Introduction

GitOps is a DevOps approach to maintain Kubernetes-based infrastructure as code in git, and operate it with git tools such as push, revert, pull request.

OneDev (https://github.com/theonedev/onedev) is an open source git repository server, with built-in CI/CD integration.
This tutorial explains how to set up OneDev to do GitOps in Kubernetes.

Set Up Kubernetes Cluster

Firstable we need a Kubernetes cluster. You may use an existing one, or just set up a new one. For this tutorial, we chose to use GKE (Google Kubernetes Engine).

Just follow the quick start to create a cluster. To save your money, the default pool with only one node is sufficient for our testing. For node image type, use the default Container-Optimized OS; for machine type, please select one with at least 8G mem. After creating the cluster, go ahead to configure kubectl to connect to the cluster following this guide.

To verify that things are working, run below command in your terminal to make sure it is successful:

$ kubectl cluster-info

Install OneDev into Kubernetes Cluster

Now that we have a working cluster. Lets deploy OneDev into the cluster to manage code of our demo project

1. Download OneDev k8s resources, extract it, and run below commands to deploy OneDev (note that OneDev by default will apply two persistent volumes to store data: one is of 100G to store git repositories, and another is of 10G to store database files. This setting can be adjusted via file k8s-resources/production/disk-settings.yaml if desired):
   

   $ cd k8s-resources/production$ kubectl apply -k .

2. After deployment, run below command to show external ip of OneDev service (may need to wait a while for external ip to be assigned):
   

   $ kubectl get services -n onedev

3. Open url http:// with your browser to set up OneDev. Wait a while and try again if OneDev is not ready

Add a Demo Project into OneDev

OneDev should be up and running. Lets set up a demo project now:

1. From OneDev projects page, add a project named gitops-demo

2. From the terminal, create a react project, and push to OneDev by running below commands (you need to have node.js environment. Refer to react documentation if you are not familiar with it):
   

   $ npx create-react-app gitops-demo $ cd gitops-demo$ git remote add origin http://<OneDev external ip>/gitops-demo$ git push --set-upstream origin master (use OneDev admin account created previously for authentication)

3. Refresh files page of the demo project in OneDev, and click the add build spec link as below:

   

4. From the build spec edit page, switch to Edit Source tab without adding any job and replace the source with below content (do not worry about the syntax. In most cases you only need to work with the GUI editor):
   

   version: 1jobs:- name: CI  image: node:10.16-alpine  commands:  - set -e  - ''  - apk add --update jq  - buildVersion=`jq -r '.version' package.json`  - echo "##onedev[SetBuildVersion '$buildVersion']"  - ''  - npm install -g yarn  - yarn install  - ''  - export CI=true  - yarn test  triggers:  - !BranchUpdateTrigger {}  retrieveSource: true  cloneCredential: !DefaultCredential {}  cpuRequirement: 250m  memoryRequirement: 128m  retryCondition: never  maxRetries: 3  retryDelay: 30  caches:  - key: npm-cache    path: /root/.npm  timeout: 3600

5. Save and commit the change. Our CI build should be running now as demonstrated below:

   

Set Up GitOps for the Demo Project

We now have a demo project with CI ability. Lets improve it to be able to deploy to Kubernetes:

1. To deploy to Kubernetes, we need to build and publish docker image of the demo project. We will use the official docker hub registry here. Please visit https://hub.docker.com)[https://hub.docker.com], login with your account, and create a public repository, say gitops-demo (OneDev also works with private repository, we create public repository here for simplicity purpose)

2. To be able to publish docker image to your repository, OneDev needs to know credential of your docker hub account. To do it, add a job secret in the demo project, give it a name, for instance, dockerhub-password, and input docker hub password as value of the secret

   

3. To deploy docker image of the demo project into Kubernetes, we need to give extra permissions to OneDev builds. To do it, create a file say gitops-demo-role.yaml in your terminal with below content:
   

   kind: ClusterRoleapiVersion: rbac.authorization.k8s.io/v1metadata:  name: gitops-demorules:- apiGroups: [""]  resources: ["services"]  verbs: ["get", "create"]- apiGroups: ["apps"]  resources: ["deployments"]  verbs: ["get", "patch", "create"]

   Then run below command to add the role into Kubernetes:
   

   $ kubectl apply -f gitops-demo-role.yaml

   After doing above, switch to job executors page in OneDev, delete the default auto-discover job executor, add a new Kubernetes executor, give it a name, and specify property Cluster Role as gitops-demo, leave all other fields untouched and save the executor

   

4. Since we need to build docker image of our demo project, lets add a Dockerfile in root of the project with below content:
   

   FROM nginx:1.19.5COPY build /usr/share/nginx/htmlEXPOSE 80

5. We deploy the demo project via Kubernetes resources, so continue to add a file k8s.yaml in root of the project with below content, and replace all occurrences of with name of your docker hub account:
   

   apiVersion: apps/v1kind: Deploymentmetadata:  name: gitops-demo  labels:    tier: gitops-demospec:  selector:    matchLabels:      tier: gitops-demo  strategy:    type: Recreate  template:    metadata:      name: gitops-demo      labels:        tier: gitops-demo    spec:      containers:      - name: gitops-demo        image: <your-dockerhub-account>/gitops-demo:imageTag        ports:        - containerPort: 80---apiVersion: v1kind: Servicemetadata:  name: gitops-demo  labels:    tier: gitops-demospec:  type: LoadBalancer  ports:  - name: http    port: 80    targetPort: 80    protocol: TCP  selector:    tier: gitops-demo

6. Edit build spec in OneDev (click file .onedev-buildspec.yaml from root of the project and then edit it), replace property image with docker:19.03.5, replace property commands with below content, and replace all occurrences of with name of your docker hub account.
   

   set -eapk add --update npm jq curlbuildVersion=`jq -r '.version' package.json`echo "##onedev[SetBuildVersion '$buildVersion']"npm install -g yarnyarn installexport CI=trueyarn testyarn builddocker build -t <your-dockerhub-account>/gitops-demo:@commit_hash@ .docker login -u <your-dockerhub-account> -p @secrets:dockerhub-password@docker push <your-dockerhub-account>/gitops-demo:@commit_hash@curl -o /usr/local/bin/kubectl -LO "https://storage.googleapis.com/kubernetes-release/release/$(curl -s https://storage.googleapis.com/kubernetes-release/release/stable.txt)/bin/linux/amd64/kubectl"chmod +x /usr/local/bin/kubectlsed -i "s/imageTag/@commit_hash@/g" k8s.yamlkubectl apply -f k8s.yaml -n default

7. Save and commit the change. OneDev will start to build and deploy the demo project. After build is successful, run below command to show external ip address of published demo service
   

   $ kubectl get service gitops-demo

   Open url http:// with your browser to show the deployed demo app.

8. Congrats! Youve successfully set up GitOps for the demo project. Whenever there is a new commit pushed to master branch, the CI job will be triggered to test, build, and redeploy the project. In case you want to revert to previous deployment, just run git revert master and push the change.

Multiple Deployment Environments

In our setup above, we deploy the demo project directly into the default namespace, which is not good. In real world, we may need to create multiple namespaces to cater deployment of multiple environments. Lets create two namespaces, one for test, and one for production:

$ kubectl create namespace test$ kubectl create namespace production

This tells OneDev to deploy our demo project into production namespace if build against master branch, and deploy into namespace identified by branch name otherwise. After committing the change, OneDev should be deploying the demo project into production namespace.

Now lets create the test branch to track deployments for test environment. After creating the branch, OneDev will start to deploy the demo project into test namespace.

To get Kubernetes printing external ip address of deployed demo service in specified namespaces, run below command:

kubectl get service -n <namespace>

Now from the commits page, we have a clear view of deployment status in different environments, and we can control deployments in different environments by pushing/merging into corresponding branches.

Thanks for reading!