Custom routing in load balancer

Question

Is it possible to define a custom routing in NGINX or other Load Balancer? I.e. I have a cookie or a header and based on its value I decide which backend server to choose? I need some very simple logic - values a1,a2,a3 - to server A, values b1,b2 to server B, all other to server C

Answer 1

In nginx you can do it simply by using if:

location / {
    if ($http_cookie  ~* "yourcookiename=a") {
        proxy_pass http://upstream_a;
        break;
    }
    if ($http_cookie ~* "yourcookiename=b") {
        proxy_pass http://upstream_b;
        break;
    }
    proxy_pass http://upstream_c;
}

This is simple regexp , so this way if "yourcookiename" has value a1,a2 etc. it will go to uprstream_a and so on. Hope it helps...

Answer 2

If you need some sticky session, there are open source third party modules that can do that with nginx, while the native implementation is part of the commercial subscription. Also, tengine, an open source chinese fork of nginx developed by Alibaba can do that natively.

If you want to do it the custom way, use a map to avoid processing a chain of if blocks for all requests. This is also better for readability. For instance, using a cookie :

map $cookie_mycookie $node {
    "~^a[1-3]$" "A";
    "~^b[1-2]$" "B";
    default     "C";
}

server {

    location / {
        proxy_pass http://$node;
    }

}