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 kubectl CLI:
$ cluster/kubectl.sh create -f examples/guestbook-go/redis-master-pod.json
Once that's up you can list the pods in the cluster, to verify that the master is running:
$ cluster/kubectl.sh 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).
ID IMAGE(S) HOST LABELS STATUS
redis-master-pod gurpartap/redis kubernetes-minion-3.c.thockin-dev.internal/86.75.30.9 name=redis,role=master Waiting
If you ssh to that machine, you can run docker ps to see the actual pod:
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
e443647cd064 gurpartap/redis:latest redis-server /etc/r 2 minutes ago Up 2 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 kubectl cli:
$ cluster/kubectl.sh create -f examples/guestbook-go/redis-master-service.json
$ cluster/kubectl.sh get services
ID LABELS SELECTOR PORT
redis-master name=redis,role=master 6379
This will cause all new pods to see the redis master apparently running on $REDIS_MASTER_SERVICE_HOST at port 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/kubectl.sh create -f examples/guestbook-go/redis-slave-controller.json
$ cluster/kubectl.sh get 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 $REDIS_MASTER_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/kubectl.sh get pods
ID IMAGE(S) HOST LABELS STATUS
redis-master-pod gurpartap/redis kubernetes-minion-1.c.thockin-dev.internal/86.75.30.9 name=redis,role=master Running
1472fd26-54d6-11e4-90fd-42010af00690 gurpartap/redis kubernetes-minion-4.c.thockin-dev.internal/12.34.56.78 name=redis,replicationController=redis-slave-controller,role=slave Running
1473363e-54d6-11e4-90fd-42010af00690 gurpartap/redis kubernetes-minion-3.c.thockin-dev.internal/9.3.19.76 name=redis,replicationController=redis-slave-controller,role=slave 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 later.
Now that you have created the service specification, create it in your cluster with the kubectl CLI:
$ cluster/kubectl.sh create -f examples/guestbook-go/redis-slave-service.json
$ cluster/kubectl.sh get services
ID LABELS SELECTOR PORT
redis-master name=redis,role=master 6379
redis-slave name=redis,role=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/kubectl.sh create -f examples/guestbook-go/guestbook-controller.json
$ cluster/kubectl.sh get replicationControllers
ID IMAGE(S) SELECTOR REPLICAS
redis-slave-controller gurpartap/redis name=redis,role=slave 2
guestbook-controller kubernetes/guestbook 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/kubectl.sh get pods
ID IMAGE(S) HOST LABELS STATUS
redis-master-pod gurpartap/redis kubernetes-minion-1.c.thockin-dev.internal/86.75.30.9 name=redis,role=master Running
1472fd26-54d6-11e4-90fd-42010af00690 gurpartap/redis kubernetes-minion-4.c.thockin-dev.internal/12.34.56.78 name=redis,replicationController=redis-slave-controller,role=slave Running
1473363e-54d6-11e4-90fd-42010af00690 gurpartap/redis kubernetes-minion-3.c.thockin-dev.internal/9.3.19.76 name=redis,replicationController=redis-slave-controller,role=slave Running
fc58aa01-54d6-11e4-90fd-42010af00690 kubernetes/guestbook kubernetes-minion-1.c.thockin-dev.internal/1.18.19.78 name=guestbook,replicationController=guestbook-controller Running
fc592fbb-54d6-11e4-90fd-42010af00690 kubernetes/guestbook kubernetes-minion-1.c.thockin-dev.internal/12.9.20.9 name=guestbook,replicationController=guestbook-controller Running
fc59569e-54d6-11e4-90fd-42010af00690 kubernetes/guestbook kubernetes-minion-2.c.thockin-dev.internal/1.11.20.13 name=guestbook,replicationController=guestbook-controller Running
You will see a single redis master pod, two redis slaves, and three guestbook pods.
Step Six: Create the guestbook service.
Just like the others, you want a service to group your guestbook pods. The service specification for the guestbook is in examples/guestbook-go/guestbook-service.json. There's a twist this time - because we want it to be externally visible, we set the createExternalLoadBalancer flag on the service.
$ cluster/kubectl.sh create -f examples/guestbook-go/guestbook-service.json
$ cluster/kubectl.sh get services
ID LABELS SELECTOR IP PORT
redis-master name=redis,role=master 10.0.0.1 6379
redis-slave name=redis,role=slave name=redis,role=slave 10.0.0.2 6379
guestbook name=guestbook 10.0.0.3 3000
To play with the service itself, find the external IP of the load balancer from the Google Cloud Console or the gcloud tool, and visit http://<ip>:3000.
$ gcloud compute forwarding-rules describe --region=us-central1 guestbook
IPAddress: 11.22.33.44
IPProtocol: TCP
creationTimestamp: '2014-11-24T16:08:15.327-08:00'
id: '17594840560849468061'
kind: compute#forwardingRule
name: guestbook
portRange: 1-65535
region: https://www.googleapis.com/compute/v1/projects/jbeda-prod/regions/us-central1
selfLink: https://www.googleapis.com/compute/v1/projects/jbeda-prod/regions/us-central1/forwardingRules/guestbook
target: https://www.googleapis.com/compute/v1/projects/jbeda-prod/regions/us-central1/targetPools/guestbook
You may need to open the firewall for port 3000 using the console or the gcloud tool. The following command will allow traffic from any source to instances tagged kubernetes-minion:
$ gcloud compute firewall-rules create --allow=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 GCE firewall documentation.
Step Seven: Cleanup
To turn down a Kubernetes cluster:
$ cluster/kube-down.sh
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