Using a pid-file that's implied by the ingestion directory.
We do this in `get_pc_registry`, i.e. on the first request. This means failure is
in the first request on the 2nd process.
Why not on startup? Because we don't have a configtest or generic on-startup location
(yet). Making _that_ could be another source of fragility, and getting e.g. the nr
of processes might be non-trivial / config-dependent.
Why?
> One is that WhiteNoise is designed to work in situations where Apache, nginx
> and the like aren’t easily available. But more importantly, it’s easy to
> underestimate what’s involved in serving static files correctly
We deal with both these situations:
* for local development, we recommend running with DEBUG=False and still want to
sever staticfiles
* for deploying using nginx/whatever, I'd like to keep my instructions as simple
as possible, and doing this right once (in whitenoise) saves us from having to
come up with the right instructions for a bunch of webservers.
Klaas van Schelven