There is already an (unofficial Google) image proxy written in Go that is quite fast, does caching (local or backed by S3/GCS), and does other nice things like smart cropping: https://github.com/willnorris/imageproxy
Seemed like a lot of unnecessary work for them to reimplement a service from scratch without gaining any major perf benefits over their existing one and without leaning on an existing well-known and well-built foundation.
Author of the blog post here - it looks like what you linked does its image resizing in pure Go. In our testing we found these libraries are significantly slower than the C++ resize libraries. I would guess we would need at least 10x as many instances if we used that resizer, though probably a lot more
The one thing these don't support though is smarter cropping that takes into account image contents, which takes enough cpu power to require preprocessing
Seemed like a lot of unnecessary work for them to reimplement a service from scratch without gaining any major perf benefits over their existing one and without leaning on an existing well-known and well-built foundation.