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kubernetesgoogle-kubernetes-engine

What is the relation between nodes, pods, containers? How app is replicated in cluster?

I am new to kubernetes and I went through many articles but didnt find a basic answer to my doubt.

Suppose I have 2 nodes kubernete cluster and I have deployed 2 applications on it then.

  1. My both of the apps will be hosted on both of the nodes? Like app1 on both of the nodes and similarly app2? it means we have replication factor of 2 by default. Correct?

  2. It will have 1 pod per node? What will be the structure?

Node 1, Pod1 - > App1
Node 1, Pod1 - > App2
Node 2, Pod1 - > App1
Node 2, Pod1 - > App2
  1. If I have set replication factor=2 then how it will affect the structure? Will it create 
Node 1- Pod1 - > App1
Node 1- Pod2 - > App2
Node 2- Pod1 - > App1
Node 2- Pod2 - > App2
  1. What is deployment in terms of above physical/logical structures? How it differs with service? Deployment is specific to per node?
Solution

  • There's no predefined tying of pods to nodes. The Kubernetes scheduler dynamically decides which node to assign a pod to when the pod is created.

    In general, a Kubernetes app consists of a set of replicated pods (in most cases managed by a Deployment resource). Which nodes these pods end up running on is up to the scheduler. There's no built-in policy that replica pods of the same app must run on different nodes.

    However, you can influence the decision of the scheduler with various mechanisms: