Configuring Warmup Requests to Improve Performance

This guide describes how to configure your app to handle warmup requests. With warmup requests enabled, the App Engine infrastructure issues GET requests to /_ah/warmup. You can implement handlers for this request to perform application-specific tasks, such as pre-caching application data.

Enabling warmup requests

Warmup requests work only if the minimum number of idle instances has been manually set in the app.yaml file. If a scaling mode has not been specified in the app.yaml file, the default value is Auto for the min_idle_instances element and warmup requests will not be sent.

In Python, warmup requests are disabled by default. To enable them, add -warmup to the inbound_services directive in app.yaml:

inbound_services:
- warmup

Registering your handler

To register your handler, define the script to handle your warmup requests in your app.yaml file. For example:

application: your_project_id
# ...
inbound_services:
- warmup

handlers:
- url: /_ah/warmup
  script: main.py
  login: admin

This example registers a handler to listen to warmup requests to the /_ah/warmup request path with the `main.py` file.

Creating your handler

Build any logic that you need to run into a handler that you map to respond to the /_ah/warmup request path. The following example builds on the previous example:

import webapp2

class MyWarmUpCode(webapp2.RequestHandler):
  """
  This class handles the warmup request. You should add any code that you
  need to execute in the `get` method, such as populating caches, and ensure
  that you return a successfull HTTP response.
  """

  def get(self):

      # Your warmup logic goes here.

      # Return a successful response to indicate the logic completed.
      self.response.headers['Content-Type'] = 'text/plain'
      self.response.write('Warmup successful')

  # ...

application = webapp2.WSGIApplication(
    [
        ('/_ah/warmup', MyWarmUpCode),
        # Other handlers
        # ...
    ]
)

What's next

The examples above provide a framework to work within. Next, you'll want to decide what logic belongs in your warmup request handlers. You might want to add values into memcache that your application will need. For example, if you build and store a list of the current trending articles for your site, building that list in the warmup and then storing the necessary data in memcache means that when a user request comes in, the application has everything ready to serve and no queries are performed on the user's request for that data, which results in a faster response.

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