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Topograph with Kubernetes

Topograph is a tool designed to enhance scheduling decisions in Kubernetes clusters by leveraging network topology information.

Overview

Topograph's primary objective is to assist the Kubernetes scheduler in making intelligent pod placement decisions based on the cluster's network topology. It achieves this by:

  1. Interacting with Cloud Service Providers (CSPs)
  2. Extracting cluster topology information
  3. Updating the Kubernetes environment with this topology data

Current Functionality

Topograph performs the following key actions:

  1. ConfigMap Creation: Generates a ConfigMap containing topology information. This ConfigMap is not currently utilized but serves as an example for potential future integration with the scheduler or other systems.

  2. Node Labeling: Applies labels to nodes that define their position within the cloud topology. For example, if a node connects to switch S1, which connects to switch S2, and then to switch S3, Topograph will apply the following labels to the node:

    topology.kubernetes.io/network-level-1: S1
topology.kubernetes.io/network-level-2: S2
topology.kubernetes.io/network-level-3: S3

Use of Topograph

While there is currently no fully network-aware scheduler capable of optimally placing groups of pods based on network considerations, Topograph serves as a stepping stone toward developing such a scheduler.

Topograph can be used in conjunction with Kubernetes' existing PodAffinity feature. This combination enhances pod distribution based on network topology information.

The following excerpt describes a Kubernetes object specification for a cluster with a three-tier network switch hierarchy. The goal is to improve inter-pod communication by assigning pods to nodes within closer network proximity.

    affinity:
      podAffinity:
        preferredDuringSchedulingIgnoredDuringExecution:
          - weight: 70
            podAffinityTerm:
              labelSelector:
                matchExpressions:
                  - key: app
                    operator: In
                    values:
                      - myapp
              topologyKey: topology.kubernetes.io/network-level-2
          - weight: 90
            podAffinityTerm:
              labelSelector:
                matchExpressions:
                  - key: app
                    operator: In
                    values:
                      - myapp
              topologyKey: topology.kubernetes.io/network-level-1

Pods are prioritized to be placed on nodes sharing the label topology.kubernetes.io/network-level-1. These nodes are connected to the same network switch, ensuring the lowest latency for communication.

Nodes with the label topology.kubernetes.io/network-level-2 are next in priority. Pods on these nodes will still be relatively close, but with slightly higher latency.

In the three-tier network, all nodes will share the same topology.kubernetes.io/network-level-3 label, so it doesn’t need to be included in pod affinity settings.

Since the default Kubernetes scheduler places one pod at a time, the placement may vary depending on where the first pod is placed. As a result, each scheduling decision might not be globally optimal. However, by aligning pod placement with network-aware labels, we can significantly improve inter-pod communication efficiency within the limitations of the scheduler.

Configuration and Deployment

TBD

Validation and Testing

TBD