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node-labeler.md

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Node-Labeler Component

Overview

The Node-Labeler component in Gitpod is a Kubernetes controller responsible for managing node labels and annotations that are required for workspaces to run properly. It monitors the status of critical services like registry-facade and ws-daemon on each node, and adds or removes labels accordingly. Additionally, it manages cluster-autoscaler annotations to prevent nodes with active workspaces from being scaled down.

Purpose

The primary purposes of the Node-Labeler component are:

  • Ensure workspaces are scheduled only on nodes with required services
  • Add and remove node labels based on service availability
  • Prevent cluster-autoscaler from removing nodes with active workspaces
  • Enable efficient node utilization in Kubernetes clusters
  • Facilitate proper workspace scheduling
  • Monitor the health of critical workspace services
  • Support the Gitpod workspace infrastructure
  • Optimize cluster resource usage
  • Provide metrics for service readiness

Architecture

The Node-Labeler component consists of several key parts:

  1. Pod Reconciler: Watches pods of critical services and updates node labels
  2. Node Scaledown Annotation Controller: Manages cluster-autoscaler annotations based on workspace presence
  3. Health Checks: Verifies service availability before adding labels
  4. Metrics Collection: Tracks service readiness times and counts

The component operates as a Kubernetes controller with leader election, ensuring only one instance is active at a time. It uses the controller-runtime library to watch for changes to pods and workspaces, and reconciles the state of node labels and annotations accordingly.

Key Features

Node Labeling

  • Service Readiness Labels: Adds labels to nodes when critical services are ready
  • Label Removal: Removes labels when services are no longer available
  • Health Verification: Checks TCP connectivity and service health before adding labels
  • Registry-Facade Verification: Performs specific checks for registry-facade readiness
  • Automatic Reconciliation: Periodically reconciles node labels to ensure correctness

Cluster-Autoscaler Integration

  • Scale-down Prevention: Adds annotations to prevent cluster-autoscaler from removing nodes with active workspaces
  • Workspace Tracking: Monitors workspace presence on nodes
  • Annotation Management: Adds or removes cluster-autoscaler.kubernetes.io/scale-down-disabled annotation
  • Periodic Reconciliation: Regularly checks all nodes to ensure annotations are correct
  • Event-based Updates: Responds to workspace creation, deletion, and node changes

Monitoring and Metrics

  • Service Readiness Metrics: Tracks how long it takes for services to become ready
  • Service Count Metrics: Counts the number of service instances
  • Health Endpoints: Provides health and readiness endpoints
  • Logging: Detailed logging of label and annotation changes

Configuration

The Node-Labeler component can be configured through command-line flags:

General Configuration

  • --json-log, -j: Produce JSON log output (default: true)
  • --verbose, -v: Enable verbose logging
  • --namespace: Namespace where Gitpod components are running (default: default)

Service Configuration

  • --registry-facade-port: Port for registry-facade node port (default: 31750)
  • --ws-daemon-port: Port for ws-daemon service (default: 8080)

Integration Points

The Node-Labeler component integrates with:

  1. Kubernetes API: For managing node labels and annotations
  2. Registry-Facade: Checks readiness of registry-facade service
  3. WS-Daemon: Checks readiness of ws-daemon service
  4. Cluster-Autoscaler: Prevents scale-down of nodes with active workspaces
  5. Workspace Controller: Monitors workspace placement on nodes

Usage Patterns

Node Label Management

The component adds the following labels to nodes:

  • gitpod.io/registry-facade_ready_ns_<namespace>: Indicates registry-facade is ready
  • gitpod.io/ws-daemon_ready_ns_<namespace>: Indicates ws-daemon is ready

These labels are used by the workspace scheduler to ensure workspaces are only scheduled on nodes with the required services.

Cluster-Autoscaler Annotation Management

The component adds or removes the following annotation:

  • cluster-autoscaler.kubernetes.io/scale-down-disabled: Prevents cluster-autoscaler from removing nodes with active workspaces

Dependencies

Internal Dependencies

  • components/common-go: Common Go utilities
  • components/ws-manager-api/go: Workspace manager API
  • components/ws-manager-mk2: Workspace manager CRDs

External Dependencies

  • Kubernetes controller-runtime: For building Kubernetes controllers
  • Kubernetes client-go: For interacting with the Kubernetes API
  • Prometheus metrics: For exposing metrics

Security Considerations

The component implements several security measures:

  1. Least Privilege: Requires only the necessary permissions to manage node labels and annotations
  2. Leader Election: Ensures only one instance is active at a time
  3. Namespace Isolation: Can be configured to watch only specific namespaces
  4. TLS Verification: Supports TLS for secure communication with services
  5. Error Handling: Proper handling of errors to prevent security issues

Implementation Details

Pod Reconciler

The Pod Reconciler watches for changes to pods with the component label matching "ws-daemon" or "registry-facade". When a pod becomes ready, it:

  1. Checks if the pod is running on a node
  2. Verifies TCP connectivity to the service
  3. For registry-facade, performs additional HTTP health checks
  4. Adds the appropriate label to the node if all checks pass
  5. Removes the label when the pod is deleted or becomes not ready

Node Scaledown Annotation Controller

The Node Scaledown Annotation Controller watches for changes to workspaces. When a workspace is created, deleted, or moved to a different node, it:

  1. Counts the number of workspaces on the affected node
  2. Adds the cluster-autoscaler.kubernetes.io/scale-down-disabled annotation if there are workspaces on the node
  3. Removes the annotation if there are no workspaces on the node
  4. Periodically reconciles all nodes to ensure annotations are correct

Related Components

  • WS-Manager-MK2: Uses the node labels for workspace scheduling
  • Registry-Facade: Provides container images for workspaces
  • WS-Daemon: Provides workspace services on nodes
  • Cluster-Autoscaler: Uses annotations to determine which nodes can be scaled down