Subscribing to cron events

Determine your cron interval

The cron event producer generates events at regular intervals. This interval can be scheduled by minute, hour, day, or month or a combination of several different time intervals.

Cron uses a standard crontab to specify interval details, in the format * * * * *, which stands for minute, hour, day of month, month, and day of week. For example, to schedule an event for midnight, specify 0 0 * * *. To schedule an event for every Friday at midnight, specify 0 0 * * FRI.

For more information about crontab, see CRONTAB.

You can set your cron interval by using the --schedule option with the subscription cron command, as shown in Step 3. If you do not specify the --schedule option, then by default, the cron event is sent every minute of every day.

Create your app (or job)

While events can be used to trigger apps or jobs, this tutorial uses an app.

Create your application called cron-app with the ibmcloud ce app create command. This app pulls an image that is called icr.io/codeengine/cron. This app logs each event as it arrives, showing the full set of HTTP Headers and HTTP Body payload. For more information about the code that is used for this example, see cron.

ibmcloud ce app create --name cron-app --image icr.io/codeengine/cron 

Run ibmcloud ce application get --name cron-app to verify that your app is in a Ready state.

You can find more information about this app at cron readme file.

Create a subscription

After your app is ready, create a subscription to the cron event producer and connect it to your app with the ibmcloud ce sub cron create command.

The following example creates a cron subscription that is called cron-sub and specifies the cron-app application as its destination. The subscription uses the --data option to include a JSON string in the cron event. It also specifies the cron schedule by using the --schedule option with a value of * * * * * to send an event every minute of every day to the cron-app application.

ibmcloud ce sub cron create --name cron-sub --destination cron-app --data '{"mydata":"hello world"}' --schedule '* * * * *'

Run ibmcloud ce sub cron get -n cron-sub to find information about your subscription.

Example output

In this output, you can see that the subscription name, destination, schedule, and data are correct.

Getting cron event subscription 'cron-sub'...
OK

Name:          cron-sub  
ID:            abcdefgh-abcd-abcd-abcd-1a2b3c4d5e6f 
Project Name:  myproject  
Project ID:    01234567-abcd-abcd-abcd-abcdabcd1111  
Age:           2m18s  
Created:       2021-03-14T13:21:13-05:00   

Destination Type:  app  
Destination:       cron-app  
Schedule:          * * * * *  
Time Zone:         UTC  
Data:              {"mydata":"hello world"}  
Ready:             true  

Events:    
    Type     Reason                 Age                Source                 Messages   
    Normal   FinalizerUpdate        65s                pingsource-controller  Updated "cron-sub" finalizers 

Testing your subscription

After you successfully subscribed your app to your cron event, look at the logs to see whether it works.

Get the logs for the app with the ibmcloud ce app logs command.

ibmcloud ce app logs --name cron-app

Example output

In the following output, you can see that the date and time that the event was received as well as the HTTP Headers and the HTTP Body JSON that was passed in when the subscription was created.

2021-01-21 20:15:00 - Received:  
Header: Accept-Encoding=[gzip]  
Header: Ce-Id=[7de01e8e-84dc-4409-ad56-90d6e391397c]  
Header: Ce-Source=[/apis/v1/namespaces/50d38123af5/pingsources/cron-sub]  
Header: Ce-Specversion=[1.0]  
Header: Ce-Time=[2021-01-21T20:15:00.392503458Z]  
Header: Ce-Type=[dev.knative.sources.ping]  
Header: Content-Length=[24]  
Header: Content-Type=[application/json]  
Header: Forwarded=[for=172.30.118.174;proto=http, for=172.30.95.204]  
Header: K-Proxy-Request=[activator]  
Header: Traceparent=[00-1bf4b6b1d67f278a4b827e4e00f0cf7c-cbce9df0faedd812-00]  
Header: User-Agent=[Go-http-client/1.1]  
Header: X-B3-Sampled=[0]  
Header: X-B3-Spanid=[fb208eaa6af15ede]  
Header: X-B3-Traceid=[6db074fdaf6a6411fb208eaa6af15ede]  
Header: X-Envoy-Attempt-Count=[1]  
Header: X-Envoy-Decorator-Operation=[cron-app-snva7-1.50d38123af5.svc.cluster.local:80/*]  
Header: X-Envoy-Internal=[true]  
Header: X-Envoy-Peer-Metadata=[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]  
Header: X-Envoy-Peer-Metadata-Id=[router~172.30.95.204~istio-ingressgateway-d76569c9-l9pvh.istio-system~istio-system.svc.cluster.local]  
Header: X-Forwarded-For=[172.30.118.174, 172.30.95.204, 172.30.163.42]  
Header: X-Forwarded-Proto=[http]  
Header: X-Request-Id=[ce502e5e-dd89-401e-a4cd-b72a6822f689]  

Body: {"mydata":"hello world"}  

For more information about headers and body, see HTTP headers and body information for cron events.

For more information about viewing logs with the CLI, see Viewing logs with the CLI.

Note that subscriptions can affect how an application scales. For more information, see Configuring application scaling.

Update your subscription

Now that you know that your cron subscription is successful, you can update the cron event to run on a different schedule with the ibmcloud ce sub cron update command. For example, update the subscription to run every day at midnight.

ibmcloud ce sub cron update -n cron-sub -d cron-app --data '{"mydata":"hello world again"}' -s '0 0 * * *'

Run the ibmcloud ce sub cron get -n cron-sub command to find information about your subscription.

Example output

In this output, you can see that the schedule and data are updated.

Getting cron event subscription 'cron-sub'...
OK

Name:          cron-sub  
ID:            abcdefgh-abcd-abcd-abcd-1a2b3c4d5e6f
Project Name:  myproject  
Project ID:    01234567-abcd-abcd-abcd-abcdabcd1111 
Age:           5m7s  
Created:       2021-03-14T13:21:13-05:00   

Destination:  App:cron-app  
Schedule:     0 0 * * *  
Data:         {"mydata":"hello world again"}  
Ready:        true

Events:    
    Type     Reason                 Age                Source                 Messages   
    Normal   FinalizerUpdate        65s                pingsource-controller  Updated "cron-sub" finalizers 

Clean up for cron subscription tutorial

Ready to delete your cron subscription and your app? You can use the ibmcloud ce app delete and the ibmcloud ce sub cron delete commands.

To remove your subscription,

ibmcloud ce sub cron delete --name cron-sub

To remove your application,

ibmcloud ce app delete --name cron-app

Looking for more code examples? Check out the Samples for IBM Cloud Code Engine GitHub repo.