Merge pull request #80 from fluxcd/docs-webhook-receivers

Add webhook receivers guide to docs

docs/guides/webhook-receivers.md

@@ -0,0 +1,138 @@
+# Setup Webhook Receivers
+
+The GitOps toolkit controllers are by design **pull-based**.
+In order to notify the controllers about changes in Git or Helm repositories,
+you can setup webhooks and trigger a cluster reconciliation
+every time a source changes. Using webhook receivers, you can build **push-based**
+GitOps pipelines that react to external events.
+
+## Prerequisites
+
+To follow this guide you'll need a Kubernetes cluster with the GitOps 
+toolkit controllers installed on it.
+Please see the [get started guide](../get-started/index.md)
+or the [install command docs](../cmd/tk_install.md).
+
+The [notification controller](../components/notification/controller.md)
+can handle events coming from external systems
+(GitHub, GitLab, Bitbucket, Harbour, Jenkins, etc)
+and notify the GitOps toolkit controllers about source changes.
+The notification controller is part of the default toolkit installation.
+
+## Expose the webhook receiver
+
+In order to receive Git push or Helm chart upload events, you'll have to 
+expose the webhook receiver endpoint outside of your Kubernetes cluster on 
+a public address.
+
+The notification controller handles webhook requests on port `9292`.
+This port can be used to create a Kubernetes LoadBalancer Service or Ingress.
+
+Create a `LoadBalancer` service:
+
+```yaml
+apiVersion: v1
+kind: Service
+metadata:
+  name: receiver
+  namespace: gitops-system
+spec:
+  type: LoadBalancer
+  selector:
+    app: notification-controller
+  ports:
+    - name: http
+      port: 80
+      protocol: TCP
+      targetPort: 9292
+```
+
+Wait for Kubernetes to assign a public address with:
+
+```sh
+watch kubectl -n gitops-system get svc/receiver
+``` 
+
+## Define a Git repository
+
+Create a Git source pointing to a GitHub repository that you have control over:
+
+```yaml
+apiVersion: source.fluxcd.io/v1alpha1
+kind: GitRepository
+metadata:
+  name: webapp
+  namespace: gitops-system
+spec:
+  interval: 60m
+  url: https://github.com/<GH-ORG>/<GH-REPO>
+  ref:
+    branch: master
+```
+
+!!! hint "Authentication"
+    SSH or token based authentication can be configured for private repositories.
+    See the [GitRepository CRD docs](../components/source/gitrepositories.md) for more details.
+
+## Define a Git repository receiver
+
+First generate a random string and create a secret with a `token` field:
+
+```sh
+TOKEN=$(head -c 12 /dev/urandom | shasum | cut -d ' ' -f1)
+echo $TOKEN
+
+kubectl -n gitops-system create secret generic webhook-token \	
+--from-literal=token=$TOKEN
+```
+
+Create a receiver for GitHub and specify the `GitRepository` object:
+
+```yaml
+apiVersion: notification.fluxcd.io/v1alpha1
+kind: Receiver
+metadata:
+  name: webapp
+  namespace: gitops-system
+spec:
+  type: github
+  events:
+    - "ping"
+    - "push"
+  secretRef:
+    name: webhook-token
+  resources:
+    - kind: GitRepository
+      name: webapp
+```
+
+!!! hint "Note"
+    Besides GitHub, you can define receivers for **GitLab**, **Bitbucket**, **Harbour**
+    and any other system that supports webhooks e.g. Jenkins, CircleCI, etc.
+    See the [Receiver CRD docs](../components/notification/receiver.md) for more details.
+
+The notification controller generates a unique URL using the provided token and the receiver name/namespace.
+
+Find the URL with:
+
+```console
+$ kubectl -n gitops-system get receiver/webapp
+
+NAME     READY   STATUS
+webapp   True    Receiver initialised with URL: /hook/bed6d00b5555b1603e1f59b94d7fdbca58089cb5663633fb83f2815dc626d92b
+```
+
+On GitHub, navigate to your repository and click on the "Add webhook" button under "Settings/Webhooks". 
+Fill the form with:
+
+* **Payload URL**: compose the address using the receiver LB and the generated URL `http://<LoadBalancerAddress>/<ReceiverURL>`
+* **Secret**: use the `token` string
+
+With the above settings, when you push a commit to the repository, the following happens:
+
+* GitHub sends the Git push event to the receiver address
+* Notification controller validates the authenticity of the payload using HMAC
+* Source controller is notified about the changes
+* Source controller pulls the changes into the cluster and updates the `GitRepository` revision
+* Kustomize controller is notified about the revision change
+* Kustomize controller reconciles all the `Kustomizations` that reference the `GitRepository` object

mkdocs.yml

@@ -41,6 +41,7 @@ nav:
   - Get Started: get-started/index.md
   - Guides:
       - Setup Notifications: guides/notifications.md
+      - Setup Webhook Receivers: guides/webhook-receivers.md
   - Toolkit Components:
     - Source Controller:
       - Overview: components/source/controller.md
@@ -53,10 +54,10 @@ nav:
       - Kustomize API Reference: components/kustomize/api.md
     - Notification Controller:
         - Overview: components/notification/controller.md
+        - Event: components/notification/event.md
         - Provider CRD: components/notification/provider.md
         - Alert CRD: components/notification/alert.md
-        - Event: components/notification/event.md
-        - Webhook Receiver: components/notification/receiver.md
+        - Receiver CRD: components/notification/receiver.md
         - Notification API Reference: components/notification/api.md
   - Toolkit CLI:
     - Overview: cmd/tk.md