Kubernetes service routing with wildcard DNS and ingress controller

Kubernetes wildcard DNS refers to a DNS configuration that allows for routing any subdomain of a domain to a particular service or set of services within a Kubernetes cluster. A wildcard DNS record is usually indicated by an asterisk (*), for example: *.yourdomain.com.

Using wildcard DNS with Kubernetes has several advantages:

• Without wildcard DNS, each time you deploy a new service and want to expose it with a domain name, you would have to create a new DNS record. With wildcard DNS, any subdomain of yourdomain.com (like service1.yourdomain.com, service2.yourdomain.com, etc.) will automatically resolve to the IP address specified in the wildcard record.
• Wildcard DNS is especially useful for development and staging environments where you might frequently spin up and tear down services. The wildcard DNS ensures that these services get valid DNS names without additional configuration.
• When used in conjunction with an ingress controller (like Nginx or Traefik), wildcard DNS can be powerful. The ingress controller can route traffic based on the hostname, meaning that while the wildcard DNS points all subdomains to the ingress controller, the controller itself determines which service should handle the request based on its configuration.

In short, Kubernetes wildcard DNS, combined with an ingress controller, provides a powerful way to dynamically route external traffic to different services in the cluster based on hostname patterns.

Installing the ingress controller with helm

1. Add the Helm repository:

   helm repo add ingress-nginx https://kubernetes.github.io/ingress-nginx
   helm repo updateCopy

2. Install the Nginx ingress controller using the helm packet manager:

   helm install nginx-ingress ingress-nginx/ingress-nginx \
     --namespace ingress-nginx --create-namespaceCopy

3. Verify the installation:

   kubectl get pods -n ingress-nginxCopy

Configuring wildcard DNS

1. Retrieve the ingress IP:

   kubectl get svc -n ingress-nginxCopy

   Note:

   It may take a few minutes for the Load Balancer IP to be assigned.

2. Configure Wildcard DNS:

   • Go to your DNS provider and add an A record for *.yourdomain.com pointing to the IP address of the ingress controller’s load balancer.

Deploy a sample application

1. Deploy a sample application by creating a file hello-world.yaml. Below is a simple deployment and service example. Copy the content in the file and save it:

   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: hello-world
   spec:
     replicas: 2
     selector:
       matchLabels:
         app: hello-world
     template:
       metadata:
         labels:
           app: hello-world
       spec:
         containers:
         - name: hello-world
           image: nginxdemos/hello
           ports:
           - containerPort: 80
   ---
   apiVersion: v1
   kind: Service
   metadata:
     name: hello-world
   spec:
     ports:
     - port: 80
     selector:
       app: hello-worldCopy

2. Apply the configuration with kubectl apply -f hello-world.yaml

Create an ingress resource

1. Copy the following sample resource and paste and save it into a YAML file called wildcard-ingress.yaml. Remember to replace the domain name with your own.

   apiVersion: networking.k8s.io/v1
   kind: Ingress
   metadata:
     name: wildcard-ingress
     annotations:
       nginx.ingress.kubernetes.io/rewrite-target: /
   spec:
     rules:
     - host: "*.yourdomain.com"
       http:
         paths:
         - path: /
           pathType: Prefix
           backend:
             service:
               name: hello-world
               port:
                 number: 80Copy

2. Apply the configuration with kubectl apply -f wildcard-ingress.yaml

Test your setup

1. Access your application by pointing your web brower to http://anything.yourdomain.com (replace this with your own domain name). It should load the hello-world application.

2. Test with different subdomains, they should all lead to your hello-world application due to the wildcard DNS setup.

You have successfully set up an ingress controller with wildcard DNS on Scaleway Kubernetes Kapsule. This setup will allow you to easily manage multiple subdomains and route traffic to the various services in your Kubernetes cluster.