There is a Cosmic Background level of DERP Unreachability,
with individual nodes or regions becoming unreachable briefly
and returning a short time later. This is due to hosting provider
outages or just the Internet sloshing about.
Returning a 500 error pages a human. Being awoken at 3am for
a transient error is annoying.
For relatively small levels of badness don't page a human,
just post to Slack. If the outage impacts a significant fraction
of the DERP fleet, then page a human.
Signed-off-by: Denton Gentry <dgentry@tailscale.com>
