Control Plane Components¶
What is the Control Plane?¶
The Control Plane is the brain of Kubernetes.
It is responsible for:
- Making scheduling decisions
- Maintaining cluster state
- Responding to changes
Core Components¶
API Server¶
The API Server is the front door to Kubernetes.
- All communication goes through it
- Validates and processes requests
- Persists state to etcd
etcd¶
A distributed key-value store.
- Stores all cluster data
- Acts as the source of truth
- Highly consistent and fault-tolerant
Scheduler¶
Assigns workloads to nodes.
- Watches for unscheduled Pods
- Selects the best node based on:
- Resources
- Constraints
- Policies
Controller Manager¶
Runs controllers that maintain system state.
Examples:
- Node Controller
- Deployment Controller
- ReplicaSet Controller
Each controller follows:
Desired State → Compare → Act
How They Work Together¶
graph TD
User --> APIServer
APIServer --> etcd
APIServer --> Scheduler
APIServer --> ControllerManager
Scheduler --> Node
ControllerManager --> APIServer
Real-World Implications¶
- API Server downtime = cluster unusable
- etcd corruption = cluster state loss
- Controllers are what make Kubernetes "self-healing"
Key Takeaways¶
- Everything flows through the API Server
- etcd is the single source of truth
- Controllers enforce desired state continuously