this structure should allow us to keep the consistent hash code and just use
consistent hashing on a subset of nodes, then in order to satisfy the oracle
service stuff in functions-service we can just implement a different "Grouper"
that does vm allocation and whatever other magic we need to manage nodes and
poop out sets of nodes based on tenant id / func.
for the suga... see main.go and proxy.go, the rest is basically renaming /
moving stuff (not easy to follow changes, nature of the beast).
the only 'issues' i can think of is that down in the ch stuff (or Router) we
will need a back channel to tell the 'Grouper' to add a node (i.e. all nodes for
that shard are currently loaded) which isn't great and also the grouper has no
way of knowing that a node in the given set may not be being used anymore.
still thinking about how to couple those two. basically don't want to have to
just copy that consistent hash code but after munging with stuff i'm almost at
'fuck it' level and maybe it's worth it to just copy and hack it up in
functions-service for what we need. we'll also need to have different key
funcs for groupers and routers eventually (grouper wants tenant id, router
needs tenant id + router). anyway, open to any ideas, i haven't come up with
anything great. feedback on interface would be great
after this can plumb the datastore stuff into the allGrouper pretty easily
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?)
