The App Engine Cron Service allows you to configure regularly scheduled tasks that operate at defined times or regular intervals. These tasks are commonly known as cron jobs. These cron jobs are automatically triggered by the App Engine Cron Service. For instance, you might use a cron job to send out an email report on a daily basis, or to update some cached data every 10 minutes, or refresh summary information once an hour.
A cron job makes an HTTP
GET request to a URL as scheduled. The handler for
that URL executes the logic when it is called.
A cron job request is subject to the same limits as those for
push task queues.
Creating a cron job
- Create the
cron.xmlfile in the
WEB-INF/directory of your application (alongside
Add one or more
<cron>entries to your file and define the necessary elements for your job, including the required
The following example creates a basic cron job that runs daily:
<?xml version="1.0" encoding="UTF-8"?> <cronentries> <cron> <url>/tasks/summary</url> <target>beta</target> <description>daily summary job</description> <schedule>every 24 hours</schedule> </cron> </cronentries>
The target specification is optional and is the name of a service/version. If present, the target is prepended to your app's hostname, causing the job to be routed to that service/version. If no target is specified, the job will run in the versions of the
defaultservice that are configured for traffic.
Create a handler for the cron job's URL. The handler should execute any tasks that you want scheduled. The handler should respond with an HTTP status code between 200 and 299 (inclusive) to indicate success. Other status codes can be returned and can be used to trigger.
The handler can be as simple as a Servlet in the app. The Servlet's URL mapping in the web.xml file should be the same as the cron job's URL.
retrying the job.
For more information about the syntax and parameters of the cron.xml, see the cron.xml reference.
Testing cron jobs in the development server
The local development server (dev_appserver) doesn't automatically run your cron jobs. You can make requests directly to your cron job's URL to test your functionality. You can use your local cron or scheduled tasks interface to trigger the URLs of your jobs with curl or a similar tool.
Uploading cron jobs
You can use the
tool to upload your cron jobs to App Engine.
- Option 1: Upload your whole application
To upload your whole application, which also updates the Cron Service with the entries from your
cron.xmlfile, run the following command:
./appengine-java-sdk/bin/appcfg.sh -A your-app-id -V app-version update [YOUR_APP_DIR]
- Option 2: Upload only your cron updates
To update just the cron configuration without uploading the rest of the application, run the following command:
./appengine-java-sdk/bin/appcfg.sh -A your-app-id -V app-version update_cron [YOUR_APP_DIR]
Deleting all cron jobs
To delete all cron jobs:
Edit the contents of the
<?xml version="1.0" encoding="UTF-8"?> <cronentries/>
Retrying cron jobs that fail
If a cron job's request handler returns a status code that is not in the range 200–299 (inclusive) App Engine considers the job to have failed. By default, failed jobs are not retried.
To set failed jobs to be retried:
- Include a
retry-parametersblock in your
Choose and set the retry parameters in the
For example, this sample
cron.xmlfile contains a single cron job that is configured to retry up to five times (the default) with a starting backoff of 2.5 seconds that doubles each time.
<cronentries> <cron> <url>/retry</url> <description>Retry on jsdk</description> <schedule>every 10 minutes</schedule> <retry-parameters> <min-backoff-seconds>2.5</min-backoff-seconds> <max-doublings>5</max-doublings> </retry-parameters> </cron> </cronentries>
Securing URLs for cron
You can prevent users from accessing URLs used by scheduled tasks by restricting
access to administrator accounts. Scheduled tasks can access admin-only URLs.
You can read about restricting URLs at Security and
An example you would use in
web.xml to restrict everything starting with
/cron/ to admin-only is:
<security-constraint> <web-resource-collection> <web-resource-name>cron</web-resource-name> <url-pattern>/cron/*</url-pattern> </web-resource-collection> <auth-constraint> <role-name>admin</role-name> </auth-constraint> </security-constraint>
For more on the format of
web.xml, see the documentation on the deployment
To test a cron job, sign in as an administrator and visit the URL of the handler in your browser.
Requests from the Cron Service will also contain a HTTP header:
X-Appengine-Cron header is set internally by Google App Engine. If your
request handler finds this header it can trust that the request is a cron
request. If the header is present in an external user request to your app, it
is stripped, except for requests from logged in administrators of the
application, who are allowed to set the header for testing purposes.
Google App Engine issues Cron requests from the IP address
Calling Google Cloud Endpoints
You cannot specify a Google Cloud Endpoint in
url field of a cron job.
If you want your cron job to call a Google Cloud Endpoint,
issue a request to a target that is served by a handler in
your app, and call the endpoint class and method from the handler code.
Viewing cron jobs in the GCP Console
The GCP Console Task queues page has a tab that shows the tasks that are running cron jobs.
You can also visit the Logs page see when cron jobs were added or removed.