diff --git a/roles/haproxy/templates/haproxy.cfg b/roles/haproxy/templates/haproxy.cfg
index 222be82584..68b6ac378f 100644
--- a/roles/haproxy/templates/haproxy.cfg
+++ b/roles/haproxy/templates/haproxy.cfg
@@ -224,11 +224,13 @@ listen  openqa 0.0.0.0:10044
 
 listen  pdc 0.0.0.0:10045
     balance hdr(appserver)
+    # This makes haproxy set a cookie with the server the client used
+    # before. This is used to make sure the same client always goes to
+    # the same server (if it is up), because mod_auth_mellon wants a
+    # local state for now.
+    cookie SERVERID insert indirect nocache
     server  pdc-web01 pdc-web01:80 check inter 10s rise 1 fall 2
-## pdc-web02 is commented out 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-web02 pdc-web02:80 check inter 10s rise 1 fall 2
     option  httpchk GET /rest_api/v1/
     timeout server 3600000
     timeout connect 3600000