Simple rate limiter to try GenServer and ETS
Run iex -S mix and then RateLimiter.start_link() to initialize GenServer and create the ETS table.
Then run RateLimiter.log/1 passing a string as ID, example: RateLimiter.log("user1"). This will
update the request counter for the specified ID on the ETS table.
After several requests (5 per minute by default) we'll receive {:error, :rate_limited} if we keep calling the log function.
Every 60 seconds the ETS table will be cleared, allowing another 5 requests.
iex> RateLimiter.start_link()
{:ok, #PID<0.108.0>}
iex> RateLimiter.log("user1")
:ok
iex> RateLimiter.log("user1")
:ok
iex> RateLimiter.log("user1")
:ok
iex> RateLimiter.log("user1")
:ok
iex> RateLimiter.log("user1")
:ok
iex> RateLimiter.log("user1")
{:error, :rate_limited}
iex> RateLimiter.log("user1")
{:error, :rate_limited}
iex> :ets.tab2list(:rate_limiter_requests)
[{"user1", 7}]