1) All features/algorithms were ported, and we only added new functionality that never existed in the old Python code base. A few of the features that got added include: dispatching builds, getting live logs, re-encrypt keys, deploy encrypted artifacts, fix many bugs, support running multiple agents on a single computer, etc. I should also mention that we previously had two separate downloads: a CLI used for uploading releases, and the agent used for dispatching deployments. The functionality of both of these code bases where merged into our new Lua based "client" so customers only have to install a single binary that is less than 10MB (the binary size depends on your platform).

2) Deployments with the new agent were noticeably faster, (like 1 second deployments that used to take 20+ seconds). However, this speed up was largely due to the Python codes design which had a "continuation" loop which was polling based, but the Lua code used coroutines and simply continued the threads when the steps were complete.

Overall, I think the choice to use Lua (or more specifically luvi) was a great decision. Note that it did take a few iterations in order to come up with the optimal way of using Lua + libuv. Originally I was taking the Node.JS approach of using callbacks, but that approach has two problems:

[a] It is difficult to properly implement "back pressure" so that all queues between producer and consumer are bounded.

[b] It is difficult to handle errors properly.

Lua coroutines allowed me to write a simple "green thread" library that encapsulated these challenges.