Argo CD it self can not build Image , need ArgoCD updater or Jenkins, or other CI tool - unix1998/technical_notes GitHub Wiki

The description that ArgoCD can detect source code changes and directly trigger a new deployment is somewhat misleading. ArgoCD itself doesn't directly monitor source code repositories for changes nor does it build container images from source code. Here's a clarification on how ArgoCD operates and how it integrates with CI/CD pipelines:

How ArgoCD Works

GitOps Principles:
- ArgoCD follows GitOps principles, where the desired state of the Kubernetes clusters is defined declaratively in Git repositories. This includes the Kubernetes manifests (YAML files) that define the deployment configurations.
Monitoring Git Repositories:
- ArgoCD continuously monitors the specified Git repositories for changes to these Kubernetes manifests. When a change is detected in the repository (e.g., a new commit that updates a deployment YAML file), ArgoCD synchronizes the cluster state with the desired state defined in Git.
Deployment Synchronization:
- ArgoCD synchronizes the cluster by applying the updated Kubernetes manifests to the cluster, ensuring that the deployed resources match the desired state specified in Git.

Integration with CI Pipelines

To detect source code changes and trigger new deployments, ArgoCD is typically used in conjunction with Continuous Integration (CI) tools. Here's how the process usually works:

Source Code Change:
- A developer makes a change to the source code and commits it to the source code repository (e.g., GitHub, GitLab).
CI Pipeline:
- A CI pipeline (e.g., Jenkins, GitLab CI, GitHub Actions) is triggered by the commit. The CI pipeline is responsible for building the new container image and pushing it to a container registry (e.g., Docker Hub, AWS ECR).
Update Kubernetes Manifests:
- After the new image is built and pushed to the registry, the CI pipeline updates the Kubernetes manifests in the GitOps repository to reference the new image tag. This could be an automated step in the CI pipeline.
ArgoCD Synchronization:
- ArgoCD detects the change in the GitOps repository (the updated image tag in the Kubernetes manifest) and synchronizes the cluster state to match the new desired state. This results in the deployment of the new container image to the cluster.

Example Workflow

Here's an example of how this workflow might look in practice:

Commit and Push Code:
- A developer commits code changes to the repository:
```
git commit -am "Update application logic"
git push
```

CI Pipeline Triggered:

The CI pipeline is triggered by the commit. It builds the new Docker image and pushes it to the container registry:

# Example CI pipeline (e.g., GitLab CI)
stages:
  - build
  - deploy

build_image:
  stage: build
  script:
    - docker build -t myapp:latest .
    - docker tag myapp:latest registry.example.com/myapp:latest
    - docker push registry.example.com/myapp:latest

update_manifests:
  stage: deploy
  script:
    - sed -i 's|image: registry.example.com/myapp:.*|image: registry.example.com/myapp:latest|' k8s/deployment.yaml
    - git add k8s/deployment.yaml
    - git commit -m "Update deployment to use new image"
    - git push

ArgoCD Sync:
- ArgoCD detects the change in the k8s/deployment.yaml file and synchronizes the cluster state with the updated manifests, deploying the new image.

Summary

ArgoCD monitors Git repositories for changes in Kubernetes manifests and synchronizes the cluster state accordingly.
CI Tools handle the detection of source code changes, building new container images, and updating Kubernetes manifests in the GitOps repository.
Integration between CI pipelines and ArgoCD enables a seamless deployment process following GitOps principles, ensuring that source code changes result in updated deployments after images are built and manifests are updated.

By leveraging both ArgoCD and CI tools, you can achieve a robust and automated CI/CD pipeline that adheres to GitOps practices.