this works by having every request from the functions server kick back a
FXLB-WAIT header on every request with the wait time for that function to
start. the lb then keeps track on a per node+function basis an ewma of the
last 10 request's wait times (to reduce jitter). now that we don't have max
concurrency it's actually pretty challenging to get the wait time stuff to
tick. i expect in the near future we will be throttling functions on a given
node in order to induce this, but that is for another day as that code needs a
lot of reworking. i tested this by introducing some arbitrary throttling (not
checked in) and load spreads over nodes correctly (see images). we will also
need to play with the intervals we want to use, as if you have a func with
50ms run time then basically 10 of those will rev up another node (this was
before removing max_c, with max_c=1) but in any event this wires in the basic
plumbing.
* make docs great again. renamed lb dir to fnlb
* added wait time to dashboard
* wires in a ready channel to await the first pull for hot images to count in
the wait time (should be otherwise useful)
future:
TODO rework lb code api to be pluggable + wire in data store
TODO toss out first data point containing pull to not jump onto another node
immediately (maybe this is actually a good thing?)
