Kubernates notes k8s controller - replication controller

Replication Controller vs ReplicaSet in Kubernetes

Both ReplicationController (RC) and ReplicaSet (RS) ensure that a specified number of pod replicas are running at any given time, but ReplicaSet is the newer and more flexible version of ReplicationController.

1. Replication Controller (RC)

🔹 Purpose: Ensures a specified number of identical pods are running.
🔹 Key Features:

• Watches running pods and replaces failed ones.
• Uses equality-based selectors (matchLabels).
• Legacy feature; replaced by ReplicaSet in modern Kubernetes.

💡 Use Case: Basic pod scaling in older Kubernetes versions.

2. ReplicaSet (RS)

🔹 Purpose: Enhanced version of ReplicationController, supporting more flexible pod selection.

🔹 Key Features:

• Uses label selectors (supports matchExpressions along with matchLabels).
• Works with Deployments, making pod management easier.
• Supports rolling updates when combined with Deployments.

💡 Use Case: Used in modern Kubernetes for pod scaling and high availability. Usually not used directly Deployments manage ReplicaSets internally.

Command to scale replicas

kubectl scale --replicas=6 -f replicaset-defination.yml