CODEWITHSUNDEEP
pythongoogle-app-enginecron
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Reputation: 265

How can I run a script constantly in background of App Engine website?

I'm trying to use Google App Engine (Python) to make a simple web app. I want to maintain one number x in the datastore that models a random walk. I need a script running 24 hours a day that, every second, randomly chooses to either increment or decrement x (saving the change to the datastore). Users should be able to go to a url to see the current value of x.

I've thought of two ways to accomplish the constant script issue:

1) I can have an admin-access page that runs a continuous loop in javascript which, each second, makes an AJAX request to the server to update x. If I leave this page open on my computer 24 hours a day, this should work. The problem with this approach is that if my computer crashes then the script dies with it.

2) I can use a CRON job. But the interval between jobs cannot be smaller than 1 minute, so this doesn't really work.

It seems like there should be a simple way to just run a script constantly (that exists only server side) with Google App Engine.

I appreciate any advice. Thanks for your time!

Upvotes: 1

Views: 1013

Answers (1)

Andrei Volgin
Andrei Volgin

Reputation: 41099

Start a backend instance using Modules (either programmatically or by hitting a special URL accessible to admins only). Run the script for as long as the instance lives.

Note that an instance can die, just like your computer can crash. For this reason, you are probably better off with a Google Compute Engine instance (choose the smallest) than with an App Engine instance. Note that the Compute Engine instance will be many times cheaper.

Compute Engine instances can also fail, though it is much less likely. There are ways to create a fail-over implementation (when one instance is creating your random numbers while the other instance - which can run on some other platform - waits for the first one to fail), but this will obviously cost more.

Upvotes: 3

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