This repo contains Casper, a caching proxy internal to Yelp. It is built with Nginx and Openresty at its core and contains some logic in Lua to fit in our ecosystem.

Important note about naming: Casper was initially baptized "Spectre" internally. It's only after the Spectre/Meltdown vulnerabilities were published that we decided to change the name to "Casper", a more friendly and less confusing name for the outside world. If you see remnants of "Spectre" in the code, that's why!

• docker: make sure it's installed on your system by following the instruction for your platform here.
• make: ensure you can run make targets with your OS (on Windows, use nmake.)
• lua 5.1
• luarocks
• openresty: follow the instructions at https://openresty.org/en/installation.html

On macos you can install most of those packages easily via homebrew (https://brew.sh/). Just run brew install lua@5.1 openresty/brew/openresty luarocks make.

To start Casper, run

$ make dev

To make sure it's up (change the port accordingly if you change the default):

$ curl -v localhost:8888/status

For basic debugging (is it missing/hitting the cache? Am I being correctly proxied? etc), curl, and pay attention to the "Spectre-Cache-Status" header:

$ curl -o /dev/null -iv -H 'X-Source-Id: test' -H 'X-Smartstack-Destination: yelp-main.internalapi' -H 'X-Smartstack-Source: spectre.main' -H 'Host: internalapi' 'localhost:32927/category_yelp/?locale=en_US' 2>&1 | grep 'Spectre-Cache-Status'
< Spectre-Cache-Status: hit

It can help, to get as much information as possible, to set nginx logging to debug granularity. In nginx.conf, replace the error_log directive by:

error_log /var/log/nginx.debug.log debug;

To run unit tests:

$ make test

To run integration tests:

$ make itest

Casper was built and developed internally for about a year before being opensourced. In addition to the contributors listed on Github, here is a list of people who contributed to Casper before its public life:

• Angelo Licastro (@angelolicastro)
• Anthony Tan (@DevelopingCoder)
• Arnaud Brousseau (@arnaudbrousseau)
• Avadhut Phatarpekar (@avadhutp)
• Bai Li (@luckytoilet)
• Ben Plotnick (@bplotnick)
• Chris Kuehl (@chriskuehl)
• Daniele Rolando (@drolando)
• Ishan Vashishtha (@ishanvas)
• Mayank Sindwani (@msindwan)
• Michael Bryant (@mjbryant)

We welcome contributions to Casper, but keep in mind that this is a production system run inside of Yelp's infrastructure. Please get in touch with us to discuss your feature request, bug fix or enhancement by opening a Github issue.