GitOps for Devs - Part 2: Navigating the Code

We're continuing our exploration of GitOps with ArgoCD. In the first part, we got a grasp of GitOps basics and set up an example app called Album-App. Now, let's explore the repositories that drive this application:

The Two Repositories

1. Application Code - This contains the actual code for both the Frontend and Backend applications.
   • Backend: A simple REST API written in Go, accessible on port 8080.
   • Frontend: A React application that communicates with the backend.
2. Config Repo - Hosts Helm charts defining the application's infrastructure.

Application Repository

The application repository contains the code for both Frontend and Backend applications.

Backend

The backend application itself is a simple REST API written in Go.

The application exposes port 8080.

You can test the application on your docker environment by,

docker run -p 8080:8080 ghcr.io/krishanthisera/album-app-backend

Once the container is up click here to see API documentation.

Frontend

The Frontend is a React application that talks to the backend.

To test the application locally,

docker run -p 3000:3000 ghcr.io/krishanthisera/album-app-frontend

Please note that the backend app should be running on port 8080.

Configuration Repository

The Config Repo contains Helm charts that define the application infrastructure.

Here we have four helm charts ⎈,

1. root-app: Acts as ArgoCD's entry point, managing and deploying the whole application stack.
2. apps: Contains ArgoCD applications.
3. frontend and backend: Helm charts for respective Kubernetes deployments.

Understanding Root App

As the name suggests, the root app is the entry point for ArgoCD to manage and deploy the entire application stack.

apiVersion: argoproj.io/v1alpha1
kind: Application
metadata:
  name: root-app
  namespace: argocd
  finalizers:
  - resources-finalizer.argocd.argoproj.io
spec:
  destination:
    namespace: album-app
    name: in-cluster
  project: default
  source:
    path: apps
    repoURL: https://github.com/krishanthisera/album-app-config
    targetRevision: HEAD

Here's a snippet:

• Destination: Specifies where the application will be deployed (namespace and cluster).

• Project: Defines the ArgoCD project the application belongs to. Projects offer a way to group and organize applications based on shared policies, permissions, and settings.
  

  # Default ArgoCD Project
  apiVersion: argoproj.io/v1alpha1
  kind: AppProject
  metadata:
    name: default  # Name of the project
    namespace: argocd  # Namespace where the project resides
  spec:
    clusterResourceWhitelist:  # Whitelisted cluster resources
    - group: '*'  # All resource groups allowed
      kind: '*'   # All resource kinds allowed
    destinations:  # Deployment destinations
    - namespace: '*'  # Deploy to all namespaces
      server: '*'  # Deploy to all servers
    sourceRepos:  # Allowed source repositories
    - '*'  # Allow all repositories
  

• Source: Indicates the source of the application's configuration (Git repository URL, path, and target revision).

Here the root-app points to the /apps directory in the config repo.

Apps Helm Chart

As mentioned in the previous article, here we follow the ArgoCD App-of-Apps pattern.

Above are ArgoCD application resources residing in the argocd namespace. They define their respective apps' deployment targets, projects, and source repositories.

# Backend Application
apiVersion: argoproj.io/v1alpha1
kind: Application
metadata:
  name: album-app-backend  # Name of the ArgoCD application
  namespace: argocd  # Namespace where the ArgoCD application resides
  finalizers:
    - resources-finalizer.argocd.argoproj.io  # Action to be taken when deleting the resource
spec:
  destination:
    namespace: album-app  # Deployment target namespace for the backend application
    server: https://kubernetes.default.svc  # Kubernetes server for deployment
  project: album-app  # Project to which the backend application belongs
  source:
    path: backend  # Directory containing backend code/configuration
    repoURL: https://github.com/krishanthisera/album-app-config  # Git repository URL
    targetRevision: HEAD  # Target revision of the repository

---
# Frontend Application
apiVersion: argoproj.io/v1alpha1
kind: Application
metadata:
  name: album-app-frontend  # Name of the ArgoCD application
  namespace: argocd  # Namespace where the ArgoCD application resides
  finalizers:
    - resources-finalizer.argocd.argoproj.io  # Action to be taken when deleting the resource
spec:
  destination:
    namespace: album-app  # Deployment target namespace for the frontend application
    server: https://kubernetes.default.svc  # Kubernetes server for deployment
  project: album-app  # Project to which the frontend application belongs
  source:
    path: frontend  # Directory containing frontend code/configuration
    repoURL: https://github.com/krishanthisera/album-app-config  # Git repository URL
    targetRevision: HEAD  # Target revision of the repository

If you follow the repo, the helm template creates the namespace and the ArgoCD project.

Note: If you want to ensure that child apps and all of their resources are deleted when the parent app is deleted, it's essential to add the appropriate finalizer to your Application definition. This finalizer action ensures proper cleanup and deletion of all related resources when the parent application is removed. See here

I have included all the ArgoCD applications this repo intended to deploy.

The frontend and backend ArgoCD Application resources point to their respective directory in the repository.

Frontend and Backend Helm Charts

These Helm charts define how the frontend and backend applications will be deployed on Kubernetes. They contain configuration details encapsulated within values.yaml. files.

replicaCount: 1
namespace: album-app
image:
  repository: ghcr.io/krishanthisera/album-app-backend
  pullPolicy: IfNotPresent
  tag: "v1.3.2" # Important: This tag signifies the version of the backend application.
  containerPort: 8080

service: 
  name: album-app-backend
  port: 8080

The value files are pretty straightforward. The only thing to note is the tag value. It is the image tag of the backend application.

During the release process of the application, the tag value will be replaced with the respective image tag.

Part 3 of the article series will cover the release process including CI/CD pipelines.

Stay tuned!