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app-deploy-microservices-networking.adoc

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Internal Kubernetes networking

Duration: 7:00

In Kubernetes every pod has a unique IP address! You can “login” into one of these pods by using the kubectl exec command. This can drop you into a shell and execute commands inside of the container.

First, find the name of the both helloworld-service-vertx pods:

[vagrant@rhel-cdk kubernetes]$ kubectl get pods -l app=helloworld-service-vertx
NAME                             READY     STATUS    RESTARTS   AGE
helloworld-service-vertx-?????   1/1       Running   0          14m
helloworld-service-vertx-?????   1/1       Running   0          15m
Note
 Note that we used the parameter -l app=helloworld-service-vertx. This parameter allows us to specify labels as filter. The label app=helloworld-service-vertx was defined in the ReplicationController as a template for all pods.

Then, use kubectl exec to exucute a "bash" process into the container:

[vagrant@rhel-cdk kubernetes]$ kubectl exec -it helloworld-service-vertx-????? bash
[jboss@helloworld-service-vertx-????? ~]$ _

You are now in a shell inside of the helloworld-service-vertx container. You can run ps, and hostname:

[jboss@helloworld-service-vertx-edux9 ~]$ ps aux
USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
jboss        1  0.2  1.7 2691876 51696 ?       Ssl  20:24   0:02 java -Xmx256m -
jboss       22  0.1  0.0  11772  1832 ?        Ss   20:40   0:00 bash
jboss       38  0.0  0.0  47424  1656 ?        R+   20:41   0:00 ps aux

[jboss@helloworld-service-vertx-edux9 ~]$ hostname  -i
172.17.0.7

[jboss@helloworld-service-vertx-edux9 ~]$ exit
exit

Don’t forget to exit :).

Try it with another the other pod and see its IP address.

[vagrant@rhel-cdk kubernetes]$ kubectl exec -it helloworld-service-vertx-????? bash

[jboss@helloworld-service-vertx-????? ~]$ hostname
helloworld-service-vertx-?????

[jboss@helloworld-service-vertx-????? ~]$ hostname -i
172.17.0.8

[jboss@helloworld-service-vertx-????? ~]$ exit

Since we are running two instances of the Hello World Service (one instance in one pod), and that the IP addresses are not only unique, but also ephemeral - how will a client reach our services? We need a way to discover the service.

In Kubernetes, Service Discovery is a first class citizen. We created a Service that will:

  • act as a load balancer to load balance the requests to the pods, and

  • provide a stable IP address, allow discovery from the API, and also create a DNS name!

If you login into a container (find and use the frontend-ui container), you can access the helloworldservice via the DNS name:

[vagrant@rhel-cdk kubernetes]$ kubectl exec -it frontend-ui-????? bash

bash-4.2$* wget -qO- http://helloworld-service-vertx:8080/api/hello/Rafael*
Hello Rafael from helloworld-service-vertx-a4zq3 with 1.0

bash-4.2$ exit
exit

Pretty simple right!?