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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 this to send out a report email on a daily basis, to update some cached data every 10 minutes, or to update some summary information once an hour.
A cron job will invoke a URL at a given time of day. A URL invoked by cron is subject to the same limits and quotas as a normal HTTP request, including the request time limit.
An application can have up to 20 scheduled tasks.
A cron.yaml
file in the root directory of your application (alongside app.yaml
) configures scheduled tasks for your Python application. The following is an example cron.yaml
file:
cron: - description: daily summary job url: /tasks/summary schedule: every 24 hours - description: monday morning mailout url: /mail/weekly schedule: every monday of month 09:00 timezone: Australia/NSW
The syntax of cron.yaml
is the YAML format. For more information about this syntax, see the YAML website for more information.
A cron.yaml
file consists of a number of job definitions. A job definition must have a url
and a schedule
. You can also optionally specify a description
and a timezone
. The description will be visible in the Admin Console and the development server's admin interface.
The url
field specifies a URL in your application that will be invoked by the Cron Service. See Securing URLs for Cron for more. The format of the schedule field is covered in The Schedule Format.
The timezone should be the name of a standard zoneinfo time zone name. If you don't specify a timezone, the schedule will be in UTC (also known as GMT).
Cron schedules are specified using a simple English-like format.
The following are examples of schedules:
every 5 minutes every 12 hours 2nd,third mon,wed,thu of march 17:00 every monday of month 09:00 1st monday of sep,oct,nov 17:00
If you don't need to run a recurring job at a specific time, but instead only need to run it at regular intervals, use the form: every N (hours|mins|minutes)
, where N is a number and hours or minutes specifies the unit of time. The shortest time between runs of a task that can be specified is 1 minute.
If you want more specific timing, you can specify the schedule as:
("every"|ordinal) (days) "of" (monthspec) (time)
The brackets are for illustration only, and quotes indicate a literal.
Where:
A cron handler is just a normal handler defined in app.yaml
. 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 restrict a URL by adding login: admin
to the handler configuration in app.yaml
.
An example might look like this in app.yaml
:
application: hello-cron version: 1 runtime: python api_version: 1 handlers: - url: /report/weekly script: reports.py login: admin
For more information see Python Application Configuration: Requiring Login or Administrator Status.
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: true
If you wish to ensure that only cron requests can trigger your handler, you should check for that header.
You can use appcfg.py
to upload cron jobs and view information about the defined cron jobs. When you upload your application to App Engine using appcfg.py update
, the Cron Service is updated with the contents of cron.yaml
. You can update just the cron configuration without uploading the rest of the application using appcfg.py update_cron
.
To delete all cron jobs, change the cron.yaml
file to just contain:
cron:
You can display the parsed version of your cron jobs, including the times the jobs will run, using the appcfg.py cron_info
command.
If you want appcfg.py cron_info
to correctly handle timezones you have specified, install the pytz package.
The Admin Console allows you to view the state of your cron jobs. Select the "Cron Jobs" link from the side menu to view the state of the jobs, including the last time the job was run and the result of the job.
You can also see when cron jobs are added or removed by selecting the "Admin Logs" page from the Admin Console menu.
When using the Python SDK, the dev_appserver has an admin interface that allows you to view cron jobs at /_ah/admin/cron
.
The development server doesn't automatically run your cron jobs. You can use your local desktop's cron or scheduled tasks interface to trigger the URLs of your jobs with curl or a similar tool.