Kubernetes Patterns, 2nd Edition

Chapter 6. Automated Placement

Automated Placement is the core function of the Kubernetes scheduler for assigning new Pods to nodes that match container resource requests and honor scheduling policies. This pattern describes the principles of the Kubernetes scheduling algorithm and how to influence the placement decisions from the outside.

Problem

A reasonably sized microservices-based system consists of tens or even hundreds of isolated processes. Containers and Pods do provide nice abstractions for packaging and deployment but do not solve the problem of placing these processes on suitable nodes. With a large and ever-growing number of microservices, assigning and placing them individually to nodes is not a manageable activity.

Containers have dependencies among themselves, dependencies to nodes, and resource demands, and all of that changes over time too. The resources available on a cluster also vary over time, through shrinking or extending the cluster or by having it consumed by already-placed containers. The way we place containers impacts the availability, performance, and capacity of the distributed systems as well. All of that makes scheduling containers to nodes a moving target.

Solution

In Kubernetes, assigning Pods to nodes is done by the scheduler. It is a part of Kubernetes that is highly configurable, and it is still evolving and improving. In this chapter, we cover the main scheduling control mechanisms, driving forces that affect the placement, why to choose ...