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Tutorial

Canary deployment with Jenkins and Istio

Learn how to use Jenkins running on Kubernetes to conduct Canary deployments

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By Ryan Moe
Published October 4, 2018

In this tutorial, we’ll show you how to use Jenkins that is running on Kubernetes to then run canary deployments. We will create a simple web application, deploy it to Kubernetes, and then update the application. The updated application will be deployed for a small subset of users. Once we’re satisifed with our app deployment, we’ll see whether the updated application works as expected and then we’ll deploy it for all users.

Steps

  1. Prerequisites
  2. Sample application
  3. Create the pipeline
  4. Deploy Canary branch
  5. Deploy master

1. Prerequisites

Here’s what you’ll need to get started with this tutorial:

  1. Install Istio on your Kubernetes cluster
  2. Install Jenkins on the Kubernetes and Istio cluster
  3. A git repository

Configure Jenkins and containers

First, we need to disable automatic sidecar injection for the Jenkins worker pods.

Navigate to Manage Jenkins > Configure System > Cloud > Kubernetes Pod Template, add a new Pod Annotation with a key of sidecar.istio.io/inject and a value of false.

Pod Annotation

Next, configure these three additional containers in the “Kubernetes Pod Template” section of the Jenkins configuration:

  1. A Python container using the image python:3-alpine. This container is used to install the application for running tests and building the image in a subsequent step.

    Python container

  2. A Docker container using the image docker. This container is used to build the image and push it to the IBM Container Registry. Additionally, two environment variables must be defined. REGISTRY_TOKEN is a token which allows access to the IBM Container Registry and IMAGE_REGISTRY is the container registry path. For IBM Container Registry it is registry.ng.bluemix.net/<your namespace>.

    Docker container

  3. A kubectl container using the image lachlanevenson/k8s-kubectl. This container is used to deploy the application to Kubernetes.

    Kubectl container

2. Sample application

A Flask application which listens on port 8080 and returns its version will be used to demonstrate a canary deployment.

from flask import Flask

version = b"0.1.0"
app = Flask(__name__)

@app.route("/")
def hello():
    return version

if __name__ == '__main__':
    app.run(host='0.0.0.0', port=8080, debug=True)

Create a simple test in tests/test_version.py that can be run in the ‘test’ step of the pipeline:

import pytest
import app

@pytest.fixture
def client():
    client = app.app.test_client()
    yield client


def test_version(client):
    req = client.get('/')
    assert req.data == app.version

Create the deployment manifests

Create a new directory named deployment and create app.yaml inside it.

kind: Deployment
  metadata:
name: sampleapp
spec:
  replicas: 1
  template:
    metadata:
      labels:
        app: sampleapp
    spec:
      containers:
      - name: sampleapp
        image: registry.ng.bluemix.net/<namespace>/sampleapp:v1
        imagePullPolicy: Always
---
apiVersion: v1
kind: Service
metadata:
  name: samplepp
spec:
  type: LoadBalancer
  ports:
  - port: 8080
    name: http
  selector:
    app: sampleapp

The canary deployment is the same as the one in app.yaml except the name is different and no service needs to be defined.

kind: Deployment
  metadata:
name: sampleapp-canary
spec:
  replicas: 1
  template:
    metadata:
      labels:
        app: sampleapp
    spec:
      containers:
      - name: sampleapp
        image: registry.ng.bluemix.net/<namespace>/sampleapp:canary
        imagePullPolicy: Always

Initial deployment of the sample application

Build a Docker image of the application from the following Dockerfile and then deploy it to the cluster:

FROM python:3-alpine
COPY requirements.txt app.py /
RUN pip install -r requirements.txt

EXPOSE 8080
CMD ["python", "app.py"]

$ docker build -t registry.ng.bluemix.net/<namespace>/sampleapp:v1 .
$ docker push registry.ng.bluemix.net/<namespace>/sampleapp:v1
$ kubectl apply -f deployment/app.yaml

This creates a Service and a Deployment. To access the service from outside the cluster create a Gateway and VirtualService with Istio.

apiVersion: networking.istio.io/v1alpha3
kind: Gateway
metadata:
  name: sampleapp-gateway
spec:
  selector:
    istio: ingressgateway
  servers:
  - port:
      number: 80
      name: http
      protocol: HTTP
    hosts:
    - "*"
---
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: sampleapp
spec:
  hosts:
  - "*"
  gateways:
  - sampleapp-gateway
  http:
  - match:
    - uri:
        prefix: /
    route:
    - destination:
        host: sampleapp
        subset: prod
        port:
          number: 8080
      weight: $PROD_WEIGHT
    - destination:
        host: sampleapp
        subset: canary
        port:
          number: 8080
      weight: $CANARY_WEIGHT
---
apiVersion: networking.istio.io/v1alpha3
kind: DestinationRule
metadata:
  name: sampleapp
spec:
  host: sampleapp
  subsets:
  - name: prod
    labels:
      version: prod
  - name: canary
    labels:
      version: canary

Deploy the Istio configuration. Because there is no canary deployment yet, set the canary weight to 0 and the production weight to 100.

$ PROD_WEIGHT=100 CANARY_WEIGHT=0 envsubst < deployment/istio.yaml | kubectl apply -f -

Now let’s find the ingress IP address.

$ export INGRESS_HOST=$(kubectl -n istio-system get service istio-ingressgateway -o jsonpath='{.status.loadBalancer.ingress[0].ip}')
$ curl http://$INGRESS_HOST
0.1.0
$

Commit what we’ve done so far.

$ git add Dockerfile app.py deployment/
$ git commit -m "v1"
$ git push origin master

3. Create the pipeline

Create a multibranch pipeline. In Branch Sources, add a new Git source and add the link to your sample application repository. Under “Scan Multibranch Pipeline Triggers,” check the box that says Periodically if not otherwise run and set the interval to 1 minute.

By default, this will look for the pipeline definition in a Jenkinsfile in the root of the project.

def gitSHA

pipeline {
  agent {
    kubernetes {
      defaultContainer 'jnlp'
    }
  }

  stages {
    stage('Checkout') {
      steps {
        checkout scm
        script {
          gitSHA = sh(returnStdout: true, script: 'git rev-parse --short HEAD')
        }
      }
    }
    stage('Install') {
      steps {
        container('python') {
          sh 'pip install -r requirements.txt'
        }
      }
    }
    stage('Test') {
      steps {
        container('python') {
          sh 'pytest'
        }
      }
    }
    stage('Build') {
      environment {
        TAG = "$gitSHA"
      }
      steps {
        container('docker') {
          sh 'docker login -u token -p ${REGISTRY_TOKEN} registry.ng.bluemix.net'
          sh 'docker build -t $IMAGE_REGISTRY/sampleapp:$TAG .'
          sh 'docker push $IMAGE_REGISTRY/sampleapp:$TAG'
        }
      }
    }
    stage('Deploy Canary') {
      when { branch 'canary' }
      steps {
        container('kubectl') {
          sh 'apk update && apk add gettext'
          sh "export TAG=$gitSHA" + 'envsubst < deployment/canary.yaml | kubectl apply -f -'
          sh "export PROD_WEIGHT=95 CANARY_WEIGHT=5" + 'envsubst < deployment/istio.yaml | kubectl apply -f -'
        }
      }
    }
    stage('Deploy Production') {
      when { branch 'master' }
      steps {
        container('kubectl') {
          sh 'apk update && apk add gettext'
          sh "export TAG=$gitSHA" + 'envsubst < deployment/app.yaml | kubectl apply -f -'
          sh "export PROD_WEIGHT=100 CANARY_WEIGHT=0" + 'envsubst < deployment/istio.yaml | kubectl apply -f -'
        }
      }
    }
  }
}

4. Deploy the Canary branch

First, create the Canary branch.

$ git checkout -b canary

Change the version in app.py to “0.2.0”:

app.version = b"0.2.0"

Commit the changes and push the branch.

$ git add app.py
$ git commit -m "v2"
$ git push origin canary

The pipeline will now run and create a new Kubernetes deployment named “canary.”

$ kubectl get deployment
NAME               DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
sampleapp          1         1         1            1           1h
sampleapp-canary   1         1         1            1           1h

Because both deployments have the same app: label, the service will load balance requests across the master and canary deployments. While this does work without Istio, it’s much less flexible.

For example, if you wanted to send 2 percent of all traffic to the canary deployment you would need to have a minimum of 50 replicas running. Istio decouples pod scaling and traffic routing.

The service should now return a combination of v1 and v2 results.

$ for i in $(seq 1 20); do curl http://$INGRESS_HOST/; echo; done
0.1.0
0.1.0
0.1.0
0.1.0
0.1.0
0.1.0
0.1.0
0.1.0
0.1.0
0.1.0
0.1.0
0.1.0
0.2.0
0.1.0
0.1.0
0.1.0
0.1.0
0.1.0
0.1.0
0.1.0

5. Deploy the master branch

Deploy the master branch:

$ git push master origin

Once changes are pushed to the master, Jenkins will build and deploy the master branch. It will change the route weight so that 100 percent of traffic will be going to the production deployment.

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