How can I fall back to a different upstream pool when the first fails?

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2

I can use handle_errors to emulate the intended behavior, like the following:

shade-rpc.lavenderfive.com {
		reverse_proxy 5.0.6.1:17157 5.0.6.1:10057 5.0.6.1:10157
        handle_errors {
	       @5xx `{err.status_code} >= 500 && {err.status_code} < 600` {
             reverse_proxy 5.0.6.2:17157 5.0.6.2:10057 5.0.6.2:10157
           }
        }
}

However, the handle_errors page suggests you should use handle_response with reverse_proxy.