This example demonstrates running pods, replication controllers, and services. It shows two types of pods: frontend and backend, with services on top of both. Accessing the frontend pod will return environment information about itself, and a backend pod that it has accessed through the service. The goal is to illuminate the environment metadata available to running containers inside the Kubernetes cluster. The documentation for the Kubernetes environment is here.
This example assumes that you have a Kubernetes cluster installed and
running, and that you have installed the
kubectl command line tool
somewhere in your path. Please see the getting
started for installation instructions
for your platform.
The code for the containers is under containers/
kubectl create -f ./backend-rc.yaml kubectl create -f ./backend-srv.yaml kubectl create -f ./show-rc.yaml kubectl create -f ./show-srv.yaml
kubectl describe service show-srv to determine the public IP of
Note: If your platform does not support external load balancers, you’ll need to open the proper port and direct traffic to the internal IP shown for the frontend service with the above command
curl <public ip>:80 to query the service. You should get
something like this back:
Pod Name: show-rc-xxu6i Pod Namespace: default USER_VAR: important information Kubernetes environment variables BACKEND_SRV_SERVICE_HOST = 10.147.252.185 BACKEND_SRV_SERVICE_PORT = 5000 KUBERNETES_RO_SERVICE_HOST = 10.147.240.1 KUBERNETES_RO_SERVICE_PORT = 80 KUBERNETES_SERVICE_HOST = 10.147.240.2 KUBERNETES_SERVICE_PORT = 443 KUBE_DNS_SERVICE_HOST = 10.147.240.10 KUBE_DNS_SERVICE_PORT = 53 Found backend ip: 10.147.252.185 port: 5000 Response from backend Backend Container Backend Pod Name: backend-rc-6qiya Backend Namespace: default
First the frontend pod’s information is printed. The pod name and
namespace are retrieved from the
Downward API. Next,
USER_VAR is the name of
an environment variable set in the pod
definition. Then, the dynamic Kubernetes environment
variables are scanned and printed. These are used to find the backend
backend-srv. Finally, the frontend pod queries the
backend service and prints the information returned. Again the backend
pod returns its own pod name and namespace.
Try running the
curl command a few times, and notice what
watch -n 1 curl -s <ip> Firstly, the frontend service
is directing your request to different frontend pods each time. The
frontend pods are always contacting the backend through the backend
service. This results in a different backend pod servicing each
request as well.
kubectl delete rc,service -l type=show-type kubectl delete rc,service -l type=backend-type