I mean, running multiple node runtimes (aka multiprocessing) actually sounds like a reasonable compromise for parallelism. That's the standard solution for dynamic languages without great multithreading support. If you needed great multithreading support then Node probably wasn't the right choice for you in the first place, but for most applications, it's probably fine.

However, running multiple containers for parallelism sounds a little bit crazy. In the worst case, each container may be running on its own server, but even assuming multiple containers per host, I'm guessing they were running an insignificant number of instances, which is probably why they were able to save $300k in server costs.