The application Lab📜

In this lab, you will deploy an application to your mesh.

The application consists of two microservices, web-frontend and customers.

Tip

The official Istio docs canonical example is the [BookInfo application](https://istio.io/latest/docs/examples/bookinfo/){target=_blank}.

For this workshop we felt that an application involving fewer microservices would be more clear.

The customers service exposes a REST endpoint that returns a list of customers in JSON format. The web-frontend calls customers to retrieve the list, which it uses to render to HTML.
The respective Docker images for these services have already been built and pushed to a Docker registry.
You will deploy the application to the default Kubernetes namespace.

Before proceeding, we must enable sidecar injection.

Enable automatic sidecar injection📜

There are two options for sidecar injection {target=_blank}: automatic and manual.

In this lab, we will use automatic injection, which involves labeling the pods’ namespace.

Label the default namespace.

kubectl label namespace default istio-injection=enabled

Verify that the label is applied:
```
kubectl get ns -Listio-injection
```

Deploy the application📜

Study the two Kubernetes yaml files: web-frontend.yaml and customers.yaml.

web-frontend.yaml

---
apiVersion: v1
kind: ServiceAccount
metadata:
  name: web-frontend
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: web-frontend
  labels:
    app: web-frontend
spec:
  replicas: 1
  selector:
    matchLabels:
      app: web-frontend
  template:
    metadata:
      labels:
        app: web-frontend
        version: v1
    spec:
      serviceAccountName: web-frontend
      containers:
        - image: gcr.io/tetratelabs/web-frontend:1.0.0
          imagePullPolicy: Always
          name: web
          ports:
            - containerPort: 8080
          env:
            - name: CUSTOMER_SERVICE_URL
              value: "http://customers.default.svc.cluster.local"
---
kind: Service
apiVersion: v1
metadata:
  name: web-frontend
  labels:
    app: web-frontend
spec:
  selector:
    app: web-frontend
  ports:
    - port: 80
      name: http
      targetPort: 8080

customers.yaml

---
apiVersion: v1
kind: ServiceAccount
metadata:
  name: customers
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: customers-v1
  labels:
    app: customers
    version: v1
spec:
  replicas: 1
  selector:
    matchLabels:
      app: customers
      version: v1
  template:
    metadata:
      labels:
        app: customers
        version: v1
    spec:
      serviceAccountName: customers
      containers:
        - image: gcr.io/tetratelabs/customers:1.0.0
          imagePullPolicy: Always
          name: svc
          ports:
            - containerPort: 3000
---
kind: Service
apiVersion: v1
metadata:
  name: customers
  labels:
    app: customers
spec:
  selector:
    app: customers
  ports:
    - port: 80
      name: http
      targetPort: 3000

Each file defines its corresponding deployment, service account, and ClusterIP service.

Apply the two files to your Kubernetes cluster.

kubectl apply -f customers.yaml

kubectl apply -f web-frontend.yaml

Confirm that:

Two pods are running, one for each service.
Each pod consists of two containers, the one running the service image plus the Envoy sidecar.
```
kubectl get pod
```

Question: How did each pod end up with two containers?

Istio installs a Kubernetes object known as a [mutating webhook admission controller](https://kubernetes.io/docs/reference/access-authn-authz/admission-controllers/){ target=_blank }: logic that intercepts Kubernetes object creation requests and that has the permission to alter (mutate) what ends up stored in etcd (the pod spec).

You can list the mutating webhooks in your Kubernetes cluster and confirm that the sidecar injector is present.

```{.shell .language-shell}
kubectl get mutatingwebhookconfigurations
```

Verify access to each service📜

We need to deploy a pod that runs a curl image to check the reachability of services within the cluster. The Istio distribution offers sleep, a sample app for this purpose.

Deploy sleep to the default namespace.

sleep.yaml

# Copyright Istio Authors
#
#   Licensed under the Apache License, Version 2.0 (the "License");
#   you may not use this file except in compliance with the License.
#   You may obtain a copy of the License at
#
#       http://www.apache.org/licenses/LICENSE-2.0
#
#   Unless required by applicable law or agreed to in writing, software
#   distributed under the License is distributed on an "AS IS" BASIS,
#   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
#   See the License for the specific language governing permissions and
#   limitations under the License.

##################################################################################################
# Sleep service
##################################################################################################
apiVersion: v1
kind: ServiceAccount
metadata:
  name: sleep
---
apiVersion: v1
kind: Service
metadata:
  name: sleep
  labels:
    app: sleep
    service: sleep
spec:
  ports:
  - port: 80
    name: http
  selector:
    app: sleep
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: sleep
spec:
  replicas: 1
  selector:
    matchLabels:
      app: sleep
  template:
    metadata:
      labels:
        app: sleep
    spec:
      terminationGracePeriodSeconds: 0
      serviceAccountName: sleep
      containers:
      - name: sleep
        image: curlimages/curl
        command: ["/bin/sleep", "infinity"]
        imagePullPolicy: IfNotPresent
        volumeMounts:
        - mountPath: /etc/sleep/tls
          name: secret-volume
      volumes:
      - name: secret-volume
        secret:
          secretName: sleep-secret
          optional: true
---

kubectl apply -f sleep.yaml

Capture the name of the sleep pod to an environment variable.

SLEEP_POD=$(kubectl get pod -l app=sleep -ojsonpath='{.items[0].metadata.name}')

Use the kubectl exec command to call the customers service.
```
kubectl exec $SLEEP_POD -it -- curl customers
```
The console output should show a list of customers in JSON format.
Call the web-frontend service
```
kubectl exec $SLEEP_POD -it -- curl web-frontend | head
```
The console output should show the start of an HTML page listing customers in an HTML table.

Next📜

Let’s explore exposing our mesh to inbound traffic using an ingress controller, now that we understand the interaction between the control and data planes.