zRBasics

ArgoCD is a declarative gitops-based delviery tool for kubernetes. It continuously monitors the workloads and compares live state vs. stored state.

How does ArgoCD work?

• Uses git repos as the source of truth
• Supports kustomize, helm charts, etc.

Concepts and Terminology

• Application - a group of kubernetes resources as defined by a manifest
• ApplicationState:
  • Target State: the ‘stored’ state
  • Live State: the ‘live’ state

Features

• Auto deployment of apps to speficified target environments in multiple clusters
• Support for 3rd party templating tools such as kustomize, helm, etc.
• SSO Integration
• Multi-tenancy and RBAC policies for authorization
• Rollback/roll of applicatoins
• Health status analysis of apps
• Auatomated configuration drift dsetection and visualzation
• out of the box prometheus metrics
• audit trails
• webhook integration
• CLI and access tokens for automation and CI integration
• Web UI which provides real-time view of applications
• Automated or manual sync of apps to the desired state

ArgoCD Architecture

• Microservices architecture, there is no single “ArgoCD” component. Multiple distributed services working together
• Built on as many native kubernetes primitives as possible (controllers, CRDs, configmaps, secrets)

Components

• Application Controller / ApplicationSet Controller
  • Both are kubernetes operators (and therefore controllers)
  • Continuously watch Application / ApplicationSet resources and compare live state vs. desired state from the source repo
  • Also responsible for lifecycle events of the content they reconcile
• Repository Server
  • Keeps a local cache of the remote repo content
  • Generates the kubernetes manifests based on:
    • repo type
    • repo location
    • path within the repo
    • template tool parameters (helm, kustomize, etc.)
  • Custom plugins run here too since they influence manifest generation
• API Server
  • gRPC/REST server
  • Handles:
    • Application management and status reporting
    • Operations: sync, rollback, user defined actions
    • Cluster and repo management
    • RBAC enforcement
  • The UI, CLI and external CI/CD systems all depend on this
  • Also serves the web UI
• Redis
  • In-memory cache. Caches repo contents, k8s resource state, and connection status of repos/clusters
  • NOT persisted, always rebuilt at startup
• CLI (argocd)
  • Talks to the API. Superset of what the UI can do
• SSO
  • Local users or external users
  • OIDC supported directly
  • Dex is bundled for identity providers that don’t speak OIDC (acts as a bridge)
• Notifications
  • Included by default since 2.3
  • Triggers + templates based on application lifecycle events
  • Slack, email, webhooks, etc.

Custom Resources

Every install includes 3 CRDs:

• Application
• AppProject
• ApplicationSet

These CRDs are effectively your interface for managing your cluster(s).

Key Themes

• Declarative: everything (including argo’s own config in ConfigMaps/Secrets) is declarative. This means ArgoCD can manage itself via GitOps
• Stateless: config is the state, can be rebuilt at any time
  • etcd is the persistent store
  • If state needs to be tracked against a resource, use the status field
  • Redis is only a volatile cache
• **FlexiblezR: multiple repo types, built in support for Kustomize, Helm, Jsonnet, and user defined tools