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Worker Nodes

  • These nodes do the actual work (need more resources)
  • Each worker node has multiple pods running on it.
  • 3 processes must be installed on every worker node
    • Container Runtime (eg. docker)
    • Kubelet
      • process of Kubernetes
      • starts pods and runs containers inside them
      • allocates resources from the node to the container
    • Kubeproxy
      • process of Kubernetes
      • forwards the requests to pods intelligently
      • Image
        • Kubeproxy forwards requests to the DB pod running on the same node to minimize network overhead.
        • attachments/Pasted image 20220828123915.jpg

Master Nodes

  • Control the cluster state & manage worker nodes
  • Need less resources as they don't do the actual work
  • Usually multi-master for fault tolerance
  • 4 processes run on every master node
    • API Server
      • User interacts with the cluster via the API server using a client (Kubernetes Dashboard, CLI, or Kubernetes API)
      • Cluster gateway (acts as the entry point into the cluster)
      • Can be used for authentication
      • Image
        • attachments/Pasted image 20220828124843.jpg
    • Scheduler
      • Decides the node where the new pod should be scheduled and sends a request to the Kubelet to start a pod.
      • Image
        • attachments/Pasted image 20220828125230.jpg
    • Controller Manager
      • Detects state changes like crashing of pods
      • If a pod dies, it requests scheduler to schedule starting up of a new pod
      • Image
        • attachments/Pasted image 20220828125455.jpg
    • etcd
      • Key-value store of the cluster state (also known as cluster brain)
      • Cluster changes get stored in the etcd
      • In multi-master configuration, etcd is a distributed key-value store
      • Application data is not stored in the etcd


  • A collection of nodes grouped together (if one node goes down, the application can still continue to run)
  • In a K8 cluster, master or worker nodes can be added dynamically

Layers of Abstraction

  • Deployment (manages replicasets)
  • Replicaset (how many replicas of pods to create)
  • Pod
  • Container
Everything below the Deployment layer is managed by Kubernetes

Last updated: 2022-10-08