Monday, July 20, 2015

Bluemix: Simple cron-like service for my Python code

Schedule background tasks in Bluemix
This morning I had some time to fiddle around with Bluemix and Python. I wanted to test out creating a cron-like service, i.e., something that runs in the background and kicks off tasks with given intervals or at a given time. For Python there exists a package "schedule" that is easy to set up and use. So how do you create a background service in Bluemix?

The trick is in the file manifest.yml and the Cloudfoundry documentation has all the needed details (Bluemix is built on this open standard). The attribute "no-route" is set to true, indicating that this is not a Web application and we don't need a subdomain name. In addition the attribute "command" is set to invoke the Python interpreter with my script as parameter. Basically, this starts my background task:

 applications:  
 - name: hltimer  
  memory: 256M  
  instances: 1  
  no-route: true  
  command: python mytimer.py  
  path: .  


The cron-like service script is pretty simple. It uses the "schedule" package to set up recurring jobs. I tested it with the Twilio API to send me SMS at given timestamps. You can also use it to scrape webpages in given intervals, kick off feed aggregators, read out sensors and update databases like Cloudant or DB2, and more. See this Github repository for the full source.

 import schedule  
 import time 

 def job():  
 #put the task to execute here  

 def anotherJob():  
 #another task can be defined here  

 schedule.every(10).minutes.do(job)  
 schedule.every().day.at("10:30").do(anotherJob)  

while True:  
   schedule.run_pending()  
   time.sleep(1)  

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