These examples teach you to discover and access services with Service Discovery.
We are using a Minikube installation to run the examples. For details, please refer to the installation instructions.
The examples here expect that you have an Ingress controller and a load balancer enabled. For Minikube, you can allow both with
minikube addons enable ingressAnd in a separate terminal, start a minikube tunnel. The following call will create the tunnel in the foreground. You can stop it with CTRL-C.
minikube tunnelWe are using our random-generator application as the deployment we want to expose.
So, first, we are exposing this service with four replicas:
kubectl apply -f https://k8spatterns.io/ServiceDiscovery/deployment.ymlNow let’s create a simple service that dispatches to these four pods dynamically:
kubectl apply -f https://k8spatterns.io/ServiceDiscovery/service.ymlThis service is called ClusterIP, so only reachable from within the cluster.
You can verify this by calling kubectl get svc.
Let’s verify that this service can be reached from within the cluster. For this, let’s create a debug satellite Pod, wait until it’s ready, and then jump into it.
kubectl run dbg --image=k8spatterns/curl-jq --command -- sleep infinity && \
kubectl wait --for=condition=Ready pod/dbg && \
kubectl exec -it dbg -- ashNow do some checks:
# Check DNS entry
dig random-generator.default.svc.cluster.local# Curl to service `random-generator.`
curl -s http://random-generator:8080 | jq .You can also check whether the service coordinates are exposed via environment variables within the pods:
# Check for exposed service variables in our test Pod
env | grep RANDOMLet’s jump out of the debug container with the following command (or CTRL-D)
exitAfter you leave the Pod, let’s switch to NodePort as the service type.
# Update service to type NodePort
kubectl apply -f https://k8spatterns.io/ServiceDiscovery/service-with-nodeport.ymlYou can check the assigned node port with
kubectl get svc random-generatorTo access the URL, we need to start another tunnel in the background and store the access URL in a temporary file.
minikube service random-generator --url > /tmp/random-url.txt &Now we can access our service from the outside of the cluster, namely from your desktop’s shell:
# Pick the URL from the service tunnel and curl it
curl -s $(cat /tmp/random-url.txt) | jq .Stop the tunnel by bringing it back to the foreground with fg and then stop with CTRL-C.
# Update service to type LoadBalancer
kubectl apply -f https://k8spatterns.io/ServiceDiscovery/service-with-loadbalancer.ymlIf your cluster provides a load balancer, you will get the load balancer’s IP when looking at it with kubectl get service. Otherwise, the field EXTERNAL IP will stay in status <pending>.
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Note
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As mentioned previously, for Minikube, start minikube tunnel to add some routing from your localhost to the Minikube IP.
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When Kubernetes has assigned an external IP address to your service (check with kubectl get service), you can query it via this IP address and the service’s port:
# Pick port from the service definition and curl
ip=$(kubectl get svc random-generator -o jsonpath={.status.loadBalancer.ingress[0].ip})
curl -s http://$ip:8080 | jq .Finally, let’s have a look at an Ingress exposed service.
First, we reset our service back to type ClusterIP:
kubectl delete service random-generator
kubectl apply -f https://k8spatterns.io/ServiceDiscovery/service.ymlNext, let’s create the Ingress object with
kubectl apply -f https://k8spatterns.io/ServiceDiscovery/ingress.ymlAs usual, you can check the create Ingress object with kubectl get ingress. Note that you should now have an ADDRESS assigned if your cluster has an ingress controller running.
Since the ingress controller is exposed on port 80, you must restart the minikube tunnel in the other terminal. After restart, it needs to expose a privileged port and will ask you about your administrator password.
After restarting the tunnel, you can now query our internal service over this ingress via localhost port 80:
curl -s http://localhost/