ExRated, the Elixir OTP GenServer with the naughty name that allows you to rate-limit calls to any service that requires it.
ExRated is:
You can learn more about the concept for this rate limiter in the Token Bucket article on Wikipedia
If you use the PhoenixFramework there is also a great blog post on Rate Limiting a Phoenix API by danielberkompas describing how to write a plug to use ExRated in your own API. Its fast and its easy.
Call the ExRated application with ExRated.check_rate/3
. This function takes three arguments:
bucket name
(Erlang term, typically String). You can have as many buckets as you need.scale
(Integer). The time scale in milliseconds that the bucket is valid for.limit
(Integer). How many actions you want to limit your app to in the time scale provided.For example, if you have to enforce a rate limit of no more than 5 calls in 10 seconds to your API:
iex> ExRated.check_rate("my-rate-limited-api", 10_000, 5)
{:ok, 1}
The ExRated.check_rate
function will return an {:ok, Integer}
tuple if its OK to proceed with your rate limited function. The Integer returned is the current value of the incrementing counter showing how many times in the time scale window your function has already been called. If you are over limit a {:error, Integer}
tuple will be returned where the Integer is always the limit you have specified in the function call.
Call the ExRated application with ExRated.inspect_bucket/3
. This function takes the same three arguments as check_rate
:
For example, if you want to inspect the bucket for your API:
iex> ExRated.inspect_bucket("my-rate-limited-api", 10_000, 5)
{0, 5, 2483, nil, nil}
iex> ExRated.check_rate("my-rate-limited-api", 10_000, 5)
{:ok, 1}
iex> ExRated.inspect_bucket("my-rate-limited-api", 10_000, 5)
{1, 4, 723, 1450282268397, 1450282268397}
The ExRated.inspect_bucket
function will return a {count, count_remaining, ms_to_next_bucket, created_at, updated_at}
tuple, count and count_remaining are integers, ms_to_next_bucket is the number of milliseconds before the bucket resets, created_at and updated_at are timestamps in milliseconds.
Call the ExRated application with ExRated.delete_bucket/1
. This function takes one argument:
bucket name
(String). You can have as many buckets as you need.For example, if you want to reset the counter for your API:
iex> ExRated.delete_bucket("my-rate-limited-api")
:ok
The ExRated.delete_bucket
function will return an :ok
on success or :error
if the bucket doesn't exist
You can use ExRated in your projects in two steps:
Add ExRated to your mix.exs
dependencies:
def deps do
[{:ex_rated, "~> 2.0"}]
end
List :ex_rated
in your application dependencies:
def application do
[applications: [:ex_rated]]
end
You can also start the GenServer manually, and pass it custom config, with something like:
{:ok, pid} = GenServer.start_link(ExRated, [ {:timeout, 10_000}, {:cleanup_rate, 10_000}, {:persistent, false} ], [name: :ex_rated])
Alternatively, you can configure them in your config/config.exs
(or
other config) file like
config :ex_rated,
timeout: 10_000,
cleanup_rate: 10_000,
persistent: false,
name: :ex_rated,
ets_table_name: :ets_rated_test_buckets
These args and their defaults are:
{:timeout, 90_000_000}
: buckets older than this in milliseconds will be automatically pruned.
{:cleanup_rate, 60_000}
: how often, in milliseconds, the bucket pruning process will be run.
{:ets_table_name, :ex_rated_buckets}
: The atom name of the ETS
table. This can be configured within your config
files but not when
starting the GenServer manually.
{:persistent, false}
: Whether to persist ETS table to disk with DETS on server stop/restart.
[name: :ex_rated]
: The registered name of the ExRated GenServer.
Please run the following commands before pushing a pull request to ensure your code has been properly formatted and static analysis run.
mix format
mix credo --strict
It is important that the OTP doesn't get automatically started by Mix.
mix test --no-start
You can use the Benchfella
library to do a quick performance test.
On a 2019 Macbook Pro (2.3 GHz 8-Core Intel Core i9, 64GB RAM) the lib can do 10,000,000 checks in less than 10s, averaging 0.89 µs/op (microseconds).
$ mix bench
Compiling 1 file (.ex)
Settings:
duration: 1.0 s
## BasicBench
[10:45:54] 1/1: Basic Bench
Finished in 9.87 seconds
## BasicBench
benchmark na iterations average time
Basic Bench 10000000 0.89 µs/op
Supervisor.Spec.worker
usage. [@jechol]init/1
from generated docs. [@jechol]ets_table_name
if overriding.ex_doc
and ex2ms
dependencies._
prefix unused variables to avoid compilation warnings.ets_table_name()
warning: function timestamp/1 is unused
. [@brianberlin]ex2ms
to v1.5Supervisor.Spec.worker
fun [@walkr]ex2ms
to v1.4{:persistent, false}
option to server config to allow persisting data to disk.delete_bucket/1
function. Takes a bucket name and removes it now instead of waiting for pruning (Nick Sanders).inspect_bucket/3
function. Returns metadata about buckets (Nick Sanders).:erlang.system_time(:milli_seconds)
provided by the new Time API in OTP 18 and greater if available, and will fall back gracefully to the old :erlang.now()
in older versions. Thanks to Mitchell Henke (mitchellhenke) for the enhancement.ExRated source code is released under Apache 2 License. Check LICENSE file for more information.