NGINX environment-based routing

Question

I have a single application running in multiple K8s clusters; Let's say there is a frontend service, and two backend ones.

I use NGINX proxy the requests from the frontend to the backend services. Regular NGINX edition, not NGINX+. Here is the nginx.conf:

server {
    ....
    set $back1 "<k8s hostname for the backend1 service>";
    set $back2 "<k8s hostname for the backend2 service>";

    location /back1 {
        rewrite ^/back1/(.*)$ /$1  break;
        proxy_pass http://$back1;
    }
    
    <and same for the backend 2 service>
}

So basically, what happens is that in my frontend application, I set the backend service address to localhost/back1 and localhost/back2, the requests hit NGINX which strips off those back1 and back2 prefixes and call whatever endpoint I specify after in the actual backend services in K8s.

As I have multiple K8s clusters, the backend services hostnames differ, and I need to account for that in my NGINX conf.

The question is: Is there a way for NGINX to differentiate between my K8s clusters? Perhaps I can pass an environment variable to the container running my frontend service, and make an if statement in nginx.conf. Something like:

server {
    if (${env} = "cluster1") {
        set $back1 = "<cluster1 hostname>"
    }
    if (${env} = "cluster2") {
        set $back1 = "<cluster2 hostname>"
    }
}

Or if I can execute a shell command in the nginx conf to get the hostname and write similar if blocks.

I would appreciate any help on this matter!

Answer 1

I went a different route - via templates, environment variables, and envsubst utility which is shipping in the latest nginx docker images.

In template:

set $upstream_back1 "${BACK1}";
set $upstream_back2 "${BACK2}";

In Dockerfile

RUN envsubst < yourtemplate > /etc/nginx/nginx.conf