I'm running Nginx on Kubernetes.
When I use the following proxy_pass directive it works as expected:
proxy_pass "http://service-1.default";However the following does not work:
set $service "service-1";
proxy_pass "http://$service.default";I get an error saying no resolver defined to resolve service-1.default
As far as I can tell proxy_pass is receiving the exact same string so why is it behaving differently?
I need to use a variable because I'm dynamically getting the service name from the URL using a regex.
I've found the reason and a solution.
Nginx detects if a variable is being used in proxy_pass (I don't know how it does that). If there is no variable it resolved the hostname at startup and caches the IP address. If there is a variable it uses a resolver (DNS server) to lookup the IP at runtime.
So the solution is to specify the Kube DNS server like this:
resolver kube-dns.kube-system.svc.cluster.local valid=5s;
set $service "service-1";
proxy_pass "http://$service.default.svc.cluster.local";Note that the full local DNS name of the service must be used which you can get by running nslookup service-1.