Setting up cron job in google app engine python

Question

I'm just getting started with Google App Engine so I'm still learning how to configure everything. I wrote a script called parsexml.py that I want to run every 10 minutes or so. This file is in my main directory, alongside main.py, app.yaml, etc. As I understand it, I need to create a new file, cron.yaml which looks like this:

cron:
- description: scrape xml
  url: /
  schedule: every 10 minutes

I'm not sure what I need to put in the url field. I'm also not sure if anything else is needed. Do I need to change my app.yaml file at all? Where do I specify the name of my parsexml.py file?

Answer 1

Brian,

You'll need to update both your app.yaml and cron.yaml files. In each of these, you'll need to specify the path where the script will run.

app.yaml:

handlers:
- url: /path/to/cron
  script: parsexml.py

or if you have a catch all handler you won't need to change it. For example:

handlers:
- url: /.*
  script: parsexml.py

cron.yaml:

cron:
- description: scrape xml
  url: /path/to/cron
  schedule: every 10 minutes

As in the documentation, in parsexml.py you'll need to specify a handler for /path/to/cron and register it with a WSGI handler (or you could use CGI):

from google.appengine.ext import webapp
from google.appengine.ext.webapp.util import run_wsgi_app

class ParseXMLHandler(webapp.RequestHandler):
    def get(self):
        # do something

application = webapp.WSGIApplication([('/path/to/cron', ParseXMLHandler)],
                                     debug=True)
if __name__ == '__main__':
    run_wsgi_app(application)

Note: If you are using the Python 2.7 runtime, you will want to specify script: parsexml.application where application is a global WSGI variable for handling requests.

Answer 2

In GAE, all actions are done via URLs. You can't just run an arbitrary script as a cron: you need to make that script a handler and give it a URL, like any other view in your project.

So, map a URL to your script in app.yaml, edit the script to make it a handler, and use that URL in cron.yaml.

Answer 3

The url is used to run the py script for your cron job

basically in your app.yaml

you have

app.yaml
handlers:
- url: /helloworld.py
  script: helloworld.py

in cron.yaml

cron.yaml
- description: scrape xml
  url: /helloworld.py
  schedule: every 10 minutes

if you want the cron to run hello world you have to set the url as url: /helloworld.py