diff --git a/roles/haproxy/templates/haproxy.cfg b/roles/haproxy/templates/haproxy.cfg
index 1cd2032b69..7a5df1229a 100644
--- a/roles/haproxy/templates/haproxy.cfg
+++ b/roles/haproxy/templates/haproxy.cfg
@@ -275,14 +275,15 @@ listen  openqa 0.0.0.0:10044
 
 listen  pdc 0.0.0.0:10045
     balance hdr(appserver)
+    # Set session persistence with a cookie.
+    # https://jdennis.fedorapeople.org/doc/rhsso-tripleo-federation/html/rhsso-tripleo-federation.html#step-18-use-proxy-persistence-for-keystone-on-each-controller
+    cookie SERVERID insert indirect nocache
+
 {% if env == "staging" %}
-    server  pdc-web01 pdc-web01:80 check inter 10s rise 1 fall 2
-{% else %}
-## pdc-web01 is absent because we don't currently know how to configure
-## mod_auth_mellon to work when distributed across more than one app node.  It
-## expects to be able to share some state between requests in-process.  Boo.
-    server  pdc-web02 pdc-web02:80 check inter 10s rise 1 fall 2
+    server  pdc-web01 pdc-web01:80 check inter 10s rise 1 fall 2 cookie pdc-web01
 {% endif %}
+    server  pdc-web02 pdc-web02:80 check inter 10s rise 1 fall 2 cookie pdc-web02
+
     option  httpchk GET /rest_api/v1/
     timeout server 3600000
     timeout connect 3600000