Load balancing canaries

Is there a way with the native RancherOS HAProxy load balancer to direct most of the traffic to one service, but send a percentage of traffic to a different service? I’m thinking of when I go to move my stormerider/rancher-wordpress-nginx-trusty image and the equivalent Xenial version, which uses a different version of php. It would be helpful to test it first on a subset of the traffic instead of upgrading an entire site all at once.

you could enable server “weight” in the custom haproxy config, like -

backend <name>
    mode http
    balance static-rr
    server web1  weight 20
    server web2  weight 20
    server web3  weight 20
    server web4  weight 5