VCR.py is a python version of the Ruby VCR library. When testing code that makes HTTP requests, VCR.py can make your tests faster, more reliable and more secure, and in general just make your life a lot easier.

VCR works by recording HTTP requests and responses generated while running tests, and serializing them into a cassette file. Future HTTP requests are intercepted and the recorded reponse is returned withouth ever connecting to the original HTTP host. This means that once the cassette is recorded, the tests can still be executed even if there is no internet connection, or the host is unavailable for some reason.

Another useful feature of VCR is that it can obscure sensitive API tokens and passwords in the cassette, and a real token or password is no longer needed once the cassette has been recorded. This means that developers can run the tests without even having access to a valid token or password!

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Prerender is an open source tool for making single page applications available for search engine indexing. It runs as a Node.js server that can easily be deployed to Heroku, which is how we were using it for PartCycle.com before moving to AWS. There is also the option of subscribing to the Prerender.io service and skipping hosting altogether.

Self-hosting with Heroku would probably be more than adequate for most people using prerender. However, for large e-commerce applications where there might be hundreds of thousands or even millions of items available (and thus unique content URLs), handling the volume of Google bot requests can become quite expensive.

Thankfully Amazon Web Services comes to the rescue with their cheap but powerful EC2 instances. Using OpsWorks, it is fairly straightforward and painless to configure a small, scalable prerender cluster that can can handle rendering hundreds of pages per minute at a fraction of the cost of an equivalent Heroku configuration.

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