The future of compute is fine-grained. Cloudflare Workers is all about fine-grained compute, that is, splitting compute into small chunks -- a single HTTP request, rather than a single server instance. This is what allows us to run every customer's code (no matter how little traffic they get) in hundreds of locations around the world, at a price accessible to everyone.

The finer-grained your compute gets, the higher the overhead of strict process isolation gets. At the point Cloudflare is operating at, we've measured that imposing strict process isolation would mean an order of magnitude more overhead, in terms of CPU and memory usage. It depends a bit on the workload of course, but it's big. Yes, this is with all the tricks, zygote processes, etc.

We have plenty of defense-in-depth that we can do instead of process isolation, that doesn't have such enormous cost. [0] [1]

IMO, the platforms that stubbornly insist that process isolation is the only answer are the ones that are going to lose out eventually, just as bare metal has been supplanted by VMs, which are in turn being replaced by containers, etc. Over time we move to finer-grained primitives because doing so unlocks more power.

[0] https://blog.cloudflare.com/mitigating-spectre-and-other-sec...

[1] https://blog.cloudflare.com/spectre-research-with-tu-graz/