guestbook-go/

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Published: Nov 19, 2014 License: Apache-2.0

README

GuestBook example

This example shows how to build a simple multi-tier web application using Kubernetes and Docker.

The example combines a web frontend, a redis master for storage and a replicated set of redis slaves.

Step Zero: Prerequisites

This example assumes that you have forked the repository and turned up a Kubernetes cluster:

$ cd kubernetes
$ hack/dev-build-and-up.sh

Step One: Turn up the redis master.

Use the file examples/guestbook-go/redis-master-pod.json which describes a single pod running a redis key-value server in a container.

Create the redis pod in your Kubernetes cluster using the kubecfg CLI:

$ cluster/kubecfg.sh -c examples/guestbook-go/redis-master-pod.json create pods

Once that's up you can list the pods in the cluster, to verify that the master is running:

$ cluster/kubecfg.sh list pods

You'll see a single redis master pod. It will also display the machine that the pod is running on once it gets placed (may take up to thirty seconds).

  ID                Image(s)            Host                                          Labels                 Status
----------          ----------          ----------                                    ----------             ----------
redis-master-pod    gurpartap/redis     kubernetes-minion-3.c.briandpe-api.internal   name=redis,role=master      Running

If you ssh to that machine, you can run docker ps to see the actual pod:

$ gcutil ssh --zone us-central1-b kubernetes-minion-3
$ sudo docker ps

me@kubernetes-minion-3:~$ sudo docker ps
CONTAINER ID  IMAGE                   COMMAND              CREATED         STATUS
e443647cd064  gurpartap/redis:latest  redis-server /etc/r  22 minutes ago  Up 22 minutes

(Note that initial docker pull may take a few minutes, depending on network conditions.)

Step Two: Turn up the 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. Services find the containers to load balance based on pod labels.

The pod that you created in Step One has the label name=redis and role=master. The selector field of the service determines which pods will receive the traffic sent to the service. Use the file examples/guestbook-go/redis-master-service.json

To create the service with the kubecfg cli:

$ cluster/kubecfg.sh -c examples/guestbook-go/redis-master-service.json create services
ID                     Labels              Selector                 Port
----------             ----------          ----------               ----------
redis-master                               name=redis,role=master   6379

This will cause all pods to see the redis master apparently running on localhost:6379.

Once created, the service proxy on each minion is configured to set up a proxy on the specified port (in this case port 6379).

Step Three: Turn up the replicated slave pods.

Although the redis master is a single pod, the redis read slaves are a 'replicated' pod. In Kubernetes, a replication controller is responsible for managing multiple instances of a replicated pod.

Use the file examples/guestbook-go/redis-slave-controller.json

to create the replication controller by running:

$ cluster/kubecfg.sh -c examples/guestbook-go/redis-slave-controller.json create replicationControllers
  ID                    Image(s)         Selector               Replicas
----------              ----------       ----------             ----------
redis-slave-controller  gurpartap/redis  name=redis,role=slave  2

The redis slave configures itself by looking for the Kubernetes service environment variables in the container environment. In particular, the redis slave is started with the following command:

redis-server --slaveof $SERVICE_HOST $REDIS_MASTER_SERVICE_PORT

Once that's up you can list the pods in the cluster, to verify that the master and slaves are running:

$ cluster/kubecfg.sh list pods
  ID              Image(s)         Host                                         Labels                                                         Status
----------        ----------       ----------                                   ----------                                                     ----------
redis-master-pod  gurpartap/redis  kubernetes-minion-3.c.briandpe-api.internal  name=redis,role=master                                              Running
4d65822107fcfd52  gurpartap/redis  kubernetes-minion-3.c.briandpe-api.internal  name=redis,role=slave,replicationController=redis-slave-controller  Running
78629a0f5f3f164f  gurpartap/redis  kubernetes-minion-4.c.briandpe-api.internal  name=redis,role=slave,replicationController=redis-slave-controller  Running

You will see a single redis master pod 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 slave service provides transparent load balancing to clients. The service specification for the slaves is in examples/guestbook-go/redis-slave-service.json

This time the selector for the service is name=redis,role=slave, because that identifies the pods running redis slaves. It may also be helpful to set labels on your service itself--as we've done here--to make it easy to locate them with the kubecfg -l "label=value" list services command.

Now that you have created the service specification, create it in your cluster with the kubecfg CLI:

$ cluster/kubecfg.sh -c examples/guestbook-go/redis-slave-service.json create services
  ID         Labels            Selector               Port
----------   ----------        ----------             ----------
redis-slave  name=redis-slave  name=redis,role=slave  6379

Step Five: Create the guestbook pod.

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. It exposes a simple JSON interface, and serves a jQuery-Ajax based UX. Like the redis read slaves it is a replicated service instantiated by a replication controller.

The pod is described in the file examples/guestbook-go/guestbook-controller.json:

Using this file, you can turn up your guestbook with:

$ cluster/kubecfg.sh -c examples/guestbook-go/guestbook-controller.json create replicationControllers
  ID                  Image(s)         Selector       Replicas
----------            ----------       ----------     ----------
guestbook-controller  gurpartap/redis  name=guestbook  3

Once that's up (it may take ten to thirty seconds to create the pods) you can list the pods in the cluster, to verify that the master, slaves and guestbook frontends are running:

$ cluster/kubecfg.sh list pods
  ID              Image(s)              Host                                         Labels                                                              Status
----------        ----------            ----------                                   ----------                                                          ----------
redis-master-pod  gurpartap/redis       kubernetes-minion-3.c.briandpe-api.internal  name=redis,role=master                                              Running
4d65822107fcfd52  gurpartap/redis       kubernetes-minion-3.c.briandpe-api.internal  name=redis,role=slave,replicationController=redis-slave-controller  Running
380704bb7b4d7c03  kubernetes/guestbook  kubernetes-minion-3.c.briandpe-api.internal  name=guestbook,replicationController=guestbook-controller           Running
55104dc76695721d  kubernetes/guestbook  kubernetes-minion-2.c.briandpe-api.internal  name=guestbook,replicationController=guestbook-controller           Running
365a858149c6e2d1  kubernetes/guestbook  kubernetes-minion-1.c.briandpe-api.internal  name=guestbook,replicationController=guestbook-controller           Running
78629a0f5f3f164f  gurpartap/redis       kubernetes-minion-4.c.briandpe-api.internal  name=redis,role=slave,replicationController=redis-slave-controller  Running

You will see a single redis master pod, two redis slaves, and three guestbook pods.

To play with the service itself, find the name of a guestbook, grab the external IP of that host from the Google Cloud Console or the gcutil tool, and visit http://<host-ip>:3000.

$ gcutil listinstances

You may need to open the firewall for port 3000 using the console or the gcutil tool. The following command will allow traffic from any source to instances tagged kubernetes-minion:

$ gcutil addfirewall --allowed=tcp:3000 --target_tags=kubernetes-minion kubernetes-minion-3000

If you are running Kubernetes locally, you can just visit http://localhost:3000 For details about limiting traffic to specific sources, see the gcutil documentation

Step Six: Cleanup

To turn down a Kubernetes cluster:

$ cluster/kube-down.sh

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