Onboard a Service with DTC

Introduction

Assuming your service is already being advertised by ExternalDNS, enabling weight management using the Dynamic Traffic Controller (DTC) is as easy as adding a label to the service.

note

This guide assumes you have already deployed ExternalDNS and have added ExternalDNS annotations for advertisement to your provider. If this is not true, see Getting Started with ExternalDNS.

Add the Label

The following code is an excerpt from a Service definition with ExternalDNS annotations already applied.

apiVersion: v1
kind: Service
metadata:
  annotations:
    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
  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

To enable weight management, add the avesha.dns.metrics.io/monitor: "true" label as shown on the line below app: nginx.

apiVersion: v1
kind: Service
metadata:
  annotations:
    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 label is added, the service will be monitored by DTC. 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

You can watch for a few minutes as the Dynamic Traffic Controller collects historical usage values and calculates a moving average. An example of what this may look like is below.

{"level":"info","ts":"2022-09-09T20:08:26.801601081Z","msg":"Average history","service":"frontend-external","average":91,"history":"[ 91, 91, 91, 91, ]"}
{"level":"info","ts":"2022-09-09T20:08:26.80165393Z","msg":"Service: frontend-external, CPU Usage: 17.0 mCPU (8.5%), CPU Limits: 200.0 mCPU"}
{"level":"info","ts":"2022-09-09T20:08:26.801662125Z","msg":"Service: frontend-external, Current Weight: 91, Previous: 92, Not Significant, Only Updating Usage..."}
{"level":"info","ts":"2022-09-09T20:08:57.618496037Z","msg":"Average history","service":"frontend-external","average":91,"history":"[ 91, 91, 91, 91, 90, ]"}
{"level":"info","ts":"2022-09-09T20:08:57.618550069Z","msg":"Service: frontend-external, CPU Usage: 20.1 mCPU (10.1%), CPU Limits: 200.0 mCPU"}
{"level":"info","ts":"2022-09-09T20:08:57.618564776Z","msg":"Service: frontend-external, Current Weight: 91, Previous: 92, Not Significant, Only Updating Usage..."}
{"level":"info","ts":"2022-09-09T20:09:28.70038254Z","msg":"Average history","service":"frontend-external","average":91,"history":"[ 91, 91, 91, 91, 90, 90, ]"}
{"level":"info","ts":"2022-09-09T20:09:28.700446358Z","msg":"Service: frontend-external, CPU Usage: 20.1 mCPU (10.1%), CPU Limits: 200.0 mCPU"}
{"level":"info","ts":"2022-09-09T20:09:28.700454594Z","msg":"Service: frontend-external, Current Weight: 91, Previous: 92, Not Significant, Only Updating Usage..."}