Use blue-green deployment with Contour and PackageInstall for Supply Chain Choreographer

Blue-green deployment is an application delivery model that lets you gradually transfer user traffic from one version of your app to a later version while both are running in production. This topic outlines how to use blue-green deployment with Packages and PackageInstalls.

Prerequisites

To use blue-green deployment, you must complete the following prerequisites:

Complete the prerequisites in Configure and deploy to multiple environments with custom parameters.
Configure Carvel for your supply chain. See Carvel Package Supply Chains.
Configure Flux CD for your supply chain. See Deploy Package and PackageInstall using Flux CD Kustomization.

Add HTTPProxy to the blue deployment

The following example deploys a sample application, hello-app, to production using a Carvel Package and PackageInstall.

Create a Contour HTTPProxy resource to route traffic to the hello-app service from the URL www.hello-app.mycompany.com.
```
apiVersion: projectcontour.io/v1
kind: HTTPProxy
metadata:
  name: www
  namespace: prod
spec:
  virtualhost:
    fqdn: www.hello-app.mycompany.com
  routes:
    - conditions:
      - prefix: /
        services:
        - name: hello-app
          port: 8080
```
Note
The services names used in HTTPProxy has to match the names of existing services. In this case, the name hello-app matches the service installed by the PackageInstall.
Apply the HTTPProxy to your cluster:
```
kubectl apply -f httpproxy.yaml
```

Verify that the HTTPProxy is present and the route serves traffic to your app.

kubectl get HTTPProxy --namespace=prod

This displays a list of all the HTTPproxies in the current namespace with their current names.

$ kubectl get HTTPProxy --namespace=prod
NAMESPACE        NAME                     FQDN                                  TLS SECRET            STATUS    STATUS DESCRIPTION
prod             www                      www.hello-app.mycompany.com          hello-app-cert        valid     Valid HTTPProxy

Create the green deployment

After a new version of the package is added to the GitOps repository, create a new PackageInstall for v1.0.1 to create the green deployment.

Create a green-secret.yaml file with a secret that contains the following ytt overlay.

---
apiVersion: v1
kind: Secret
metadata:
  name: green-overlay-secret
  namespace: prod
stringData:
  custom-package-overlay.yaml: |
    #@ load("@ytt:overlay", "overlay")
    #@ kd = overlay.subset({"apiVersion":"apps/v1", "kind": "Deployment"})
    #@ ks = overlay.subset({"apiVersion":"v1", "kind": "Service"})
    #@ ki = overlay.subset({"apiVersion":"networking.k8s.io/v1", "kind": "Ingress"})
    #@ na = overlay.subset({"metadata":{"name":"hello-app"}})

    #@overlay/match by=overlay.and_op(kd, na)
    ---
    metadata:
      #@overlay/replace
      name: hello-app-green

    #@overlay/match by=overlay.and_op(ks, na)
    ---
    metadata:
      #@overlay/replace
      name: hello-app-green

    #@overlay/match by=overlay.and_op(ki, na)
    ---
    metadata:
      #@overlay/replace
      name: hello-app-green

This secret changes the names of the service and deployment in the Carvel Package to allow you to install another version of the app in the same namespace.

Apply the secret to your cluster by running:
```
kubectl apply -f green-secret.yaml
```

Create a parameter secret for the new PackageInstall:

---
apiVersion: v1
kind: Secret
metadata:
  name: green-dev-values
  namespace: prod
stringData:
  values.yaml: |
    ---
    replicas: 2
    hostname: hello-app-green.mycompany.com

Apply the parameter secret to your cluster by running:
```
kubectl apply -f green-dev-values.yaml
```

Create a PackageInstall to include the ext.packaging.carvel.dev/ytt-paths-from-secret-name.x annotation to reference your new overlay secret.

---
apiVersion: packaging.carvel.dev/v1alpha1
kind: PackageInstall
metadata:
  name: green.hello-app.dev.tap
  namespace: prod
  annotations:
    ext.packaging.carvel.dev/ytt-paths-from-secret-name.0: green-overlay-secret
spec:
  serviceAccountName: default
  packageRef:
    refName: hello-app.dev.tap
    versionSelection:
      constraints: "1.0.1"
  values:
  - secretRef:
      name: green-dev-values

Divide traffic between the blue and green deployments

Use the following procedure to divide traffic between your blue and green deployments.

Update the HTTPproxy created with the blue deployment to route traffic to both the blue and green deployments. The names of the services must match the names of the already created services.

---
apiVersion: projectcontour.io/v1
kind: HTTPProxy
metadata:
  name: www
  namespace: prod
spec:
  virtualhost:
    fqdn: www.hello-app.mycompany.com
  routes:
  - conditions:
    - prefix: /
      services:
      - name: hello-app-green
        port: 8080
        weight: 20
      - name: hello-app
        port: 8080
        weight: 80

Update the weights of traffic for each service by editing the HTTPProxy.
Access the service several times and confirm both versions are serving traffic in the same percentage.
```
curl -k https://www.hello-app.mycompany.com
```

After the new green app is ready to handle the complete load and the -green version is not required, use the following steps to remove the old version and rename the new version:

Ensure that all the traffic is using the correct version of the app. For example:

apiVersion: projectcontour.io/v1
kind: HTTPProxy
metadata:
  name: www
  namespace: prod
spec:
  virtualhost:
    fqdn: www.hello-app.mycompany.com
  routes:
    - conditions:
      - prefix: /
        services:
        - name: hello-app-green
          port: 8080
          weight: 100 # all traffic routed to the green app

Identify the name of the deployment and service that are part of the PackageInstall you no longer need:

kubectl get PackageInstall --namespace=prod

This displays a list of all the deployments and services in the current Kubernetes namespace, with their current names. For example:

NAME                     PACKAGE NAME       PACKAGE VERSION      DESCRIPTION
green.hello-app.dev.tap   hello-app.dev.tap   1.0.1            Reconcile succeeded
hello-app.dev.tap         hello-app.dev.tap   1.0.0            Reconcile succeeded

Delete the PackageInstall:

kubectl delete PackageInstall hello-app.dev.tap --namespace=prod

Rename the service and deployments without the green prefix. For example, update the overlay secret:

---
apiVersion: v1
kind: Secret
metadata:
  name: overlay-secret
  namespace: prod
stringData:
  custom-package-overlay.yaml: |
    #@ load("@ytt:overlay", "overlay")
    #@ load("@ytt:data", "data")

    #@ kd = overlay.subset({"apiVersion":"apps/v1", "kind": "Deployment"})
    #@ ks = overlay.subset({"apiVersion":"v1", "kind": "Service"})
    #@ ki = overlay.subset({"apiVersion":"networking.k8s.io/v1", "kind": "Ingress"})
    #@ na = overlay.subset({"metadata":{"name":"hello-app-green"}})

    #@overlay/match by=overlay.and_op(kd, na)
    ---
    metadata:
      #@overlay/replace
      name: hello-app
    #@overlay/match by=overlay.and_op(ks, na)
    ---
    metadata:
      #@overlay/replace
      name: hello-app
    #@overlay/match by=overlay.and_op(ki, na)
    ---
    metadata:
      #@overlay/replace
      name: hello-app
    ---
    apiVersion: projectcontour.io/v1
    kind: HTTPProxy
    metadata:
      name: www
      namespace: prod
    spec:
      virtualhost:
        fqdn: www.hello-app.mycompany.com
      routes:
        - conditions:
          - prefix: /
            services:
            - name: hello-app # note the name is changed back
              port: 8080
              weight: 100

Update your PackageInstall to include the ext.packaging.carvel.dev/ytt-paths-from-secret-name.x annotation to reference your new overlay secret. For example:

---
apiVersion: packaging.carvel.dev/v1alpha1
kind: PackageInstall
metadata:
  name: green.hello-app.dev.tap
  namespace: prod
  annotations:
    ext.packaging.carvel.dev/ytt-paths-from-secret-name.0: overlay-secret
spec:
  serviceAccountName: default
  packageRef:
    refName: hello-app.dev.tap
    versionSelection:
      constraints: "1.0.1"
  values:
  - secretRef:
      name: hello-app-values

After the deployment is complete, you can delete the secrets with the overlays.

Verify application

Verify the name of the deployment and service that are part of the PackageInstall by running:

kubectl get PackageInstall --namespace=prod

This displays a list of all the deployments and services in the current Kubernetes namespace with their current names. For example:

NAME                     PACKAGE NAME       PACKAGE VERSION      DESCRIPTION
hello-app.dev.tap       hello-app.dev.tap     1.0.1            Reconcile succeeded

The name is back to the original name and the version is 1.0.1.