kubernetes dns resolver in nginx

Question

I was developing locally in docker-compose, and had an nginx container doing a simple proxy_pass like so:

location /app/ {
    proxy_pass http://webapp:3000/;

    proxy_http_version 1.1;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection 'upgrade';
    proxy_set_header Host $host;
    proxy_cache_bypass $http_upgrade;

    resolver 127.0.0.11;
}

I now want to move over to kubernetes in GKE, and the last line is giving me troubles.

I tried to switch the resolver to:

    resolver kube-dns;

I also tried various other IPs and names, but I keep getting an error along the lines of:

nginx: [emerg] host not found in resolver "kube-dns"

My kubernetes setup is that I have a single pod, with 2 containers: 'webapp' and 'nginx'. I simply want to have an external service pointing to nginx that can proxy_pass to webapp.

Any ideas?

score 22 · Answer 1 · answered Oct 25 '18 at 12:34

22

You have to specify the FQDN for the kube-dns and the services.
For GKE kube-dns standard for example, it would be: kube-dns.kube-system.svc.cluster.local
And if you're on the default namespace with your webapp service, it would be: webapp.default.svc.cluster.local

I know the original question is old, but maybe it helps someone.

answered Oct 25 '18 at 12:34

Robert Keck

221
2
3

So to clarify, FQDN of resolver in nginx config or the actual proxy_pass ? – Lennart Rolland Feb 26 '20 at 01:04
5

resolver kube-dns.kube-system.svc.cluster.local ipv6=off; - this also works on Digital Ocean's Kubernetes – Tobias Gassmann Jul 19 '20 at 13:56
thank you @TobiasGassmann this seems to have fixed my DNS problems with `proxy_pass` – alex_jwb90 May 03 '21 at 15:50

score 1 · Answer 2 · answered Aug 30 '21 at 22:09

Achieved this locally running a cluster using Kind with the below steps:

1. Checking the DNS conf of a running pod

kubectl exec -it <pod name> -- cat /etc/resolv.conf

search default.svc.cluster.local svc.cluster.local cluster.local home
nameserver 10.96.0.10
options ndots:5

2. Specifying the nameserver IP as the Nginx resolver

http {
    server {
        resolver 10.96.0.10 valid=10s;

score 1 · Answer 3 · answered May 09 '22 at 11:36

location /app {
  resolver kube-dns.kube-system.svc.cluster.local;

  proxy_pass http://webapp.default.svc.cluster.local;
}

This configuration with FQDN and explicit resolver (note default and kube-system explicit namespaces) worked for me (webapp is Kuberentes service name)

score 1 · Answer 4 · answered Oct 01 '17 at 01:04

1

If nginx lives inside kubernetes there is no need to set the resolver since it will resolve to the correct spot. if nginx and webapp live in the same namespace you can simply

proxy_pass http://webapp

As long as your service name for the webapp is called webapp and using port 80.

If nginx lives outside then you should use a ingress controll or set the service for the webapp to a nodeport. A nodeport will open the same port on all the nodes so you can load balance between them on the nginx side.

answered Oct 01 '17 at 01:04

Mike

21,910
7
55
79

22

This is not true if you use a variable inside the proxy_pass directive: https://stackoverflow.com/questions/17685674/nginx-proxy-pass-with-remote-addr – Dave May 22 '18 at 20:33
This is NOT correct. – Vishrant Jun 15 '21 at 02:35

kubernetes dns resolver in nginx

4 Answers4