The descheduler module ensures operation of Descheduler in Deckhouse Kubernetes Platform (DKP).
The module analyzes the cluster state periodically and evicts pods that match conditions defined in active strategies. Evicted pods are then scheduled again according to the current cluster state. This helps redistribute workloads in line with the selected strategy.
If the Metrics API service is registered in the cluster, the module uses it to obtain information about the current resource consumption.
Strategy parameters are configured using the Descheduler custom resource. A module hook processes these resources and recreates configuration for Descheduler.
Module architecture
The following simplifications are made in the diagram:
- The diagram shows containers in different pods interacting directly with each other. In reality, they communicate via the corresponding Kubernetes Services (internal load balancers). Service names are omitted if they are obvious from the diagram context. Otherwise, the Service name is shown above the arrow.
- Pods may run multiple replicas. However, each pod is shown as a single replica in the diagram.
The Level 2 C4 architecture of the descheduler module and its interactions with other DKP components are shown in the following diagram:
Module components
The descheduler module consists of a single descheduler component that includes the following containers:
- descheduler: Main container.
- kube-rbac-proxy: Sidecar container with a Kubernetes RBAC-based authorization proxy that provides secure access to descheduler metrics.
Module interactions
The module interacts with the kube-apiserver component:
- Watches standard Node and Pod resources.
- Retrieves current resource consumption through the Metrics API.
- Evicts running pods to match active strategies.
- Authorizes requests for metrics.
The prometheus component interacts with the module by collecting module metrics.