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Environment Guide Example

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.

Diagram

Prerequisites

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.

Optional: Build your own containers

The code for the containers is under containers/

Get everything running

kubectl create -f ./backend-rc.yaml
kubectl create -f ./backend-srv.yaml
kubectl create -f ./show-rc.yaml
kubectl create -f ./show-srv.yaml

Query the service

Use kubectl describe service show-srv to determine the public IP of your service.

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

Run 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

Kubenertes 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 retreived 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 service, named 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 changes. Ex: 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.

Cleanup

kubectl delete rc,service -l type=show-type
kubectl delete rc,service -l type=backend-type

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