feat: argocd intro

dump/argo-cd/argo-cd.md

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+## Argo CD 
+
+### Problems with CI/CD 
+
+Jenkins/Gitlab CI flow:
+
+Build image -> Push image to registry -> Deploy to Kubernetes (using kubectl or helm)
+
+Challenges:
+
+- install and setup tools, like kubectl, helm, etc.
+- access to Kubernetes cluster
+- configure access to cloud platform, registry
+- security challenge (credentials to only particular part)
+- no visibility of deployment status 
+
+CD part can be improved by using Argo CD.
+
+### Argo CD 
+
+Argo CD is a declarative, GitOps continuous delivery tool for Kubernetes.
+
+- Part of the cluster 
+- ArgoCD pulls changes from Git repository and deploys them to Kubernetes cluster
+- Configuration is stored in Git repository (YAML files)
+- Separate repositories for environment, application, etc.
+- GitLab CI will update files in **separate** git repository
+- Separations of concerns, different roles can manage different repositories
+
+Commit image to repository <- ArgoCD detects changes -> Deploy to Kubernetes
+
+Supports:
+- k8s manifests
+- Helm charts
+- Kustomize
+
+### Benefits
+
+GitOps:
+
+- Common interface via Git and ArgoCD (all changes are visible)
+- All manual changes are overwritten by ArgoCD (model current + desired state)
+- Easy rollback (revert commit in Git)
+- Cluster disaster recovery (can create new cluster and point to Git repository) 
+
+k8s:
+
+- Access control with Git (without creating k8s users)
+- No external access for automation tools (Jenkins, Gitlab CI)
+- ArgoCD as k8s extension (etcd for storing data, k8s operator for managing resources using CRD)
+- One instance of ArgoCD can manage multiple clusters (also can one-to-one for environments via git branches or overlays in kustomize)
+
+Git (desired) -> ArgoCD (updating state) -> Kubernetes (current)
+
+https://argo-cd.readthedocs.io/en/stable/
+
+### Resources 
+
+- [TechWorld with Nana - ArgoCD Tutorial](https://youtu.be/MeU5_k9ssrs?si=ho7Dammwhjd9Ba1h)