Call endpoint from Kubernetes Cron Job

Question

I have a web app running in a docker container on kubernetes cluster. The app has an endpoint which I want it to be called periodically. The problem is, this app is running on multiple nodes and I want only one specific node to perform that task. Is that possible? If yes, how?

Answer 1

CronJobs are a good choice. Here's a quick layout that runs 3 nginx pods accepting all traffic. Every minute, a Job curls 1 of the 3 pods (always the same pod).

apiVersion: apps/v1beta1
kind: Deployment
metadata:
  name: main
  labels:
    app: nginx
spec:
  replicas: 2
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.7.9
        ports:        - containerPort: 80
---apiVersion: apps/v1beta1
kind: Deployment
metadata:
  name: singleton
  labels:
    app: nginx
    special: singleton
spec:
  replicas: 1
  selector:
    matchLabels:
      app: nginx
      special: singleton
  template:
    metadata:
      labels:
        app: nginx
        special: singleton
    spec:
      containers:
      - name: nginx
        image: nginx:1.7.9
        ports:
        - containerPort: 80
--
kind: Service
apiVersion: v1
metadata:
  name: allpods
spec:
  selector:
    app: nginx
  ports:
  - protocol: TCP
    port: 80
    targetPort: 80
--
kind: Service
apiVersion: v1
metadata:
  name: singleton
spec:
  selector:
    special: singleton
  ports:
 - protocol: TCP
    port: 80
    targetPort: 80
---
piVersion: batch/v1beta1
kind: CronJob
metadata:
  name: callout
spec:
  schedule: "*/1 * * * *"
  concurrencyPolicy: Forbid
  successfulJobsHistoryLimit: 1
  failedJobsHistoryLimit: 1
  jobTemplate:
    spec:
      template:
        spec:
          containers:
          - name: callout
            image: buildpack-deps:curl
            args:
            - /bin/sh
            - -ec
            - curl http://singleton
          restartPolicy: Never