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…/GCE setup, and added details around redis master and convenient cleanup utility script snippet.
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115 changes: 75 additions & 40 deletions examples/guestbook/README.md
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## GuestBook example

This example shows how to build a simple multi-tier web application using Kubernetes and Docker.
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.
The example consists of:
- A web frontend
- A redis master (for storage and a replicated set of redis slaves)

The web front end interacts with the redis master via javascript redis API calls.

### Step Zero: Prerequisites

This example assumes that you have a basic understanding of kubernetes services and that you have forked the repository and [turned up a Kubernetes cluster](https://github.com/GoogleCloudPlatform/kubernetes#contents):
This example requires a kubernetes cluster.

```shell
$ cd kubernetes
$ hack/dev-build-and-up.sh
```
See the companion [Setup Kubernetes](https://github.com/GoogleCloudPlatform/kubernetes/blob/master/examples/guestbook/SETUP.md) for some quick notes on how to get started.

*If* you are running from source, replace commands such as "kubectl" below with calls to cluster/kubectl.sh.

### Step One: Turn up the redis master
### Step One: Fire 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:
Note: This redis-master is *not* highly available. Making it highly available would be a very interesting, but intricate exersize - redis doesn't actually support multi-master deployments at the time of this writing, so high availability would be a somewhat tricky thing implement, and might involve periodic serialization to disk, and so on.

Use (or just create) 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",
"apiVersion": "v1beta1",
"desiredState": {
"manifest": {
"version": "v1beta1",
Expand All @@ -31,35 +37,35 @@ Use the file `examples/guestbook/redis-master.json` which describes a single pod
"image": "dockerfile/redis",
"cpu": 100,
"ports": [{
"containerPort": 6379,
"hostPort": 6379
"containerPort": 6379, # containerPort: Where traffic to redis ultimately is routed to.
}]
}]
}
},
"labels": {
"name": "redis-master"
"name": "redis-master" # This label needed for when we start our redis-master service.
}
}
```

Create the redis pod in your Kubernetes cluster by running:
Now, create the redis pod in your Kubernetes cluster by running:

```shell
$ cluster/kubectl.sh create -f examples/guestbook/redis-master.json
kubectl create -f examples/guestbook/redis-master.json
```

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

```shell
cluster/kubectl.sh get pods
kubectl get 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):
You'll see all kubernetes components, most importantly the 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):

```
```shell
NAME IMAGE(S) HOST LABELS STATUS
redis-master dockerfile/redis kubernetes-minion-2.c.myproject.internal/130.211.156.189 name=redis-master Running

```

If you ssh to that machine, you can run `docker ps` to see the actual pod:
Expand All @@ -72,13 +78,18 @@ CONTAINER ID IMAGE COMMAND CREATED S
e3eed3e5e6d1 dockerfile/redis:latest "redis-server /etc/re 2 minutes ago Up 2 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. During this time, the `get pods` command will return `Pending` because the container has not yet started )
(Note that initial `docker pull` may take a few minutes, depending on network conditions. You can monitor the status of this by running `journalctl -f -u docker` to check when the image is being downloaded. Of course, you can also run `journalctl -f -u kubelet` to see what state the kubelet is in as well during this time.
### Step Two: Turn up the master service
### Step Two: Fire up the master service
A Kubernetes 'service' is a named load balancer that proxies traffic to *one or more* containers. This is done using the *labels* metadata which we defined in the redis-master pod above. As mentioned, in redis there is only one master, but we nevertheless still want to create a service for it. Why? Because it gives us a deterministic way to route to the single master using an elastic IP.
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. These environment variables are typically referenced in application code, shell scripts, or other places where one node needs to talk to another in a distributed system. You should catch up on [kubernetes services](https://github.com/GoogleCloudPlatform/kubernetes/blob/master/docs/services.md) before proceeding.
The services in a Kubernetes cluster are discoverable inside other containers via environment variables.
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`:
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, and the port and containerPort information defines what port the service proxy will run at.
Use the file `examples/guestbook/redis-master-service.json`:
```js
{
Expand All @@ -99,7 +110,7 @@ The pod that you created in Step One has the label `name=redis-master`. The sele
to create the service by running:
```shell
$ cluster/kubectl.sh create -f examples/guestbook/redis-master-service.json
$ kubectl create -f examples/guestbook/redis-master-service.json
redis-master
$ cluster/kubectl.sh get services
Expand All @@ -110,14 +121,17 @@ redis-master name=redis-master name=redis-master
```
This will cause all pods to see the redis master apparently running on <ip>:6379.
This will cause all pods to see the redis master apparently running on <ip>:6379. The traffic flow from slaves to masters can be described in two steps, like so.
- A *redis slave* will connect to "port" on the *redis master service*
- Traffic will be forwarded from the service "port" (on the service node) to the *containerPort* on the pod which (a node the service listens to).
Once created, the service proxy on each minion is configured to set up a proxy on the specified port (in this case port 6379).
Thus, 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.
### Step Three: Fire 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. The replicationController will automatically launch new Pods if the number of replicas falls (this is quite easy - and fun - to test, just kill the docker processes for your pods at will and watch them come back online on a new node shortly thereafter).
Use the file `examples/guestbook/redis-slave-controller.json`:
Use the file `examples/guestbook/redis-slave-controller.json`, which looks like this:
```js
{
Expand All @@ -142,7 +156,7 @@ Use the file `examples/guestbook/redis-slave-controller.json`:
},
"labels": {
"name": "redisslave",
"uses": "redis-master",
"uses": "redis-master"
}
}},
"labels": {"name": "redisslave"}
Expand All @@ -152,12 +166,12 @@ Use the file `examples/guestbook/redis-slave-controller.json`:
to create the replication controller by running:
```shell
$ cluster/kubectl.sh create -f examples/guestbook/redis-slave-controller.json
$ kubectl create -f examples/guestbook/redis-slave-controller.json
redis-slave-controller
# cluster/kubectl.sh get replicationcontrollers
NAME IMAGE(S) SELECTOR REPLICAS
redis-slave-controller brendanburns/redis-slave name=redisslave 2
# kubectl.sh get replicationcontrollers
NAME IMAGE(S) SELECTOR REPLICAS
redis-slave-controller 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:
Expand All @@ -171,7 +185,7 @@ You might be curious about where the *REDIS_MASTER_SERVICE_HOST* is coming from.
Once that's up you can list the pods in the cluster, to verify that the master and slaves are running:
```shell
$ cluster/kubectl.sh get pods
$ kubectl get pods
NAME IMAGE(S) HOST LABELS STATUS
redis-master dockerfile/redis kubernetes-minion-2.c.myproject.internal/130.211.156.189 name=redis-master Running
ee68394b-7fca-11e4-a220-42010af0a5f1 brendanburns/redis-slave kubernetes-minion-3.c.myproject.internal/130.211.179.212 name=redisslave,uses=redis-master Running
Expand All @@ -182,7 +196,9 @@ 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`:
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 web app clients.
The service specification for the slaves is in `examples/guestbook/redis-slave-service.json`:
```js
{
Expand Down Expand Up @@ -221,6 +237,8 @@ redisslave name=redisslave name=redisslave
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.
It can now leverage writes to the load balancing redis-slaves, which can be highly replicated.
The pod is described in the file `examples/guestbook/frontend-controller.json`:
```js
Expand Down Expand Up @@ -323,28 +341,45 @@ if (isset($_GET['cmd']) === true) {
} ?>
```
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`.
To play with the service itself, find the name of a frontend,
### A few Google Container Engine specifics for playing around with the services.
- In GCE, you can 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`:
In GCE, you also 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].
For GCE 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
In other environments, you can get the service IP from looking at the output of `kubectl get pods,services`, and modify your firewall using standard tools and services (firewalld, iptables, selinux) which you are already familar with.
And of course, finally, if you are running Kubernetes locally, you can just visit http://localhost:8000.
### Step Six: Cleanup
To turn down a Kubernetes cluster:
To turn down a Kubernetes cluster, if you ran this from source, you can use
```shell
$ cluster/kube-down.sh
```
If you are in a live kubernetes cluster, you can just kill the pods, using a script such as this (obviously, read through it and make sure you understand it before running it blindly, as it will kill several pods automatically for you).
```shell
### First, kill services and controllers.
kubectl stop rc examples/guestbook/redis-slave-controller.json
kubectl stop rc examples/guestbook/frontend-controller.json
kubectl delete -f examples/guestbook/redis-master-service.json
kubectl delete -f examples/guestbook/redis-slave-service.json
kubectl delete pod redis-master # This is the only pod that requires manual removal.
```
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## Getting Started

This example requires that you have forked the repository and [fired up a Kubernetes cluster](https://github.com/GoogleCloudPlatform/kubernetes#contents.

On some setups, this can be as easy as running:
```shell
$ cd kubernetes
$ hack/dev-build-and-up.sh
```

For others, there are also many other ways to set up a kubernetes cluster. For comprehensive directions on setting up, see the getting started guides [Getting Started Guides](https://github.com/GoogleCloudPlatform/kubernetes/tree/master/docs/getting-started-guides).

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