README
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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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