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AWS Community Builders profile image Rey Abolofia
Rey Abolofia for AWS Community Builders

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Serverless wsgi zipped packages

I just spent the longest time trying to debug why my Flask app run on AWS Lambda wasn't working correctly. Consistently, I was seeing the error,

No module named 'wsgi_handler'
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I was able to track this down to how I am packaging my function. I create a zip file containing my function code and its requirements. Using Serverless Framework, this looks like,

package: artifact: .package/package.zip
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I was then using the plugin serverless-wsgi to serve my Flask app.

The problem was that the serverless-wsgi plugin was unable to include its required wsgi_handler code file. This is because my code was already zipped before running serverless deploy.

The solution was to remove the serverless-wsgi plugin and wrap the handler manually.

  1. Install serverless-wsgi as a python dependency 
 $ pip install serverless-wsgi $ pip freeze > requirements.txt
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  1. Create the lambda handler 
 # file handlers/ui_handler/__init__.py  import serverless_wsgi from handlers.ui_handler.app import app def handle(event, context): return serverless_wsgi.handle_request(app, event, context)
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  1. Using Serverless Framework, set the handler to this function 
 functions: ui: handler: handlers/ui_handler.handle url: true
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