How to run Nextjs Backend with NextAuth alongside Keycloak in Local Kubernetes

I have the following services deployed to a Kubernetes cluster running locally on my machine:

• Keycloak
• NextJS
• Ingress-nginx

The NextJS app is basic: it uses NextAuth and the NextAuth Keycloak provider to allow the user to log in and view a protected page.

I have configured Keycloak with a realm and a web client. This all works fine.

Both services have ingress configurations:

• Keycloak is available via auth.starter.local
• The NextJS app is available via starter.local

These DNS names are manually configured in my /etc/hosts file to resolve to 127.0.0.1.

When I attempt to log in via the NextJS app (auth.starter.local), I get an error. This is caused because the backend NextJS app is attempting to retrieve the .well-known config from Keycloak at its DNS name, which it cannot resolve inside the Kubernetes cluster.

How do I get this to work? Can I configure Kubernetes coredns somehow to get the domain names to resolve from an inside service?

First thing first, the /etc/hosts on your local machine is not shared nor cascaded to the pods/containers inside your Kubernetes clusters. They each has their own /etc/hosts files. To add custom entries to each of those /etc/hosts inside the pod/container, you need to use HostAliases.

You have to map the auth.starter.local custom domain inside the pod/container of your NextJS app to the IP of the service for the Keycloak. Run a kubectl describe on the service to obtain its IP.

Next, add the HostAliases setting to the deployment of your NextJS app (under .spec.template.spec):

hostAliases:
- ip: "x.x.x.x" # replace with the service's cluster IP
  hostnames:
  - "auth.starter.local"

Repeat in reverse if your Keycloak needs to connect to your NextJS app.