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## GuestBook example
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This example shows how to build a simple multi-tier web application using Kubernetes and Docker.
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The example combines a web frontend, a redis master for storage and a replicated set of redis slaves.
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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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@@ -51,7 +49,7 @@ d5c458dabe50 gurpartap/redis:latest "/usr/local/bin/redi
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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' 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.
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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 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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@@ -63,7 +61,7 @@ NAME LABELS SELECTOR
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redis-master <none> name=redis,role=master 10.0.186.234 6379
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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. 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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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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@@ -79,7 +77,7 @@ redis-master-controller redis-master gurpartap/redis
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redis-slave-controller 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 Kubernetes service environment variables in the container environment. In particular, the redis slave is started with the following command:
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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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