Resource Requests, Limits and QoS Classes

Configuration and Secrets / Guide 35 of 103 / Intermediate

• Kubernetes1.36.4
• Cluster4 nodes
• Runtimecontainerd 2.2.6
• CNICalico v3.32.1
• TimeAbout 30 min

Node utilisation figures are whatever your cluster is doing at the time. The QoS assignments and the OOM behaviour are deterministic.

• metrics-serverinstalled

This guide includes

Use this when you have to decide what goes in requests and what goes in limits. This matters because they do completely different jobs - one reserves capacity at scheduling time, the other is enforced at runtime - and together they silently decide which Pod is evicted first.

• telling a reservation from a ceiling, and seeing where each one is enforced
• reading the QoS class Kubernetes derived that you never wrote - Guaranteed, Burstable, BestEffort
• comparing what the scheduler reserved with what the node is actually using
• giving a container a 64Mi limit, asking it to write 200Mi, and reading the OOMKilled reason back

Before you start

• A working cluster and kubectl.
• The Pods guide. Requests and limits are fields on a container, so that is the shape you need.
• metrics-server if you want kubectl top to work. It is not required for anything else here.

1. 1

   Two numbers that do completely different jobs

2. 2

   The class you never wrote

3. 3

   What the scheduler actually reserved

4. 4

   A memory limit is not advice

5. 5

   Clean up

Official sources

• Resource management for pods and containers
• Pod Quality of Service classes
• Node-pressure eviction
• LimitRange