README
¶
PLEASE NOTE: This document applies to the HEAD of the source tree
If you are using a released version of Kubernetes, you should refer to the docs that go with that version.
The latest 1.0.x release of this document can be found [here](http://releases.k8s.io/release-1.0/examples/guestbook-go/README.md).Documentation for other releases can be found at releases.k8s.io.
Guestbook Example
This example shows how to build a simple multi-tier web application using Kubernetes and Docker. The application consists of a web front-end, Redis master for storage, and replicated set of Redis slaves, all for which we will create Kubernetes replication controllers, pods, and services.
If you are running a cluster in Google Container Engine (GKE), instead see the Guestbook Example for Google Container Engine.
Table of Contents
- Step Zero: Prerequisites
- Step One: Create the Redis master pod
- Step Two: Create the Redis master service
- Step Three: Create the Redis slave pods
- Step Four: Create the Redis slave service
- Step Five: Create the guestbook pods
- Step Six: Create the guestbook service
- Step Seven: View the guestbook
- Step Eight: Cleanup
Step Zero: Prerequisites
This example assumes that you have a working cluster. See the Getting Started Guides for details about creating a cluster.
Tip: View all the kubectl commands, including their options and descriptions in the kubectl CLI reference.
Step One: Create the Redis master pod
Use the examples/guestbook-go/redis-master-controller.json file to create a replication controller and Redis master pod. The pod runs a Redis key-value server in a container. Using a replication controller is the preferred way to launch long-running pods, even for 1 replica, so that the pod benefits from the self-healing mechanism in Kubernetes (keeps the pods alive).
1. Use the redis-master-controller.json file to create the Redis master replication controller in your Kubernetes cluster by running the kubectl create -f filename command:
```console
$ kubectl create -f examples/guestbook-go/redis-master-controller.json
replicationcontrollers/redis-master
```
2. To verify that the redis-master-controller is up, list all the replication controllers in the cluster with the kubectl get rc command:
```console
$ kubectl get rc
CONTROLLER CONTAINER(S) IMAGE(S) SELECTOR REPLICAS
redis-master redis-master gurpartap/redis app=redis,role=master 1
...
```
Result: The replication controller then creates the single Redis master pod.
3. To verify that the redis-master pod is running, list all the pods in cluster with the kubectl get pods command:
```console
$ kubectl get pods
NAME READY STATUS RESTARTS AGE
redis-master-xx4uv 1/1 Running 0 1m
...
```
Result: You'll see a single Redis master pod and the machine where the pod is running after the pod gets placed (may take up to thirty seconds).
4. To verify what containers are running in the redis-master pod, you can SSH to that machine with gcloud comput ssh --zone zone_name host_name and then run docker ps:
```console
me@workstation$ gcloud compute ssh --zone us-central1-b kubernetes-minion-bz1p
me@kubernetes-minion-3:~$ sudo docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS
d5c458dabe50 gurpartap/redis:latest "/usr/local/bin/redi 5 minutes ago Up 5 minutes
```
Note: The initial `docker pull` can take a few minutes, depending on network conditions.
Step Two: Create the Redis master service
A Kubernetes 'service' is a named load balancer that proxies traffic to one or more containers. The services in a Kubernetes cluster are discoverable inside other containers via environment variables or DNS.
Services find the containers to load balance based on pod labels. The pod that you created in Step One has the label app=redis and role=master. The selector field of the service determines which pods will receive the traffic sent to the service.
1. Use the redis-master-service.json file to create the service in your Kubernetes cluster by running the kubectl create -f filename command:
```console
$ kubectl create -f examples/guestbook-go/redis-master-service.json
services/redis-master
```
2. To verify that the redis-master service is up, list all the services in the cluster with the kubectl get services command:
```console
$ kubectl get services
NAME CLUSTER_IP EXTERNAL_IP PORT(S) SELECTOR AGE
redis-master 10.0.136.3 <none> 6379/TCP app=redis,role=master 1h
...
```
Result: All new pods will see the `redis-master` service running on the host (`$REDIS_MASTER_SERVICE_HOST` environment variable) at port 6379, or running on `redis-master:6379`. After the service is created, the service proxy on each node is configured to set up a proxy on the specified port (in our example, that's port 6379).
Step Three: Create the Redis slave pods
The Redis master we created earlier is a single pod (REPLICAS = 1), while the Redis read slaves we are creating here are 'replicated' pods. In Kubernetes, a replication controller is responsible for managing the multiple instances of a replicated pod.
1. Use the file redis-slave-controller.json to create the replication controller by running the kubectl create -f filename command:
```console
$ kubectl create -f examples/guestbook-go/redis-slave-controller.json
replicationcontrollers/redis-slave
```
2. To verify that the guestbook replication controller is running, run the kubectl get rc command:
```console
$ kubectl get rc
CONTROLLER CONTAINER(S) IMAGE(S) SELECTOR REPLICAS
redis-master redis-master gurpartap/redis app=redis,role=master 1
redis-slave redis-slave gurpartap/redis app=redis,role=slave 2
...
```
Result: The replication controller creates and configures the Redis slave pods through the redis-master service (name:port pair, in our example that's `redis-master:6379`).
Example:
The Redis slaves get started by the replication controller with the following command:
```console
redis-server --slaveof redis-master 6379
```
3. To verify that the Redis master and slaves pods are running, run the kubectl get pods command:
```console
$ kubectl get pods
NAME READY STATUS RESTARTS AGE
redis-master-xx4uv 1/1 Running 0 18m
redis-slave-b6wj4 1/1 Running 0 1m
redis-slave-iai40 1/1 Running 0 1m
...
```
Result: You see the single Redis master and two Redis slave pods.
Step Four: Create the Redis slave service
Just like the master, we want to have a service to proxy connections to the read slaves. In this case, in addition to discovery, the Redis slave service provides transparent load balancing to clients.
1. Use the redis-slave-service.json file to create the Redis slave service by running the kubectl create -f filename command:
```console
$ kubectl create -f examples/guestbook-go/redis-slave-service.json
services/redis-slave
```
2. To verify that the redis-slave service is up, list all the services in the cluster with the kubectl get services command:
```console
$ kubectl get services
NAME CLUSTER_IP EXTERNAL_IP PORT(S) SELECTOR AGE
redis-master 10.0.136.3 <none> 6379/TCP app=redis,role=master 1h
redis-slave 10.0.21.92 <none> 6379/TCP app-redis,role=slave 1h
...
```
Result: The service is created with labels `app=redis` and `role=slave` to identify that the pods are running the Redis slaves.
Tip: It is helpful to set labels on your services themselves--as we've done here--to make it easy to locate them later.
Step Five: Create the guestbook pods
This is a simple Go net/http (negroni based) server that is configured to talk to either the slave or master services depending on whether the request is a read or a write. The pods we are creating expose a simple JSON interface and serves a jQuery-Ajax based UI. Like the Redis read slaves, these pods are also managed by a replication controller.
1. Use the guestbook-controller.json file to create the guestbook replication controller by running the kubectl create -f filename command:
```console
$ kubectl create -f examples/guestbook-go/guestbook-controller.json
replicationcontrollers/guestbook
```
2. To verify that the guestbook replication controller is running, run the kubectl get rc command:
```
$ kubectl get rc
CONTROLLER CONTAINER(S) IMAGE(S) SELECTOR REPLICAS
guestbook guestbook kubernetes/guestbook:v2 app=guestbook 3
redis-master redis-master gurpartap/redis app=redis,role=master 1
redis-slave redis-slave gurpartap/redis app=redis,role=slave 2
...
```
3. To verify that the guestbook pods are running (it might take up to thirty seconds to create the pods), list all the pods in cluster with the kubectl get pods command:
```console
$ kubectl get pods
NAME READY STATUS RESTARTS AGE
guestbook-3crgn 1/1 Running 0 2m
guestbook-gv7i6 1/1 Running 0 2m
guestbook-x405a 1/1 Running 0 2m
redis-master-xx4uv 1/1 Running 0 23m
redis-slave-b6wj4 1/1 Running 0 6m
redis-slave-iai40 1/1 Running 0 6m
...
```
Result: You see a single Redis master, two Redis slaves, and three guestbook pods.
Step Six: Create the guestbook service
Just like the others, we create a service to group the guestbook pods but this time, to make the guestbook front-end externally visible, we specify "type": "LoadBalancer".
1. Use the guestbook-service.json file to create the guestbook service by running the kubectl create -f filename command:
```console
$ kubectl create -f examples/guestbook-go/guestbook-service.json
```
2. To verify that the guestbook service is up, list all the services in the cluster with the kubectl get services command:
```
$ kubectl get services
NAME CLUSTER_IP EXTERNAL_IP PORT(S) SELECTOR AGE
guestbook 10.0.217.218 146.148.81.8 3000/TCP app=guestbook 1h
redis-master 10.0.136.3 <none> 6379/TCP app=redis,role=master 1h
redis-slave 10.0.21.92 <none> 6379/TCP app-redis,role=slave 1h
...
```
Result: The service is created with label `app=guestbook`.
Step Seven: View the guestbook
You can now play with the guestbook that you just created by opening it in a browser (it might take a few moments for the guestbook to come up).
-
Local Host: If you are running Kubernetes locally, to view the guestbook, navigate to
http://localhost:3000in your browser. -
Remote Host:
-
To view the guestbook on a remote host, locate the external IP of the load balancer in the IP column of the
kubectl get servicesoutput. In our example, the internal IP address is10.0.217.218and the external IP address is146.148.81.8(Note: you might need to scroll to see the IP column). -
Append port
3000to the IP address (for examplehttp://146.148.81.8:3000), and then navigate to that address in your browser.
Result: The guestbook displays in your browser:
Further Reading: If you're using Google Compute Engine, see the details about limiting traffic to specific sources at Google Compute Engine firewall documentation.
-
Step Eight: Cleanup
After you're done playing with the guestbook, you can cleanup by deleting the guestbook service and removing the associated resources that were created, including load balancers, forwarding rules, target pools, and Kubernetes replication controllers and services.
Delete all the resources by running the following kubectl delete -f filename command:
$ kubectl delete -f examples/guestbook-go
guestbook-controller
guestbook
redid-master-controller
redis-master
redis-slave-controller
redis-slave
Tip: To turn down your Kubernetes cluster, follow the corresponding instructions in the version of the Getting Started Guides that you previously used to create your cluster.
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