## 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](https://github.com/GoogleCloudPlatform/kubernetes#contents):

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

### Step One: Turn up the redis master

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

```js
{
  "id": "redis-master",
  "kind": "Pod",
  "apiVersion": "v1beta1",
  "desiredState": {
    "manifest": {
      "version": "v1beta1",
      "id": "redis-master",
      "containers": [{
        "name": "master",
        "image": "dockerfile/redis",
        "cpu": 100,
        "ports": [{
          "containerPort": 6379,
          "hostPort": 6379
        }]
      }]
    }
  },
  "labels": {
    "name": "redis-master"
  }
}
```

Create the redis pod in your Kubernetes cluster by running:

```shell
$ cluster/kubecfg.sh -c examples/guestbook/redis-master.json create pods
```

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

```shell
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        dockerfile/redis    kubernetes-minion-3.c.briandpe-api.internal   name=redis-master      Running
```

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

```shell
me@workstation$ gcloud compute ssh --zone us-central1-b kubernetes-minion-3

me@kubernetes-minion-3:~$ sudo docker ps
CONTAINER ID  IMAGE                     COMMAND               CREATED         STATUS        PORTS     NAMES
e3eed3e5e6d1  dockerfile/redis:latest   redis-server /etc/re  8 minutes ago   Up 8 minutes            k8s_master.9c0a9146_redis-master.etcd_6296f4bd-70fa-11e4-8469-0800279696e1_45331ebc
```

(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-master`. The selector field of the service determines which pods will receive the traffic sent to the service. Use the file `examples/guestbook/redis-master-service.json`:

```js
{
  "id": "redis-master",
  "kind": "Service",
  "apiVersion": "v1beta1",
  "port": 6379,
  "containerPort": 6379,
  "selector": {
    "name": "redis-master"
  },
  "labels": {
    "name": "redis-master"
  }
}
```

to create the service by running:

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

This will cause all pods to see the redis master apparently running on <ip>: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/redis-slave-controller.json`:

```js
{
  "id": "redisSlaveController",
  "kind": "ReplicationController",
  "apiVersion": "v1beta1",
  "desiredState": {
    "replicas": 2,
    "replicaSelector": {"name": "redisslave"},
    "podTemplate": {
      "desiredState": {
         "manifest": {
           "version": "v1beta1",
           "id": "redisSlaveController",
           "containers": [{
             "name": "slave",
             "image": "brendanburns/redis-slave",
             "cpu": 200,
             "ports": [{"containerPort": 6379, "hostPort": 6380}]
           }]
         }
       },
       "labels": {
         "name": "redisslave",
         "uses": "redis-master",
       }
      }},
  "labels": {"name": "redisslave"}
}
```

to create the replication controller by running:

```shell
$ cluster/kubecfg.sh -c examples/guestbook/redis-slave-controller.json create replicationControllers
ID                     Image(s)                   Selector            Replicas
----------             ----------                 ----------          ----------
redisSlaveController   brendanburns/redis-slave   name=redisslave     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:

```shell
redis-server --slaveof ${REDIS_MASTER_SERVICE_HOST:-$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:

```shell
$ cluster/kubecfg.sh list pods
ID                                      Image(s)                   Host                                          Labels                                                                          Status
----------                              ----------                 ----------                                    ----------                                                                      ----------
redis-master                            dockerfile/redis           kubernetes-minion-3.c.briandpe-api.internal   name=redis-master                                                               Running
e4469b52-70e7-11e4-9154-0800279696e1    brendanburns/redis-slave   kubernetes-minion-3.c.briandpe-api.internal   name=redisslave,replicationController=redisSlaveController,uses=redis-master    Running
e446dfc0-70e7-11e4-9154-0800279696e1    brendanburns/redis-slave   kubernetes-minion-4.c.briandpe-api.internal   name=redisslave,replicationController=redisSlaveController,uses=redis-master    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/redis-slave-service.json`:

```js
{
  "id": "redisslave",
  "kind": "Service",
  "apiVersion": "v1beta1",
  "port": 6379,
  "containerPort": 6379,
  "labels": {
    "name": "redisslave"
  },
  "selector": {
    "name": "redisslave"
  }
}
```

This time the selector for the service is `name=redisslave`, 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 `cluster/kubecfg.sh -l "label=value" list services` command.

Now that you have created the service specification, create it in your cluster by running:

```shell
$ cluster/kubecfg.sh -c examples/guestbook/redis-slave-service.json create services
ID                  Labels              Selector            Port
----------          ----------          ----------          ----------
redisslave          name=redisslave     name=redisslave     6379
```

### Step Five: Create the frontend pod

This is a simple PHP 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 AJAX interface, and serves an angular-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/frontend-controller.json`:

```js
{
  "id": "frontendController",
  "kind": "ReplicationController",
  "apiVersion": "v1beta1",
  "desiredState": {
    "replicas": 3,
    "replicaSelector": {"name": "frontend"},
    "podTemplate": {
      "desiredState": {
         "manifest": {
           "version": "v1beta1",
           "id": "frontendController",
           "containers": [{
             "name": "php-redis",
             "image": "brendanburns/php-redis",
             "cpu": 100,
             "memory": 50000000,
             "ports": [{"containerPort": 80, "hostPort": 8000}]
           }]
         }
       },
       "labels": {
         "name": "frontend",
         "uses": "redisslave,redis-master"
       }
      }},
  "labels": {"name": "frontend"}
}
```

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

```shell
$ cluster/kubecfg.sh -c examples/guestbook/frontend-controller.json create replicationControllers
ID                   Image(s)                 Selector            Replicas
----------           ----------               ----------          ----------
frontendController   brendanburns/php-redis   name=frontend       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 frontends are running:

```shell
$ cluster/kubecfg.sh list pods
ID                                      Image(s)                   Host                                          Labels                                                                                      Status
----------                              ----------                 ----------                                    ----------                                                                                  ----------
redis-master                            dockerfile/redis           kubernetes-minion-3.c.briandpe-api.internal   name=redis-master                                                                           Running
e4469b52-70e7-11e4-9154-0800279696e1    brendanburns/redis-slave   kubernetes-minion-3.c.briandpe-api.internal   name=redisslave,replicationController=redisSlaveController,uses=redis-master                Running
e446dfc0-70e7-11e4-9154-0800279696e1    brendanburns/redis-slave   kubernetes-minion-4.c.briandpe-api.internal   name=redisslave,replicationController=redisSlaveController,uses=redis-master                Running
6b584847-70ee-11e4-9154-0800279696e1    brendanburns/php-redis     kubernetes-minion-3.c.briandpe-api.internal   name=frontend,replicationController=frontendController,uses=redisslave,redis-master         Running
6b59e6d5-70ee-11e4-9154-0800279696e1    brendanburns/php-redis     kubernetes-minion-2.c.briandpe-api.internal   name=frontend,replicationController=frontendController,uses=redisslave,redis-master         Running
6b57a25d-70ee-11e4-9154-0800279696e1    brendanburns/php-redis     kubernetes-minion-1.c.briandpe-api.internal   name=frontend,replicationController=frontendController,uses=redisslave,redis-master         Running
```

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

The code for the PHP service looks like this:

```php
<?

set_include_path('.:/usr/share/php:/usr/share/pear:/vendor/predis');

error_reporting(E_ALL);
ini_set('display_errors', 1);

require 'predis/autoload.php';

if (isset($_GET['cmd']) === true) {
  header('Content-Type: application/json');
  if ($_GET['cmd'] == 'set') {
    $client = new Predis\Client([
      'scheme' => 'tcp',
      'host'   => getenv('REDIS_MASTER_SERVICE_HOST') ?: getenv('SERVICE_HOST'),
      'port'   => getenv('REDIS_MASTER_SERVICE_PORT'),
    ]);
    $client->set($_GET['key'], $_GET['value']);
    print('{"message": "Updated"}');
  } else {
    $read_port = getenv('REDIS_MASTER_SERVICE_PORT');

    if (isset($_ENV['REDISSLAVE_SERVICE_PORT'])) {
      $read_port = getenv('REDISSLAVE_SERVICE_PORT');
    }
    $client = new Predis\Client([
      'scheme' => 'tcp',
      'host'   => getenv('REDIS_MASTER_SERVICE_HOST') ?: getenv('SERVICE_HOST'),
      'port'   => $read_port,
    ]);

    $value = $client->get($_GET['key']);
    print('{"data": "' . $value . '"}');
  }
} else {
  phpinfo();
} ?>
```

To play with the service itself, find the name of a frontend, grab the external IP of that host from the [Google Cloud Console][cloud-console] or the `gcloud` tool, and visit `http://<host-ip>:8000`.

```shell
$ gcloud compute instances list
```

You may need to open the firewall for port 8000 using the [console][cloud-console] or the `gcloud` tool. The following command will allow traffic from any source to instances tagged `kubernetes-minion`:

```shell
$ gcloud compute firewall-rules create --allow=tcp:8000 --target-tags=kubernetes-minion kubernetes-minion-8000
```

If you are running Kubernetes locally, you can just visit http://localhost:8000.
For details about limiting traffic to specific sources, see the [GCE firewall documentation][gce-firewall-docs].

[cloud-console]: https://console.developer.google.com
[gce-firewall-docs]: https://cloud.google.com/compute/docs/networking#firewalls

### Step Six: Cleanup

To turn down a Kubernetes cluster:

```shell
$ cluster/kube-down.sh
```
