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user-guide: Add memcached-operator walkthrough
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‎doc/milestone/user_guide.md‎

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# Getting Started
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# User Guide
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This guide walks through an example of building a simple memcached-operator using tools and libraries provided by the Operator SDK.
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## Prerequisites
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- [dep][dep_tool] version v0.4.1+.
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- [go][go_tool] version v1.10+.
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- [docker][docker_tool] version 17.03+.
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- Access to a public registry such as quay.io.
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- [kubectl][kubectl_tool] version v1.9.0+.
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- Access to a kubernetes v.1.9.0+ cluster.
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**Note**: This guide uses [minikube][minikube_tool] version v0.25.0+ as the local kubernetes cluster and quay.io for the public registry.
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## Installing Operator SDK CLI
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## Install the Operator SDK CLI
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The Operator SDK comes with a CLI tool that manages the development lifecycle. It helps create the project scaffolding, preprocess custom resource API to generate Kubernetes related code, and generate deployment scripts.
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The Operator SDK has a CLI tool that helps the developer to create, build, and deploy a new operator project.
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Checkout the desired release tag and install the SDK CLI tool:
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```
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git checkout tags/v0.0.2
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go install github.com/coreos/operator-sdk/commands/operator-sdk
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$ git checkout tags/v0.0.2
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$ go install github.com/coreos/operator-sdk/commands/operator-sdk
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```
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This installs the CLI binary `operator-sdk` at `$GOPATH/bin`.
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## Create a new project
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Use the CLI to create a new memcached-operator project:
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```
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$ cd $GOPATH/src/github.com/example-inc/
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$ operator-sdk new memcached-operator --api-version=cache.example.com/v1alpha1 --kind=Memcached
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$ cd memcached-operator
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```
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This creates the memcached-operator project specifically for watching the Memcached resource with APIVersion `cache.example.com/v1apha1` and Kind `Memcached`.
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To learn more about the project directory structure, see [project layout][layout_doc] doc.
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## Customize the operator logic
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For this example the memcached-operator will execute the following reconciliation logic for each `Memcached` CR:
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- Create a memcached Deployment if it doesn't exist
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- Ensure that the Deployment size is the same as specified by the `Memcached` CR spec
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- Update the `Memcached` CR status with the names of the memcached pods
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### Watch the Memcached CR
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By default, the memcached-operator watches `Memcached` resource events as shown in `cmd/memcached-operator/main.go`.
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```Go
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func main() {
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sdk.Watch("cache.example.com/v1alpha1", "Memcached", "default")
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sdk.Handle(stub.NewHandler())
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sdk.Run(context.TODO())
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}
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```
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### Define the Memcached spec and status
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Modify the spec and status of the `Memcached` CR at `pkg/apis/cache/v1alpha1/types.go`:
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```Go
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type MemcachedSpec struct {
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// Size is the size of the memcached deployment
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Size int32 `json:"size"`
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}
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type MemcachedStatus struct {
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// Nodes are the names of the memcached pods
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Nodes []string `json:"nodes"`
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}
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```
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Update the generated code for the CR:
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```
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$ operator-sdk generate k8s
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```
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### Define the Handler
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The reconciliation loop for an event is defined in the `Handle()` function at `pkg/stub/handler.go`.
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Replace the default handler with the reference [memcached handler][memcached_handler] implementation.
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> Note: The provided handler implementation is only meant to demonstrate the use of the SDK APIs and is not representative of the best practices of a reconciliation loop.
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### Build and run the operator
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Build the memcached-operator image and push it to a registry:
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```
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$ operator-sdk build quay.io/example/memcached-operator:v0.0.1
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$ docker push quay.io/example/memcached-operator:v0.0.1
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```
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This will install the CLI binary `operator-sdk` at `$GOPATH/bin`.
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Kubernetes deployment manifests are generated in `deploy/operator.yaml`. The deployment image is set to the container image specified above.
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## Creating a new project
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Deploy the memcached-operator:
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TODO
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```
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kubectl create -f deploy/rbac.yaml
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kubectl create -f deploy/operator.yaml
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```
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Verify that the memcached-operator is up and running:
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```
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$ kubectl get deployment
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NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE
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memcached-operator 1 1 1 1 1m
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```
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### Create a Memcached CR
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Run the following command to create a `Memcached` custom resource:
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```sh
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$ cat <<EOF | kubectl apply -f -
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apiVersion: "cache.example.com/v1alpha1"
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kind: "Memcached"
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metadata:
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name: "example-memcached"
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spec:
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size: 3
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EOF
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```
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Ensure that the memcached-operator creates the deployment for the CR:
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```
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$ kubectl get deployment
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NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE
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memcached-operator 1 1 1 1 2m
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example-memcached 3 3 3 3 1m
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```
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Check the pods and CR status to confirm the status is updated with the memcached pod names:
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```
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$ kubectl get pods
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NAME READY STATUS RESTARTS AGE
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example-memcached-6fd7c98d8-7dqdr 1/1 Running 0 1m
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example-memcached-6fd7c98d8-g5k7v 1/1 Running 0 1m
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example-memcached-6fd7c98d8-m7vn7 1/1 Running 0 1m
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memcached-operator-7cc7cfdf86-vvjqk 1/1 Running 0 2m
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```
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```
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$ kubectl get memcached/example-memcached -o yaml
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apiVersion: cache.example.com/v1alpha1
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kind: Memcached
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metadata:
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clusterName: ""
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creationTimestamp: 2018-03-31T22:51:08Z
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generation: 0
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name: example-memcached
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namespace: default
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resourceVersion: "245453"
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selfLink: /apis/cache.example.com/v1alpha1/namespaces/default/memcacheds/example-memcached
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uid: 0026cc97-3536-11e8-bd83-0800274106a1
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spec:
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size: 3
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status:
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nodes:
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- example-memcached-6fd7c98d8-7dqdr
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- example-memcached-6fd7c98d8-g5k7v
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- example-memcached-6fd7c98d8-m7vn7
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```
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### Update the size
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Change the `spec.size` field in the memcached CR from 3 to 4:
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```
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$ kubectl get memcached/example-memcached -o yaml | sed 's|size: 3|size: 4|g' | kubectl apply -f -
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```
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Confirm that the operator changes the deployment size:
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```
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$ kubectl get deployment
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NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE
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example-memcached 4 4 4 4 5m
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```
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### Cleanup
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Clean up the resources:
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```
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kubectl delete memcached example-memcached
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kubectl delete -f deploy/operator.yaml
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```
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[scaffold_doc]:./doc/project_layout.md
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[mc_protocol]:https://github.com/memcached/memcached/blob/master/doc/protocol.txt
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[memcached_handler]: example/memcached-operator/handler.go
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[layout_doc]:./doc/project_layout.md
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[dep_tool]:https://golang.github.io/dep/docs/installation.html
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[go_tool]:https://golang.org/dl/
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[docker_tool]:https://docs.docker.com/install/
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[kubectl_tool]:https://kubernetes.io/docs/tasks/tools/install-kubectl/
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[minikube_tool]:https://github.com/kubernetes/minikube#installation
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[operator_link]:https://coreos.com/operators/
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[design_docs]:./doc/design
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[minikube_tool]:https://github.com/kubernetes/minikube#installation

‎example/memcached-operator/handler.go‎

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// TODO

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