HAProxy load balancing with sticky sessions based on request body

Integrating systems you have no influence on needs a lot of workarounds. Recently we could not scale Python service consuming SOAP messages with a new hardware. It just didn’t benefit from more processing cores. On the other hand (and this happens often with older software) setting up several instances gave almost linear scalability. Only thing left – configure a loadbalancer and we are done.

Easier said than done. We had to make sure messages are loadbalanced but also that all messages related to given customer USSD conversation always hit the same backend service. So, we had to use application layer information to configure sticky sessions. This is not straightforward in HAProxy when you have to look into http payload and parse some specific information. We used HAProxy 1.6 and simple LUA script to do just that:

core.Alert("LUA script parsing SOAP element loaded");

function parseElement(txn, salt)

    local payload = txn.req:dup()

    -- parses integer value from element named "element"
    local value = string.match(string.match(payload, "element>%d+<"), "%d+")
    core.Info("value: " .. value)
    return value
end

-- register HAProxy "fetch"
core.register_fetches("parseElement", parseElement)

Put this script into a file and it can be loaded in HAProxy configuration using lua-load directive.

Script registers new HAProxy fetch which can be used to configure session stickiness.

balance roundrobin
stick-table type string size 30k expire 30m
stick on "lua.parseElement" table nodes

You have to also make sure all payload is loaded before you start parsing it. This can be achieved with option http-buffer-request configuration directive.

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New HTTP Logger Grails plugin

I've wrote a new Grails plugin - httplogger. It logs:

  • request information (url, headers, cookies, method, body),
  • grails dispatch information (controller, action, parameters),
  • response information (elapsed time and body).

It is mostly useful for logging your REST traffic. Full HTTP web pages can be huge to log and generally waste your space. I suggest to map all of your REST controllers with the same path in UrlMappings, e.g. /rest/ and configure this plugin with this path.

Here is some simple output just to give you a taste of it.

17:16:00,331 INFO  filters.LogRawRequestInfoFilter  - 17:16:00,340 INFO  filters.LogRawRequestInfoFilter  - 17:16:00,342 INFO  filters.LogGrailsUrlsInfoFilter  - 17:16:00,731 INFO  filters.LogOutputResponseFilter  - >> #1 returned 200, took 405 ms.
17:16:00,745 INFO filters.LogOutputResponseFilter - >> #1 responded with '{count:0}'
17:18:55,799 INFO  filters.LogRawRequestInfoFilter  - 17:18:55,799 INFO  filters.LogRawRequestInfoFilter  - 17:18:55,800 INFO  filters.LogRawRequestInfoFilter  - 17:18:55,801 INFO  filters.LogOutputResponseFilter  - >> #2 returned 404, took 3 ms.
17:18:55,802 INFO filters.LogOutputResponseFilter - >> #2 responded with ''

Official plugin information can be found on Grails plugins website here: http://grails.org/plugins/httplogger or you can browse code on github: TouK/grails-httplogger.