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Scheduling function runs

Cron Connector

The cron-connector is an OpenFaaS event-connector which can be used to trigger functions on a timed-basis. It makes use of the OpenFaaS REST API, so it is capable of working with all OpenFaaS Providers.

Kubernetes

  • Deploy the connector
arkade install cron-connector
  • Now annotate a function with a topic of cron-function and a schedule using a valid CRON expression:

# (Abridged YAML)

functions:
  nodeinfo:
    image: functions/nodeinfo
    skip_build: true
    annotations:
      topic: cron-function
      schedule: "*/5 * * * *"
nodeinfo.yaml

faas-cli deploy -f nodeinfo.yaml
  • Or deploy directly from the store
faas-cli store deploy nodeinfo \
  --annotation topic="cron-function" \
  --annotation schedule="*/5 * * * *"
  • Now check the logs
kubectl logs -n openfaas-fn deploy/nodeinfo -f

You'll see the function invoked every 5 minutes as per the schedule.

To stop the invocations, remove the two annotations or remove the cron-connector deployment.

If you would like to explore how to write CRON expressions, then see https://crontab.guru/

faasd

faasd also supports the cron-connector.

See Serverless For Everyone Else for detailed instructions on configuration and usage.

The Kubernetes CronJob

Kubernetes has its own CronJob API resource, which cam be used to schedule regularly function executions with a cron expression.

We assume that you have used the recommended install of faas-netes which means that you have OpenFaaS deployed into two namespaces:

  1. openfaas for the core components
  2. openfaas-fn for the function deployments

Simple CronJob

For this example we'll deploy a function which can print system info about the container it's running in:

faas-cli store deploy nodeinfo

We can then define a Kubernetes CronJob to call this function every minute using this manifest file:

# node-cron.yaml
apiVersion: batch/v1beta1
kind: CronJob
metadata:
  name: nodeinfo
  namespace: openfaas
spec:
  schedule: "*/1 * * * *"
  concurrencyPolicy: Forbid
  successfulJobsHistoryLimit: 1
  failedJobsHistoryLimit: 3
  jobTemplate:
    spec:
      template:
        spec:
          containers:
          - name: openfaas-cli
            image: ghcr.io/openfaas/faas-cli:latest
            imagePullPolicy: IfNotPresent
            command:
            - /bin/sh
            args:
            - -c
            - echo "verbose" | faas-cli invoke nodeinfo -g http://gateway.openfaas:8080
          restartPolicy: OnFailure

You should also update the image to the latest version of the faas-cli available found via the GitHub Container Registry or faas-cli releases page.

The important thing to notice is that we are using a Docker container with the faas-cli to invoke the function. This keeps the job very generic.

We schedule the job by applying our manifest

$ kubectl apply -f node-cron.yaml

$ kubectl -n=openfaas get cronjob nodeinfo --watch
NAME       SCHEDULE      SUSPEND   ACTIVE    LAST SCHEDULE   AGE
nodeinfo   */1 * * * *   False     0         <none>          42s
nodeinfo   */1 * * * *   False     1         2s        44s
nodeinfo   */1 * * * *   False     0         12s       54s
nodeinfo   */1 * * * *   False     1         2s        1m
nodeinfo   */1 * * * *   False     0         12s       1m

Unfortunately, there is no one-line command in kubectl for getting the logs from a cron job. Kubernetes creates new Job objects for each run of the CronJob, so we can look up that last run of our CronJob using

$ kubectl -n openfaas get job
NAME                  DESIRED   SUCCESSFUL   AGE
nodeinfo-1529226900   1         1            6s

We can use this to then get the output logs

$ kubectl -n openfaas logs -l "job-name=nodeinfo-1529226900"
Hostname: nodeinfo-6fffdb4446-57mzn

Platform: linux
Arch: x64
CPU count: 1
Uptime: 997420
[ { model: 'Intel(R) Xeon(R) CPU @ 2.20GHz',
    speed: 2199,
    times:
     { user: 360061300,
       nice: 2053900,
       sys: 142472900,
       idle: 9425509300,
       irq: 0 } } ]
{ lo:
   [ { address: '127.0.0.1',
       netmask: '255.0.0.0',
       family: 'IPv4',
       mac: '00:00:00:00:00:00',
       internal: true },
     { address: '::1',
       netmask: 'ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff',
       family: 'IPv6',
       mac: '00:00:00:00:00:00',
       scopeid: 0,
       internal: true } ],
  eth0:
   [ { address: '10.4.2.40',
       netmask: '255.255.255.0',
       family: 'IPv4',
       mac: '0a:58:0a:04:02:28',
       internal: false },
     { address: 'fe80::f08e:d8ff:fecc:9635',
       netmask: 'ffff:ffff:ffff:ffff::',
       family: 'IPv6',
       mac: '0a:58:0a:04:02:28',
       scopeid: 3,
       internal: false } ] }

This example assumes no authentication is enabled on the gateway.

Multiple Namespaces

In this example, I created the CronJob in the same namespace as the gateway. If we deploy the CronJob in a different namespace, then we need to update the job arguments to accommodate. Fortunately, with Kubernetes DNS, this is simply changing the gateway parameter like this faas-cli invoke nodeinfo -g http://gateway.othernamespace:8080

Authentication

If you want to use a faas-cli command that requires authentication, you can mount your basic authentication secret and pass it to faas-cli login.

You could then update the CronJob to login, like this:

# nodeauth-cron.yaml
apiVersion: batch/v1beta1
kind: CronJob
metadata:
  name: nodeinfo-auth
  namespace: openfaas
spec:
  schedule: "*/1 * * * *"
  concurrencyPolicy: Forbid
  successfulJobsHistoryLimit: 1
  failedJobsHistoryLimit: 3
  jobTemplate:
    spec:
      template:
        spec:
          containers:
          - name: openfaas-cli
            image: ghcr.io/openfaas/faas-cli:latest
            env:
              - name: USERNAME
                valueFrom:
                  secretKeyRef:
                    name: basic-auth
                    key: basic-auth-user
              - name: PASSWORD
                valueFrom:
                  secretKeyRef:
                    name: basic-auth
                    key: basic-auth-password
            command:
            - /bin/sh
            args:
            - -c
            - echo -n $PASSWORD | faas-cli login -g http://gateway.openfaas:8080 -u $USERNAME --password-stdin
            - echo "verbose" | faas-cli invoke nodeinfo -g http://gateway.openfaas:8080
          restartPolicy: OnFailure