XtraDB Cluster+HAProxy

What method should be used to separate read vs write traffic for xtradb cluster with HAProxy setup. Is it ok to introduce mysql-proxy in this setup ?

You are using Percona XtraDB Cluster so why do you want to separate read and write?
XtraDB Cluster and HAProxy are an amazing combination.

Based on the example ha-proxy configuration, I could see the usage to send writes to the single-host mode (example port 3306) and reads to the entire cluster (example port 3307). Then the cluster behavior is transparent to the original application and still somewhat optimized.