Limiting CPU & Memory

As a short description:

• CPU Requests are limits that are applied when there is CPU congestion, and as such can burst above their set limits.
• CPU Limits are hard limits on how much CPU time the particular container gets access to.

This is useful for game servers, not just as a mechanism to distribute compute resources evenly, but also as a way to advice the Kubernetes scheduler how many game server processes it is able to fit into a given node in the cluster.

It’s worth reading the Managing Compute Resources for Containers Kubernetes documentation for more details on “requests” and “limits” to both CPU and Memory, and how to configure them.

GameServers

Since the GameServer specification provides a full PodSpecTemplate, we can take advantage of both resource limits and requests in our GameServer configurations.

For example, to set a CPU limit on our GameServer configuration of 250m/0.25 of a CPU, we could do so as followed:

apiVersion: "agones.dev/v1"
kind: GameServer
metadata:
  name: "simple-game-server"
spec:
  ports:
  - name: default
    containerPort: 7654
  template:
    spec:
      containers:
      - name: simple-game-server
        image: us-docker.pkg.dev/agones-images/examples/simple-game-server:0.35
        resources:
          limits:
            cpu: "250m" #this is our limit here

If you do not set a limit or request, the default is set by Kubernetes at a 100m CPU request.

SDK GameServer sidecar

You may also want to tweak the CPU request or limits on the SDK GameServer sidecar process that spins up alongside each game server container.

You can do this through the Helm configuration when installing Agones.

By default, this is set to having a CPU request value of 30m, with no hard CPU limit. This ensures that the sidecar always has enough CPU to function, but it is configurable in case a lower, or higher value is required on your clusters, or if you desire hard limit.