Usage Thresholds

Introduction

The Dynamic Traffic Controller allows you to set two thresholds to mark the point at which the weight should begin to decrease from 100 and the point at which the weight should be 1. The Dynamic Traffic Controller will then calculate the weight based on the current usage value and the two thresholds.

note

A weight of 0 means do not send traffic to this service and is reserved for failure conditions.

Let us imagine that we have our two thresholds at 60 and 90. If we have a current usage of 60%, the weight will remain at 100. If we have a current usage of 70%, the weight will be 67. If we have a current usage of 90%, the weight will be 1.

If we have thresholds of 50 and 80 with a usage of 65%, the weight will be 50.

The weight is calculated as follows:

weight = 100 - [(current usage - low-threshold) / (high-threshold - low-threshold) * 100]

Configuration

To enable threshold on a service, add the following annotation to the relevant service definition.

annotations:
  external-dns.alpha.kubernetes.io/usage-thresholds: LOW_INT,HIGH_INT

Example:

annotations:
  external-dns.alpha.kubernetes.io/usage-thresholds: 50,80

The following example shows the annotations added to our sample service definition from the onboarding document.

apiVersion: v1
kind: Service
metadata:
  annotations:
    external-dns.alpha.kubernetes.io/usage-thresholds: 50,80
    external-dns.alpha.kubernetes.io/hostname: myapp.example.com
    external-dns.alpha.kubernetes.io/ttl: "60"
    external-dns.alpha.kubernetes.io/weight: "100"
  labels:
    app: nginx
    avesha.dns.metrics.io/monitor: "true"
  name: myapp-internal-service
  namespace: kubeslice-system
spec:
  externalTrafficPolicy: Cluster
  ipFamilyPolicy: SingleStack
  ports:
  - name: http
    nodePort: 31569
    port: 80
    protocol: TCP
    targetPort: 80
  selector:
    app: nginx
  sessionAffinity: None
  type: LoadBalancer

Confirm Measurement

After the thresholds are added, the service is influenced by the above equation. You can confirm the DTC has picked up the service by viewing the logs for the dns-controller pod. You can use a command similar to the one below, but with your unique pod name.

kubectl logs dns-controller-5f7b7f7f9f-5j2xg -n kubeslice-system