c2a3e4e811
This example shows a simple two tier setup in Kubernetes, and simply prints the environment information that each pod sees. Querying the service multiple times will show services at work load balancing requests.
93 lines
3.3 KiB
Markdown
93 lines
3.3 KiB
Markdown
Environment Guide Example
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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/container-environment.md).
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Prerequisites
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-------------
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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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-----------------------------------
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The code for the containers is under
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[containers/](containers)
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Get everything running
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----------------------
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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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Query the service
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-----------------
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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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```
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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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Kubenertes 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](/docs/design/namespaces.md) are retreived from the
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[Downward API](/docs/downward_api.md). Next, `USER_VAR` is the name of
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an environment variable set in the [pod
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definition](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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-------
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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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