When running cloud-native applications in the orchestration framework Kubernetes and the service mesh Istio, microservices need to report whether they are ready and live. Kubernetes needs to know this to restart containers if necessary. Istio needs to know this information to define where to route requests to.
With the Kubernetes livenessProbe it is determined whether, as the name indicates, the pod is live. Pods that are live might not be ready though, for example when they just started and still need to load data. That’s why there is a second readinessProbe.
I’ve implemented some sample code that shows how to develop these health checks with Eclipse MicroProfile.
Get the code of cloud-native-starter from GitHub.
Here is the Java code which returns for the ‘articles’ service that the microservice is ready.
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import org.eclipse.microprofile.health.Health;
import org.eclipse.microprofile.health.HealthCheck;
import org.eclipse.microprofile.health.HealthCheckResponse;
import javax.enterprise.context.ApplicationScoped;
@Health
@ApplicationScoped
public class HealthEndpoint implements HealthCheck {
@Override
public HealthCheckResponse call() {
return HealthCheckResponse.named("articles").withData("articles", "ok").up().build();
}
}
In the Kubernetes yaml file the URLs of the livenessProbe and the readinessProbe are defined.
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kind: Deployment
apiVersion: apps/v1beta1
metadata:
name: articles
spec:
replicas: 1
template:
metadata:
labels:
app: articles
version: v1
spec:
containers:
- name: articles
image: articles:1
ports:
- containerPort: 8080
livenessProbe:
exec:
command: ["sh", "-c", "curl -s http://localhost:8080/"]
initialDelaySeconds: 20
readinessProbe:
exec:
command: ["sh", "-c", "curl -s http://localhost:8080/health | grep -q articles"]
initialDelaySeconds: 40
restartPolicy: Always
If you want to run this demo yourself in Minikube, get the code from GitHub and invoke these commands:
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$ git clone https://github.com/nheidloff/cloud-native-starter.git
$ scripts/check-prerequisites.sh
$ scripts/deploy-articles-java-jee.sh
$ kubectl get pods --watch
$ minikube dashboard
To learn more about health checks, take a look at these articles: