Halyard

Halyard is a tool for horizontal autoscaling with Kubernetes (K8S). It leverages a metrics backend to determine the current value of a metric, and linearly scales the number of pods so the metric approaches a given target value. This enables dynamic scaling in response to changes in load.

Backends

Currently supported backends:

• Prometheus

Running in Docker

1. docker run -d -v Config.json:/config/Config.json:ro patientcoeng/halyard

Running in Kubernetes

1. curl -o deployment.yaml https://raw.githubusercontent.com/patientcoeng/halyard/master/manifests/deployment.yaml
2. Edit deployment.yaml to replace the placeholder values with those specific to your setup
3. kubectl apply -f deployment.yaml

Building from Source

1. Clone the halyard repository
2. Install govendor "go install github.com/kardianos/govendor"
3. Run "govendor sync"
4. Run "go build"
5. Run halyard

Configuration

Halyard expects a JSON-encoded configuration file to be present in the same directory as the Halyard binary. You can use the config command line option to use a different file. An example file is listed below, for reference:

{
  "period": 30,
  "namespace": "default",
  "backendEndpoints": {
    "prometheus": "https://my-prometheus-server"
  },
  "alertConfig": {
      "slack": {
        "webhookURL": "https://hooks.slack.com/services/YOUR_SERVICE_ID",
        "channel": "#yourchannel"
      }
  }
}

Deployment Annotations

Halyard works by reading annotations on Kubernetes. The following annotations are supported. All values are strings.

• halyard.patientco.com/query
  • A query string, recognized by the designated backend
• halyard.patientco.com/backend
  • The name of the backend to process the given query
• halyard.patientco.com/target-value
  • The target value to set the query result to, as a string.
• halyard.patientco.com/min-replicas
  • The minimum number of allowed replicas
• halyard.patientco.com/max-replicas
  • The maximum number of allowed replicas
• halyard.patientco.com/scaling-policy
  • Currently only "linear" is supported

CLI Options

-config string
    Location of JSON-encoded config file (default "Config.json")