Resource Management (Requests vs. Limits)

How Kubernetes manages CPU and Memory for containers.

Edit Concept ✏️

Kubernetes Resource Management

Kubernetes allows you to specify how much CPU and Memory (RAM) each container needs. This is critical for the scheduler to decide which node to place a Pod on and for the node to manage its resources.

1. Requests

  • Definition: The minimum amount of resources a container is guaranteed to have.
  • Scheduling: The scheduler uses the sum of requests to ensure a node has enough capacity before placing a Pod there.
  • Over-commitment: If a node is over-committed, containers are guaranteed their requested amount but may compete for any remaining “slack” capacity.

2. Limits

  • Definition: The maximum amount of resources a container is allowed to consume.
  • CPU Limits: If a container exceeds its CPU limit, it is throttled (slowed down). It is usually not killed.
  • Memory Limits: If a container exceeds its memory limit, it is OOM Killed (Out of Memory) by the kernel.

3. Quality of Service (QoS) Classes

Kubernetes assigns a QoS class to Pods based on their requests and limits:

  • Guaranteed: Requests and Limits are equal for all containers in the Pod. (Most stable).
  • Burstable: At least one container has a request, but they are not equal to limits.
  • BestEffort: No requests or limits are specified. (First to be killed when the node is under pressure).