant though

[matt (Matt Holt)]

Haha I love this, it’s brilliant!