A fairly simple reverse-proxy and cache server writting in GoLang, primarily inspired by Varnish

Goals

• Request coalescing
• Vary support
• Respect cache control header
  • private, public, no-cache, no-store, max-age, s-maxage
  • no-cache (properly this time), stale-if-error, stale-while-revalidate
• Query string sorting
• Latency-based origin loadbalancing
• Cache tag/purge by tag support
• Memory mapped cache(?)

Notes

• How do you properly do request coalescing for requests that can vary? e.g. if a bunch of requests come in for an image, they get coalesced into a single origin request, but that origin request may contain an Accept header that allows for a mime-type that not all requests that were coalesced together accept.
  • You can maybe do this somewhat intelligently by only coalescing requests together if they share accept and accept-encoding values?
• Implementing stale-if-error and stale-while-revalidate seem like they'll be a pain. You'd need to intelligently keep things in cache after they've expired

Performance

Results of some benchmarks from requesting the same asset repeatedly (all cache hits)

Request rate	Total requests made	Avg response time	Median response time	Min response time	Max response time	Response time Std. Dev.
~39k RPM	11167	86.1µs	69µs	17µs	4.7ms	144.6µs
~97k RPM	40899	63.1µs	37.8µs	15.8µs	9.5ms	134µs

Features

Request Coalescing

If multiple requests for the same cache entry are received at the same time, only

Full support for Vary header

Varies the cache based on values of headers listed in the Vary response header. There are currently no disallowed headers, even things like User-Agent