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.<\/p>\n
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<\/a> 1.6 and simple LUA<\/a> script to do just that:<\/p>\n Put this script into a file and it can be loaded in HAProxy configuration using lua-load<\/a> directive.<\/p>\n Script registers new HAProxy fetch which can be used to configure session stickiness.<\/p>\ncore.Alert(\"LUA script parsing SOAP element loaded\");\r\n\r\nfunction parseElement(txn, salt)\r\n\r\n local payload = txn.req:dup()\r\n\r\n -- parses integer value from element named \"element\"\r\n local value = string.match(string.match(payload, \"element>%d+<\"), \"%d+\")\r\n core.Info(\"value: \" .. value)\r\n return value\r\nend\r\n\r\n-- register HAProxy \"fetch\"\r\ncore.register_fetches(\"parseElement\", parseElement)\r\n<\/pre>\n
balance\u00a0roundrobin\r\nstick-table\u00a0type\u00a0string\u00a0size\u00a030k\u00a0expire\u00a030m\r\nstick\u00a0on\u00a0\"lua.parseElement\"\u00a0table\u00a0nodes<\/pre>\n