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‎docs/user-guide/environment-guide/index.md‎

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title: Using Environment Variables
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---
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This example demonstrates running pods, replication controllers, and
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services. It shows two types of pods: frontend and backend, with
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services on top of both. Accessing the frontend pod will return
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environment information about itself, and a backend pod that it has
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accessed through the service. The goal is to illuminate the
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environment metadata available to running containers inside the
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Kubernetes cluster. The documentation for the Kubernetes environment
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is [here](/docs/user-guide/container-environment).
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![Diagram](/images/docs/diagram.png)
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## Prerequisites
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This example assumes that you have a Kubernetes cluster installed and
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running, and that you have installed the `kubectl` command line tool
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somewhere in your path. Please see the [getting
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started](/docs/getting-started-guides/) for installation instructions
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for your platform.
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## Optional: Build your own containers
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The code for the containers is under
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[containers/](/docs/user-guide/containers/)
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## Get everything running
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```shell
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kubectl create -f ./backend-rc.yaml
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kubectl create -f ./backend-srv.yaml
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kubectl create -f ./show-rc.yaml
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kubectl create -f ./show-srv.yaml
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```
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## Query the service
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Use `kubectl describe service show-srv` to determine the public IP of
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your service.
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> Note: If your platform does not support external load balancers,
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you'll need to open the proper port and direct traffic to the
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internal IP shown for the frontend service with the above command
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Run `curl <public ip>:80` to query the service. You should get
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something like this back:
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```shell
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Pod Name: show-rc-xxu6i
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Pod Namespace: default
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USER_VAR: important information
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Kubernetes environment variables
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BACKEND_SRV_SERVICE_HOST = 10.147.252.185
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BACKEND_SRV_SERVICE_PORT = 5000
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KUBERNETES_RO_SERVICE_HOST = 10.147.240.1
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KUBERNETES_RO_SERVICE_PORT = 80
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KUBERNETES_SERVICE_HOST = 10.147.240.2
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KUBERNETES_SERVICE_PORT = 443
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KUBE_DNS_SERVICE_HOST = 10.147.240.10
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KUBE_DNS_SERVICE_PORT = 53
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Found backend ip: 10.147.252.185 port: 5000
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Response from backend
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Backend Container
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Backend Pod Name: backend-rc-6qiya
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Backend Namespace: default
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```
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First the frontend pod's information is printed. The pod name and
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[namespace](https://github.com/kubernetes/kubernetes/blob/{{page.githubbranch}}/docs/design/namespaces.md) are retrieved from the
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[Downward API](/docs/user-guide/downward-api). Next, `USER_VAR` is the name of
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an environment variable set in the [pod
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definition](/docs/user-guide/environment-guide/show-rc.yaml). Then, the dynamic Kubernetes environment
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variables are scanned and printed. These are used to find the backend
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service, named `backend-srv`. Finally, the frontend pod queries the
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backend service and prints the information returned. Again the backend
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pod returns its own pod name and namespace.
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Try running the `curl` command a few times, and notice what
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changes. Ex: `watch -n 1 curl -s <ip>` Firstly, the frontend service
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is directing your request to different frontend pods each time. The
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frontend pods are always contacting the backend through the backend
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service. This results in a different backend pod servicing each
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request as well.
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## Cleanup
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```shell
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kubectl delete rc,service -l type=show-type
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kubectl delete rc,service -l type=backend-type
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```
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This example demonstrates running pods, replication controllers, and
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services. It shows two types of pods: frontend and backend, with
9+
services on top of both. Accessing the frontend pod will return
10+
environment information about itself, and a backend pod that it has
11+
accessed through the service. The goal is to illuminate the
12+
environment metadata available to running containers inside the
13+
Kubernetes cluster. The documentation for the Kubernetes environment
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is [here](/docs/user-guide/container-environment).
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![Diagram](/images/docs/diagram.png)
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## Prerequisites
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This example assumes that you have a Kubernetes cluster installed and
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running, and that you have installed the `kubectl` command line tool
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somewhere in your path. Please see the [getting
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started](/docs/getting-started-guides/) for installation instructions
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for your platform.
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## Optional: Build your own containers
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These are the configuration files for the containers:
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* [backend-rc.yaml](https://raw.githubusercontent.com/kubernetes/kubernetes.github.io/master/docs/user-guide/environment-guide/backend-rc.yaml)
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* [backend-srv.yaml](https://raw.githubusercontent.com/kubernetes/kubernetes.github.io/master/docs/user-guide/environment-guide/backend-srv.yaml)
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* [show-rc.yaml](https://raw.githubusercontent.com/kubernetes/kubernetes.github.io/master/docs/user-guide/environment-guide/show-rc.yaml)
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* [show-srv.yaml](https://raw.githubusercontent.com/kubernetes/kubernetes.github.io/master/docs/user-guide/environment-guide/show-srv.yaml)
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## Get everything running
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```shell
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kubectl create -f ./backend-rc.yaml
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kubectl create -f ./backend-srv.yaml
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kubectl create -f ./show-rc.yaml
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kubectl create -f ./show-srv.yaml
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```
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## Query the service
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Use `kubectl describe service show-srv` to determine the public IP of
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your service.
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> Note: If your platform does not support external load balancers,
50+
you'll need to open the proper port and direct traffic to the
51+
internal IP shown for the frontend service with the above command
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Run `curl <public ip>:80` to query the service. You should get
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something like this back:
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```shell
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Pod Name: show-rc-xxu6i
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Pod Namespace: default
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USER_VAR: important information
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Kubernetes environment variables
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BACKEND_SRV_SERVICE_HOST = 10.147.252.185
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BACKEND_SRV_SERVICE_PORT = 5000
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KUBERNETES_RO_SERVICE_HOST = 10.147.240.1
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KUBERNETES_RO_SERVICE_PORT = 80
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KUBERNETES_SERVICE_HOST = 10.147.240.2
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KUBERNETES_SERVICE_PORT = 443
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KUBE_DNS_SERVICE_HOST = 10.147.240.10
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KUBE_DNS_SERVICE_PORT = 53
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Found backend ip: 10.147.252.185 port: 5000
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Response from backend
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Backend Container
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Backend Pod Name: backend-rc-6qiya
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Backend Namespace: default
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```
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First the frontend pod's information is printed. The pod name and
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[namespace](https://github.com/kubernetes/kubernetes/blob/{{page.githubbranch}}/docs/design/namespaces.md) are retrieved from the
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[Downward API](/docs/user-guide/downward-api). Next, `USER_VAR` is the name of
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an environment variable set in the [pod
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definition](/docs/user-guide/environment-guide/show-rc.yaml). Then, the dynamic Kubernetes environment
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variables are scanned and printed. These are used to find the backend
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service, named `backend-srv`. Finally, the frontend pod queries the
85+
backend service and prints the information returned. Again the backend
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pod returns its own pod name and namespace.
87+
88+
Try running the `curl` command a few times, and notice what
89+
changes. Ex: `watch -n 1 curl -s <ip>` Firstly, the frontend service
90+
is directing your request to different frontend pods each time. The
91+
frontend pods are always contacting the backend through the backend
92+
service. This results in a different backend pod servicing each
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request as well.
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## Cleanup
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```shell
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kubectl delete rc,service -l type=show-type
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kubectl delete rc,service -l type=backend-type
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```

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