haproxy cookie can't roundrobin?

Question

I want do like this,look my haproxy:

backend app
balance     roundrobin
cookie  ha_gray_cookie insert indirect nocache
server  app1 127.0.0.1:5001 cookie 110 check
server  app2 127.0.0.1:5002 cookie 110 check
server  app3 127.0.0.1:5003 cookie 110 check
server  app4 127.0.0.1:5004 cookie 120 check
server  app5 127.0.0.1:5005 cookie 120 check
server  app6 127.0.0.1:5006 cookie 120 check
server  app7 127.0.0.1:5007 cookie 120 check
server  app8 127.0.0.1:5008 cookie 120 check
server  app9 127.0.0.1:5009 cookie 120 check

when users come to here,this has 3/9 chance to visit the new versions(5001 5002 5003) and 6/9 chance to visit the old versions.

above config has some problems, namely that when I set cookie to 110, and then client always visits app1, when I set cookie to 120 then client always visits app4.

I want do this: If I set cookie to 110, client can visit all 3 servers (5001,5002,5003) by roundrobin

Answer 1

The cookie keyword is for stickiness to a particular server, so haproxy won't fall back to round robin like you expect.

Instead, you can create two backends, one with your 110 servers and another with your 120 servers. Use an ACL to direct traffic to either backend based on cookie. Something like this:

frontend cookie_balancer
    bind    :80
    mode    http

    acl is_110 hdr(Cookie) 110
    acl is_120 hdr(Cookie) 120

    use_backend backend_110 if is_110
    use_backend backend_120 if is_120

    default_backend backend_110

backend backend_110
        balance roundrobin
        server  app1 127.0.0.1:5001 check
        server  app2 127.0.0.1:5002 check
        server  app3 127.0.0.1:5003 check

backend backend_120
        balance roundrobin
        server  app4 127.0.0.1:5004 check
        # ...

See:

Using ACLs documentation.

hdr, hdr_sub, or hdr_beg documentation, which you can use to check for a particular cookie and direct traffic accordingly.