Force use of a certain subset of backends in haproxy

haproxy

I'm setting up haproxy to use multiple backend servers but want one of them to handle particular requests:

backend bagend
        mode http
        balance roundrobin
        option httpchk GET / HTTP/1.1\r\nHost:\ www.example.com
        use-server app1_00 if { path_beg /frodo }
        use-server app1_01 if { path_beg /frodo }
        use-server app1_02 if { path_beg /frodo }
        use-server app1_03 if { path_beg /frodo }
        server  app1_00 10.0.0.1:9100 check
        server  app1_01 10.0.0.1:9101 check
        server  app1_02 10.0.0.1:9102 check
        server  app1_03 10.0.0.1:9103 check
        server  app2_00 10.0.0.2:9100 check
        server  app2_01 10.0.0.2:9101 check
        server  app2_02 10.0.0.2:9102 check
        server  app2_03 10.0.0.2:9103 check

Will my use-server commands balance across all 4 backends on app1? Or do I need to do this a different way? It looks as though everything is going to app1_00.

Best Answer

What you want to do is have an acl in the frontend send the request to a different backend based on the URL.

frontend shire
    bind *:80
    mode http
    acl path-frodo path_beg /frodo
    use backend longbottom if path-frodo
    default_backend bagend

backend longbottom
    mode http
    balance roundrobin
    option httpchk GET / HTTP/1.1\r\nHost:\ www.example.com
    server  app1_00 10.0.0.1:9100 check
    server  app1_01 10.0.0.1:9101 check
    server  app1_02 10.0.0.1:9102 check
    server  app1_03 10.0.0.1:9103 check

backend bagend
    mode http
    balance roundrobin
    option httpchk GET / HTTP/1.1\r\nHost:\ www.example.com
    server  app1_00 10.0.0.1:9100 check
    server  app1_01 10.0.0.1:9101 check
    server  app1_02 10.0.0.1:9102 check
    server  app1_03 10.0.0.1:9103 check
    server  app2_00 10.0.0.2:9100 check
    server  app2_01 10.0.0.2:9101 check
    server  app2_02 10.0.0.2:9102 check
    server  app2_03 10.0.0.2:9103 check

All request beginning with /frodo will hit only app1_00, app1_01, app1_02 and app1_03. All other requests will hit everything.

Related Solutions

Using HAProxy to balance slow and fast requests across multiple backends

A little from column A, a little from column B :)

For the sake of uptime, you should definitely be using health checks in HAProxy regardless of anything else. If one of your backend nodes goes down, you want HAProxy to stop sending requests to it. The failure doesn't have to be in your application, could be hardware, network, whatever. This is pretty straightforward to configure:

option httpchk GET /test HTTP/1.0\r\n

250ms sounds like a very frequent check. At that rate, your backend servers could spend a lot of time just processing health checks. You need to trade off the cost of the health checks in terms of application overhead vs how quickly you want dead nodes to be taken offline.

The second strategy is one I've used before. Figure out the total number of concurrent connections your application can handle. Then, in HAProxy, split the requests into slow and fast and allocate a proportion of your total connections to each. E.g.,

frontend myfrontend
    bind *:80
    acl url-slow path /some-long-running-request
    use_backend slow-backend if url-slow
    default_backend regular-backend

backend slow-backend
    ...
    server backend1 1.2.3.4:80 maxconn 10

backend regular-backend
    ...
    server backend1 1.2.3.4.:80 maxconn 90

So, say, backend1 can handle 100 concurrent connections. In the above, we allocate 90 connections to 'regular' requests and 10 connections to slow running requests. Even if you use up all of your slow connections, then the 'regular' requests will still be processed.

Good luck!

Serve 404 from HAProxy when no acls match

If you would be okay with any of the following response codes: 200, 400, 403, 405, 408, 429, 500, 502, 503, or 504.

Then you could do something like this:

frontend www
  ...
  default_backend no-match

backend no-match
  mode http
  http-request deny deny_status 400

http-request: http://cbonte.github.io/haproxy-dconv/1.7/configuration.html#4-http-request
Accepted response codes described in errorfile: http://cbonte.github.io/haproxy-dconv/1.7/configuration.html#errorfile

Best Answer

Related Solutions

Using HAProxy to balance slow and fast requests across multiple backends

Serve 404 from HAProxy when no acls match

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