docs: Add example for ArgoCD (#179)

Co-authored-by: Giovanni Liva <giovanni.liva@dynatrace.com>

examples/argo/Makefile

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+LFC_NAMESPACE ?= keptn-lifecycle-controller-system
+PODTATO_NAMESPACE ?= podtato-kubectl
+ARGO_NAMESPACE ?= argocd
+ARGO_VERSION ?= 2.4.14
+ARGO_SECRET = $(shell kubectl -n ${ARGO_NAMESPACE} get secret argocd-initial-admin-secret -o jsonpath="{.data.password}" | base64 -d; echo)
+
+.PHONY: install
+install:
+	@echo "-----------------------------------"
+	@echo "Create Namespace and install ArgoCD"
+	@echo "-----------------------------------"
+	kubectl create namespace $(ARGO_NAMESPACE)
+	kubectl apply -n argocd -f https://raw.githubusercontent.com/argoproj/argo-cd/v$(ARGO_VERSION)/manifests/install.yaml
+
+	@echo ""
+	@echo "-------------------------------"
+	@echo "Wait for Resources to get ready"
+	@echo "-------------------------------"
+	kubectl wait --for=condition=available deployment/argocd-dex-server -n "$(ARGO_NAMESPACE)" --timeout=120s
+	kubectl wait --for=condition=available deployment/argocd-redis -n "$(ARGO_NAMESPACE)" --timeout=120s
+	kubectl wait --for=condition=available deployment/argocd-repo-server -n "$(ARGO_NAMESPACE)" --timeout=120s
+	kubectl wait --for=condition=available deployment/argocd-server  -n "$(ARGO_NAMESPACE)" --timeout=120s
+
+
+	@echo ""
+	@echo "#######################################################"
+	@echo "ArgoCD Demo installed"
+	@echo "- Get Admin Password: make argo-get-password"
+	@echo "- Port-Forward ArgoCD: make port-forward-argocd"
+	@echo "- Get Argo CLI: https://argo-cd.readthedocs.io/en/stable/cli_installation/"
+	@echo "- Configure ArgoCD CLI (needs port-forward): make argo-configure-cli"
+	@echo "- Install PodTatoHead via ArgoCD: make argo-install-podtatohead"	
+	@echo "#######################################################"
+
+.PHONY: argo-configure-cli
+argo-configure-cli:
+	@argocd login localhost:8080 --username admin --password $(ARGO_SECRET) --insecure
+
+.PHONY: argo-get-password
+argo-get-password:
+	@echo $(ARGO_SECRET)
+
+.PHONY: port-forward-argocd
+port-forward-argocd:
+	@echo ""
+	@echo "Open ArgoCD in your Browser: http://localhost:8080"
+	@echo "CTRL-c to stop port-forward"
+
+	@echo ""
+	kubectl port-forward svc/argocd-server -n "$(ARGO_NAMESPACE)" 8080:443
+
+.PHONY: argo-install-podtatohead
+argo-install-podtatohead:
+	@echo ""
+	kubectl apply -f config/app.yaml -n "$(ARGO_NAMESPACE)" 
+
+.PHONY: uninstall
+uninstall:
+	kubectl delete -n $(ARGO_VERSION) -f https://raw.githubusercontent.com/argoproj/argo-cd/v$(ARGO_VERSION)/manifests/install.yaml --ignore-not-found=true
+	kubectl delete namespace $(ARGO_NAMESPACE) --ignore-not-found=true
+	@echo ""
+	@echo "##########################"
+	@echo "Argo Demo deleted"
+	@echo "##########################"

examples/argo/README.md

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+# Deploying an application using the Keptn Lifecycle Controller and ArgoCD
+
+In this example, we will show you how to install our sample application *podtatohead* using the Keptn Lifecycle Controller and [ArgoCD](https://argo-cd.readthedocs.io/en/stable/).
+
+# TL;DR
+* You can install ArgoCD using: `make install`
+* Afterward, you can fetch the secret for the ArgoCD CLI using: `make argo-get-password`
+* Then you can port-forward the ArgoUI using: `make argo-port-forward`
+  * Alternatively, you can access Argo using the CLI, configure it using `make argo-configure-cli`
+* Deploy the PodTatoHead Demo Application: `make argo-install-podtatohead`
+* Watch the progress on your ArgoUI: `http://localhost:8080`
+
+## Prerequisites:
+This tutorial assumes, that you already installed the Keptn Lifecycle Controller (see https://github.com/keptn-sandbox/lifecycle-service). Furthermore, you have to install ArgoCD, as in the following their [installation instructions](https://argoproj.github.io/argo-cd/getting_started/).
+
+### Install ArgoCD
+If you don't have an already existing installation of ArgoCD, you can install it using the following commands:
+```shell
+kubectl create namespace argocd
+kubectl apply -n argocd -f https://raw.githubusercontent.com/argoproj/argo-cd/latest/manifests/install.yaml
+```
+
+With these commands, ArgoCD will be installed in the `argocd` namespace.
+
+After that, you can find the password for ArgoCD using the following command:
+```shell
+kubectl -n argocd get secret argocd-initial-admin-secret -o jsonpath="{.data.password}" | base64 -d
+```
+
+### Port-Forward ArgoCD and access the UI
+To access the ArgoCD UI, you can port-forward the ArgoCD service using the following command:
+```shell
+kubectl port-forward svc/argocd-server -n argocd 8080:443
+```
+Then you can access the UI using http://localhost:8080.
+
+## Installing the Demo Application
+To install the demo application, you can use the following command:
+```shell
+kubectl apply -f https://raw.githubusercontent.com/keptn-sandbox/lifecycle-service/main/examples/argo/config/app.yaml
+```
+
+You will see that the application will be deployed using ArgoCD. You can watch the progress on the ArgoCD UI and should see the following:
+![img.png](assets/argo-screen.png)
+
+In the meanwhile you can watch the progress of the deployment using:
+> `kubectl get pods -n podtato-kubectl`
+  * See that the pods are pending until the pre-deployment tasks have passed
+  * Pre-Deployment Tasks are started
+  * Pods get scheduled
+
+> `kubectl get keptnworkloadinstances -n podtato-kubectl`
+  * Get the current status of the workloads
+  * See in which phase your workload deployments are at the moment
+
+> `kubectl get keptnapplicationversions -n podtato-kubectl`
+    * Get the current status of the application
+    * See in which phase your application deployment is at the moment
+
+After some time all resources should be in a succeeded state. In the Argo-UI you will see that the application is in sync.

examples/argo/config/app.yaml

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+apiVersion: argoproj.io/v1alpha1
+kind: Application
+metadata:
+  name: podtato-head 
+  namespace: argocd
+spec:
+  project: default
+  source:
+    repoURL: https://github.com/thschue/lifecycle-controller 
+    targetRevision: main
+    path: examples/podtatohead-deployment
+  destination: 
+    server: https://kubernetes.default.svc
+    namespace: podtato-kubectl
+  syncPolicy:
+    automated:
+      selfHeal: true
+      prune: true