mirror of https://github.com/k3s-io/k3s
210 lines
13 KiB
Markdown
210 lines
13 KiB
Markdown
## GuestBook example
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This example shows how to build a simple multi-tier web application using Kubernetes and Docker. It consists of a web frontend, a redis master for storage and a replicated set of redis slaves.
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### Step Zero: Prerequisites
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This example assumes that you have forked the repository and [turned up a Kubernetes cluster](../../docs/getting-started-guides):
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```shell
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$ cd kubernetes
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$ hack/dev-build-and-up.sh
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```
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### Step One: Turn up the redis master.
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Use the file `examples/guestbook-go/redis-master-controller.json` to create a [replication controller](../../docs/replication-controller.md) which manages a single [pod](../../docs/pods.md). The pod runs a redis key-value server in a container. Using a replication controller is the preferred way to launch long-running pods, even for 1 replica, so the pod will benefit from self-healing mechanism in kubernetes.
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Create the redis master replication controller in your Kubernetes cluster using the `kubectl` CLI:
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```shell
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$ kubectl create -f examples/guestbook-go/redis-master-controller.json
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```
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Once that's up you can list the replication controllers in the cluster:
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```shell
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$ kubectl get rc
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CONTROLLER CONTAINER(S) IMAGE(S) SELECTOR REPLICAS
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redis-master-controller redis-master gurpartap/redis name=redis,role=master 1
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```
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List pods in cluster to verify the master is running. 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).
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```shell
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$ kubectl get pods
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POD IP CONTAINER(S) IMAGE(S) HOST LABELS STATUS CREATED MESSAGE
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redis-master-y06lj 10.244.3.4 kubernetes-minion-bz1p/104.154.61.231 name=redis,role=master Running 8 seconds
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redis-master gurpartap/redis Running 3 seconds
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```
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If you ssh to that machine, you can run `docker ps` to see the actual pod:
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```shell
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me@workstation$ gcloud compute ssh --zone us-central1-b kubernetes-minion-bz1p
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me@kubernetes-minion-3:~$ sudo docker ps
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CONTAINER ID IMAGE COMMAND CREATED STATUS
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d5c458dabe50 gurpartap/redis:latest "/usr/local/bin/redi 5 minutes ago Up 5 minutes
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```
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(Note that initial `docker pull` may take a few minutes, depending on network conditions.)
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### Step Two: Turn up the master service.
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A Kubernetes '[service](../../docs/services.md)' 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 or DNS. Services find the containers to load balance based on pod labels.
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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 in the `kubectl` cli:
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```shell
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$ kubectl create -f examples/guestbook-go/redis-master-service.json
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$ kubectl get services
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NAME LABELS SELECTOR IP(S) PORT(S)
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redis-master name=redis,role=master name=redis,role=master 10.0.11.173 6379/TCP
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```
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This will cause all new pods to see the redis master apparently running on $REDIS_MASTER_SERVICE_HOST at port 6379, or running on 'redis-master:6379'. Once created, the service proxy on each node is configured to set up a proxy on the specified port (in this case port 6379).
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### Step Three: Turn up the replicated slave pods.
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Although the redis master is a single pod, the redis read slaves are a 'replicated' pod. In Kubernetes, a replication controller is responsible for managing multiple instances of a replicated pod.
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Use the file `examples/guestbook-go/redis-slave-controller.json` to create the replication controller:
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```shell
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$ kubectl create -f examples/guestbook-go/redis-slave-controller.json
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$ kubectl get rc
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CONTROLLER CONTAINER(S) IMAGE(S) SELECTOR REPLICAS
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redis-master redis-master gurpartap/redis name=redis,role=master 1
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redis-slave redis-slave gurpartap/redis name=redis,role=slave 2
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```
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The redis slave configures itself by looking for the redis-master service name:port pair. In particular, the redis slave is started with the following command:
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```shell
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redis-server --slaveof redis-master 6379
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```
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Once that's up you can list the pods in the cluster, to verify that the master and slaves are running:
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```shell
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$ kubectl get pods
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POD IP CONTAINER(S) IMAGE(S) HOST LABELS STATUS CREATED MESSAGE
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redis-master-y06lj 10.244.3.4 kubernetes-minion-bz1p/104.154.61.231 name=redis,role=master Running 5 minutes
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redis-master gurpartap/redis Running 5 minutes
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redis-slave-3psic 10.244.0.4 kubernetes-minion-mluf/104.197.10.10 name=redis,role=slave Running 38 seconds
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redis-slave gurpartap/redis Running 33 seconds
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redis-slave-qtigf 10.244.2.4 kubernetes-minion-rcgd/130.211.122.180 name=redis,role=slave Running 38 seconds
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redis-slave gurpartap/redis Running 36 seconds
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```
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You will see a single redis master pod and two redis slave pods.
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### Step Four: Create the redis slave service.
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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`
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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.
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Now that you have created the service specification, create it in your cluster with the `kubectl` CLI:
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```shell
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$ kubectl create -f examples/guestbook-go/redis-slave-service.json
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$ kubectl get services
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NAME LABELS SELECTOR IP(S) PORT(S)
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redis-master name=redis,role=master name=redis,role=master 10.0.11.173 6379/TCP
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redis-slave name=redis,role=slave name=redis,role=slave 10.0.234.24 6379/TCP
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```
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### Step Five: Create the guestbook pod.
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This is a simple Go net/http ([negroni](https://github.com/codegangsta/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.
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The pod is described in the file `examples/guestbook-go/guestbook-controller.json`. Using this file, you can turn up your guestbook with:
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```shell
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$ kubectl create -f examples/guestbook-go/guestbook-controller.json
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$ kubectl get replicationControllers
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CONTROLLER CONTAINER(S) IMAGE(S) SELECTOR REPLICAS
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guestbook guestbook kubernetes/guestbook:v2 name=guestbook 3
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redis-master redis-master gurpartap/redis name=redis,role=master 1
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redis-slave redis-slave gurpartap/redis name=redis,role=slave 2
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```
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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:
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```shell
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POD IP CONTAINER(S) IMAGE(S) HOST LABELS STATUS CREATED MESSAGE
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guestbook-1xzms 10.244.1.6 kubernetes-minion-q6w5/23.236.54.97 name=guestbook Running 40 seconds
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guestbook kubernetes/guestbook:v2 Running 35 seconds
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guestbook-9ksu4 10.244.0.5 kubernetes-minion-mluf/104.197.10.10 name=guestbook Running 40 seconds
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guestbook kubernetes/guestbook:v2 Running 34 seconds
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guestbook-lycwm 10.244.1.7 kubernetes-minion-q6w5/23.236.54.97 name=guestbook Running 40 seconds
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guestbook kubernetes/guestbook:v2 Running 35 seconds
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redis-master-y06lj 10.244.3.4 kubernetes-minion-bz1p/104.154.61.231 name=redis,role=master Running 8 minutes
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redis-master gurpartap/redis Running 8 minutes
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redis-slave-3psic 10.244.0.4 kubernetes-minion-mluf/104.197.10.10 name=redis,role=slave Running 3 minutes
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redis-slave gurpartap/redis Running 3 minutes
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redis-slave-qtigf 10.244.2.4 kubernetes-minion-rcgd/130.211.122.180 name=redis,role=slave Running 3 minutes
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redis-slave gurpartap/redis Running 3 minutes
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```
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You will see a single redis master pod, two redis slaves, and three guestbook pods.
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### Step Six: Create the guestbook service.
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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 `"type": "LoadBalancer"` for the service.
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```shell
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$ kubectl create -f examples/guestbook-go/guestbook-service.json
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$ kubectl get services
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NAME LABELS SELECTOR IP(S) PORT(S)
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guestbook name=guestbook name=guestbook 10.0.114.109 3000/TCP
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redis-master name=redis,role=master name=redis,role=master 10.0.11.173 6379/TCP
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redis-slave name=redis,role=slave name=redis,role=slave 10.0.234.24 6379/TCP
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```
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To play with the service itself, find the external IP of the load balancer:
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```shell
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$ kubectl get services guestbook -o template --template='{{(index .status.loadBalancer.ingress 0).ip}}'
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104.154.63.66$
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```
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and then visit port 3000 of that IP address e.g. `http://104.154.63.66:3000`.
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**NOTE:** You may need to open the firewall for port 3000 using the [console][cloud-console] or the `gcloud` tool. The following command will allow traffic from any source to instances tagged `kubernetes-minion`:
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```shell
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$ gcloud compute firewall-rules create --allow=tcp:3000 --target-tags=kubernetes-minion kubernetes-minion-3000
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```
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If you are running Kubernetes locally, you can just visit http://localhost:3000
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For details about limiting traffic to specific sources, see the [GCE firewall documentation][gce-firewall-docs].
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[cloud-console]: https://console.developer.google.com
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[gce-firewall-docs]: https://cloud.google.com/compute/docs/networking#firewalls
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### Step Seven: Cleanup
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You should delete the service which will remove any associated resources that were created e.g. load balancers, forwarding rules and target pools. All the resources (replication controllers and service) can be deleted with a single command:
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```shell
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$ kubectl delete -f examples/guestbook-go
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guestbook-controller
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guestbook
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redis-master-controller
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redis-master
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redis-slave-controller
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redis-slave
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```
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To turn down a Kubernetes cluster:
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```shell
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$ cluster/kube-down.sh
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```
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[]()
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