docker-compose and Kubernetes examples

This is a very basic Spring Boot app which stores floating point values in a Redis key/value store. To add a value (with the app running on port 8080) using HttpIE:

~ $ http -f post localhost:8080/value/foo?value=10

HTTP/1.1 201
Content-Length: 0
Date: Thu, 03 Jan 2019 21:42:11 GMT

Reading a value back:

~ $  http localhost:8080/value/foo

HTTP/1.1 200
Content-Type: application/json;charset=UTF-8
Date: Thu, 03 Jan 2019 21:42:21 GMT
Transfer-Encoding: chunked

10.0

The app includes the Spring Actuator endpoints, for example:

~ $ http localhost:8080/actuator/health
 
HTTP/1.1 200
Content-Type: application/vnd.spring-boot.actuator.v2+json;charset=UTF-8
Date: Thu, 03 Jan 2019 22:11:25 GMT
Transfer-Encoding: chunked

{
    "status": "UP"
}

If the app is not able to reach Redis, the status will be shown as DOWN.

Running in docker-compose

Build the application jarfile:

mvn clean package

Rebuild the container and start the compose:

docker-compose build
docker-compose up

Note: just docker-compose up should work, however it will not rebuild the application container in all cases. The app will be exposed on port 9999. See docker-compose.yaml for details.

One point to note is that the port forward on the keyvalue service is not necessary for the compose to work; the port would be exposed on the internal network anyway. However forwarding it means that you can connect locally using redis-cli to poke around.

Running on Kubernetes

kubectl apply -f kubernetes/

The Kubernetes deployment uses the Spring Actuator /health endpoint as a readiness probe, the pod will become ready once the connection to Redis is established and the status becomes UP (see above).

To get the URL to access on Minikube:

url=$(minikube service kubebootsvc --url)
http $url/actuator/health
http $url/value/foo

The Kubernetes deploy creates 2 replicas of the pod, and the code adds a custom header X-Pod-IP with the internal IP of the pod that serviced your request (so you can see the load balancing in action):

http $url/value/foo

HTTP/1.1 200 
Content-Type: application/json;charset=UTF-8
Date: Sat, 05 Jan 2019 00:20:20 GMT
Transfer-Encoding: chunked
X-Pod-IP: 172.17.0.10

3.14