AWS ElasticBeanstalk custom environment variables

As a holiday project I’ve been looking into using Jenkins to deploy code updates from GitHub into an Amazon AWS ElasticBeanstalk instance[1] as an early attempt at some sort of continuous delivery.

One of the features of the Flask application is that it tries to get the SECRET_KEY from an environment variable (although the code for a failsafe value doesn’t work: FIXME). The intention is that the web server environment provides the key at runtime so that different values can be used in each environment.

Now, this AWS page describes the format of the options to apply custom environment settings to an application (the name of the actual file doesn’t matter so long as it is called .config and is found in the .ebextensions directory in the uploaded code):

option_settings:
  aws:elasticbeanstalk:application:environment:
    SECRET_KEY: ChangeMe
  aws:elasticbeanstalk:container:python:
    WSGIPath: crossword_hints.py

Setting the WSGIPath variable means that I can continue to use the original application source file rather than change to the default application.py.

This file can safely be kept in the GitHub repo and setup as a simple shell build step in Jenkins prior to the code upload, thus:

SECRET_KEY=`openssl rand -base64 12`; sed -ie "s/ChangeMe/${SECRET_KEY}/" .ebextensions/options.config

Jenkins has a great AWS EB deploy plugin that uses stored credentials to mange the source bundling, upload and deployment of the application; it’s kinda strange seeing the AWS console page spring into life in response to the Jenkins job running. To save having to include the build shell step, I’m thinking of creating my own version of the plugin that allows the inclusion of custom variables.

[1] – As a development instance the application will be mostly terminated (and offline) because AWS is a very expensive way of running a bit of demo code.

References

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