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?)
this patch gets rid of max concurrency for functions altogether, as discussed,
since it will be challenging to support across functions nodes. as a result of
doing so, the previous version of functions would fall over when offered 1000
functions, so there was some work needed in order to push this through.
further work is necessary as docker basically falls over when trying to start
enough containers at the same time, and with this patch essentially every
function can scale infinitely. it seems like we could add some kind of
adaptive restrictions based on task run length and configured wait time so
that fast running functions will line up to run in a hot container instead of
them all creating new hot containers.
this patch takes a first cut at whacking out some of the insanity that was the
previous concurrency model, which was problematic in that it limited
concurrency significantly across all functions since every task went through
the same unbuffered channel, which could create blocking issues for all
functions if the channel is not picked off fast enough (it's not apparent that
this was impossible in the previous implementation). in any event, each
request has a goroutine already, there's no reason not to use it. not too hard
to wrap a map in a lock, not sure what the benefits were (added insanity?) in effect
this is marginally easier to understand and less insane (marginally). after
getting rid of max c this adds a blocking mechanism for the first invocation
of any function so that all other hot functions will wait on the first one to
finish to avoid a herd issue (was making docker die...) -- this could be
slightly improved, but works in a pinch. reduced some memory usage by having
redundant maps of htfnsvr's and task.Requests (by a factor of 2!). cleaned up
some of the protocol stuff, need to clean this up further. anyway, it's a
first cut. have another patch that rewrites all of it but was getting into
rabbit hole territory, would be happy to oblige if anybody else has problems
understanding this rat's nest of channels. there is a good bit of work left to
make this prod ready (regardless of removing max c).
a warning that this will break the db schemas, didn't put the effort in to add
migration stuff since this isn't deployed anywhere in prod...
TODO need to clean out the htfnmgr bucket with LRU
TODO need to clean up runner interface
TODO need to unify the task running paths across protocols
TODO need to move the ram checking stuff into worker for noted reasons
TODO need better elasticity of hot f(x) containers
