Category: Kev’s Blog

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Updating rke created Kubernetes cluster from 1.11.3 to 1.11.5

There was a vulnerability found today in some older Kubernetes versions. There are already patched versions available. If you have 1.11.3 installed from rke, you can update to 1.11.5 by editing your cluster.yml, replacing the kubernetes image:

kubernetes: rancher/hyperkube:v1.11.3-rancher1

with

kubernetes: rancher/hyperkube:v1.11.5-rancher1

And then run ‘rke up’ again.

This is from this Github ticket.

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The best way to learn anything new in software development is to try it out yourself

You can read books, watch YouTubes and listen to as many podcast as you like, but the best way to learn anything new in software development is to try it out for yourself. Why? Because you’ll learn far more from the hands-on experimentation with a new tech/library/api when you try to use it that can ever be transferred as knowledge and experience from a single book/video/article/podcast. What you can learn from a single 1 hour podcast can give you a high level overview of a topic, but you can never learn as much as you will from trying it our yourself.

Part of the learning experience is working out how to solve the problems you run into. The ‘huh, it never said that in the manual’ experience. Once you’ve worked through the unexpected issues along the way, you’ll have built a much deeper understanding of what it actually takes to use a new technology. It’s where the rubber meets the road that counts.

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Kubernetes Rolling Updates: implementing a Readiness Probe with Spring Boot Actuator

During a Rolling Update on Kubernetes, if a service has a Readiness Probe defined, Kubernetes will use the results of calling this heathcheck to determine when updated pods are ready to start accepting traffic.

Kubernetes supports two probes to determine the health of a pod:

  • the Readiness Probe: used to determine if a pod is able to accept traffic
  • the Liveliness Probe: used to determine if a pod is appropriately responding, and if not, it will be killed and a new pod restarted

Spring Boot’s Actuator default healthcheck to indicate if a service is up and ready for traffic can be used for a Kubernetes Readiness Probe. To include in an existing Spring Boot service, add the Actuator maven dependency:

<dependency>
  <groupId>org.springframework.boot</groupId
  <artifactId>spring-boot-starter-actuator</artifactId
</dependency>

This adds the default healthcheck accessible by /actuator/health, and returns a 200 (and json response { “status” : “up”} ) if the service is up and running. 

To configure Kubernetes to call this Actuator healthcheck to determine the health of a pod, add a readinessProbe section to the container spec section for your deployment.yaml:

spec:
  containers:
  - name: exampleservice-b 
    image: kevinhooke/examplespringboot-b:latest
    imagePullPolicy: Always
    ports:
    - containerPort: 8080
    readinessProbe:
      httpGet:
        path: /example-b/v1/actuator/health
        port: 8080
      initialDelaySeconds: 5
      timeoutSeconds: 5

Kubernetes will call this endpoint to check when the pod is deployed and ready for traffic. During a rolling update, as new pods are created with an updated image, you’ll see their status go from 0/1 available to 1/1 available as soon as the Spring Boot service has completed startup and the healthcheck is responding.

The gif below shows deployment of an update image to a pod. Notice how as new pods are created, they move from 0/1 to 1/1 and then when they are ready, the old pods are destroyed:

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