feat: add hammer rate limiter

config/config.exs

@@ -39,6 +39,10 @@ config :logger, :console,
 # Use Jason for JSON parsing in Phoenix
 config :phoenix, :json_library, Jason
 
+# Use ETS as backend, expires keys every 60 seconds, cleans up expired entries every 60 seconds
+config :hammer,
+  backend: {Hammer.Backend.ETS, [expiry_ms: 60_000, cleanup_interval_ms: 60_000]}
+
 # Import environment specific config. This must remain at the bottom
 # of this file so it overrides the configuration defined above.
 import_config "#{config_env()}.exs"

lib/atlas/application.ex

@@ -17,7 +17,9 @@ defmodule Atlas.Application do
       # Start a worker by calling: Atlas.Worker.start_link(arg)
       # {Atlas.Worker, arg},
       # Start to serve requests, typically the last entry
-      AtlasWeb.Endpoint
+      AtlasWeb.Endpoint,
+      # Start Hammer in Supervision Tree
+      {Hammer.Backend.ETS, [expiry_ms: 60_000, cleanup_interval_ms: 60_000]}
     ]
 
     # See https://hexdocs.pm/elixir/Supervisor.html

lib/atlas_web/plugs/rate_limiter.ex

@@ -0,0 +1,49 @@
+defmodule AtlasWeb.Plugs.RateLimiter do
+  @moduledoc """
+  A Plug for rate limiting requests by IP address and user ID using Hammer.
+
+  ## How It Works
+
+  - Limits **IP addresses** to `# {@ip_limit}` requests per `# {@interval}` ms.
+  - Limits **authenticated users** (via `conn.assigns[:current_user_id]`) to `# {@user_limit}` requests per `# {@interval}` ms.
+  - If either limit is exceeded, the request is halted with a `429 Too Many Requests` response.
+
+  This plug expects `conn.assigns[:current_user_id]` to be set by an authentication plug earlier in the pipeline.
+  If not present, the plug will default to treating the user as `"anon"`.
+  """
+
+  import Plug.Conn
+  alias Hammer
+
+  @ip_limit 100
+  @user_limit 60
+  @interval 60_000
+
+  def init(opts), do: opts
+
+  def call(conn, _opts) do
+    ip = conn.remote_ip |> Tuple.to_list() |> Enum.join(".")
+    user_id = get_user_id(conn)
+
+    with {:ok, true} <- check_rate("ip:#{ip}", @ip_limit),
+         {:ok, true} <- check_rate("user:#{user_id}", @user_limit) do
+      conn
+    else
+      {:error, :rate_limited} ->
+        conn
+        |> send_resp(429, "Rate limit exceeded")
+        |> halt()
+    end
+  end
+
+  defp check_rate(key, limit) do
+    case Hammer.check_rate(key, @interval, limit) do
+      {:allow, _count} -> {:ok, true}
+      {:deny, _limit} -> {:error, :rate_limited}
+    end
+  end
+
+  defp get_user_id(conn) do
+    conn.assigns[:current_user_id] || "anon"
+  end
+end

lib/atlas_web/router.ex

@@ -3,6 +3,7 @@ defmodule AtlasWeb.Router do
 
   pipeline :api do
     plug :accepts, ["json"]
+    plug AtlasWeb.Plugs.RateLimiter
   end
 
   scope "/api", AtlasWeb do

mix.exs

@@ -55,7 +55,10 @@ defmodule Atlas.MixProject do
 
       # server
       {:dns_cluster, "~> 0.1.1"},
-      {:bandit, "~> 1.2"}
+      {:bandit, "~> 1.2"},
+
+      # rate limiting
+      {:hammer, "~> 6.2.1"}
     ]
   end
 

mix.lock

@@ -10,6 +10,7 @@
   "ecto_sql": {:hex, :ecto_sql, "3.13.2", "a07d2461d84107b3d037097c822ffdd36ed69d1cf7c0f70e12a3d1decf04e2e1", [:mix], [{:db_connection, "~> 2.4.1 or ~> 2.5", [hex: :db_connection, repo: "hexpm", optional: false]}, {:ecto, "~> 3.13.0", [hex: :ecto, repo: "hexpm", optional: false]}, {:myxql, "~> 0.7", [hex: :myxql, repo: "hexpm", optional: true]}, {:postgrex, "~> 0.19 or ~> 1.0", [hex: :postgrex, repo: "hexpm", optional: true]}, {:tds, "~> 2.1.1 or ~> 2.2", [hex: :tds, repo: "hexpm", optional: true]}, {:telemetry, "~> 0.4.0 or ~> 1.0", [hex: :telemetry, repo: "hexpm", optional: false]}], "hexpm", "539274ab0ecf1a0078a6a72ef3465629e4d6018a3028095dc90f60a19c371717"},
   "file_system": {:hex, :file_system, "1.1.0", "08d232062284546c6c34426997dd7ef6ec9f8bbd090eb91780283c9016840e8f", [:mix], [], "hexpm", "bfcf81244f416871f2a2e15c1b515287faa5db9c6bcf290222206d120b3d43f6"},
   "finch": {:hex, :finch, "0.19.0", "c644641491ea854fc5c1bbaef36bfc764e3f08e7185e1f084e35e0672241b76d", [:mix], [{:mime, "~> 1.0 or ~> 2.0", [hex: :mime, repo: "hexpm", optional: false]}, {:mint, "~> 1.6.2 or ~> 1.7", [hex: :mint, repo: "hexpm", optional: false]}, {:nimble_options, "~> 0.4 or ~> 1.0", [hex: :nimble_options, repo: "hexpm", optional: false]}, {:nimble_pool, "~> 1.1", [hex: :nimble_pool, repo: "hexpm", optional: false]}, {:telemetry, "~> 0.4 or ~> 1.0", [hex: :telemetry, repo: "hexpm", optional: false]}], "hexpm", "fc5324ce209125d1e2fa0fcd2634601c52a787aff1cd33ee833664a5af4ea2b6"},
+  "hammer": {:hex, :hammer, "6.2.1", "5ae9c33e3dceaeb42de0db46bf505bd9c35f259c8defb03390cd7556fea67ee2", [:mix], [{:poolboy, "~> 1.5", [hex: :poolboy, repo: "hexpm", optional: false]}], "hexpm", "b9476d0c13883d2dc0cc72e786bac6ac28911fba7cc2e04b70ce6a6d9c4b2bdc"},
   "hpax": {:hex, :hpax, "1.0.3", "ed67ef51ad4df91e75cc6a1494f851850c0bd98ebc0be6e81b026e765ee535aa", [:mix], [], "hexpm", "8eab6e1cfa8d5918c2ce4ba43588e894af35dbd8e91e6e55c817bca5847df34a"},
   "jason": {:hex, :jason, "1.4.4", "b9226785a9aa77b6857ca22832cffa5d5011a667207eb2a0ad56adb5db443b8a", [:mix], [{:decimal, "~> 1.0 or ~> 2.0", [hex: :decimal, repo: "hexpm", optional: true]}], "hexpm", "c5eb0cab91f094599f94d55bc63409236a8ec69a21a67814529e8d5f6cc90b3b"},
   "mime": {:hex, :mime, "2.0.7", "b8d739037be7cd402aee1ba0306edfdef982687ee7e9859bee6198c1e7e2f128", [:mix], [], "hexpm", "6171188e399ee16023ffc5b76ce445eb6d9672e2e241d2df6050f3c771e80ccd"},
@@ -25,6 +26,7 @@
   "phoenix_template": {:hex, :phoenix_template, "1.0.4", "e2092c132f3b5e5b2d49c96695342eb36d0ed514c5b252a77048d5969330d639", [:mix], [{:phoenix_html, "~> 2.14.2 or ~> 3.0 or ~> 4.0", [hex: :phoenix_html, repo: "hexpm", optional: true]}], "hexpm", "2c0c81f0e5c6753faf5cca2f229c9709919aba34fab866d3bc05060c9c444206"},
   "plug": {:hex, :plug, "1.18.0", "d78df36c41f7e798f2edf1f33e1727eae438e9dd5d809a9997c463a108244042", [:mix], [{:mime, "~> 1.0 or ~> 2.0", [hex: :mime, repo: "hexpm", optional: false]}, {:plug_crypto, "~> 1.1.1 or ~> 1.2 or ~> 2.0", [hex: :plug_crypto, repo: "hexpm", optional: false]}, {:telemetry, "~> 0.4.3 or ~> 1.0", [hex: :telemetry, repo: "hexpm", optional: false]}], "hexpm", "819f9e176d51e44dc38132e132fe0accaf6767eab7f0303431e404da8476cfa2"},
   "plug_crypto": {:hex, :plug_crypto, "2.1.1", "19bda8184399cb24afa10be734f84a16ea0a2bc65054e23a62bb10f06bc89491", [:mix], [], "hexpm", "6470bce6ffe41c8bd497612ffde1a7e4af67f36a15eea5f921af71cf3e11247c"},
+  "poolboy": {:hex, :poolboy, "1.5.2", "392b007a1693a64540cead79830443abf5762f5d30cf50bc95cb2c1aaafa006b", [:rebar3], [], "hexpm", "dad79704ce5440f3d5a3681c8590b9dc25d1a561e8f5a9c995281012860901e3"},
   "postgrex": {:hex, :postgrex, "0.20.0", "363ed03ab4757f6bc47942eff7720640795eb557e1935951c1626f0d303a3aed", [:mix], [{:db_connection, "~> 2.1", [hex: :db_connection, repo: "hexpm", optional: false]}, {:decimal, "~> 1.5 or ~> 2.0", [hex: :decimal, repo: "hexpm", optional: false]}, {:jason, "~> 1.0", [hex: :jason, repo: "hexpm", optional: true]}, {:table, "~> 0.1.0", [hex: :table, repo: "hexpm", optional: true]}], "hexpm", "d36ef8b36f323d29505314f704e21a1a038e2dc387c6409ee0cd24144e187c0f"},
   "swoosh": {:hex, :swoosh, "1.19.3", "02ad4455939f502386e4e1443d4de94c514995fd0e51b3cafffd6bd270ffe81c", [:mix], [{:bandit, ">= 1.0.0", [hex: :bandit, repo: "hexpm", optional: true]}, {:cowboy, "~> 1.1 or ~> 2.4", [hex: :cowboy, repo: "hexpm", optional: true]}, {:ex_aws, "~> 2.1", [hex: :ex_aws, repo: "hexpm", optional: true]}, {:finch, "~> 0.6", [hex: :finch, repo: "hexpm", optional: true]}, {:gen_smtp, "~> 0.13 or ~> 1.0", [hex: :gen_smtp, repo: "hexpm", optional: true]}, {:hackney, "~> 1.9", [hex: :hackney, repo: "hexpm", optional: true]}, {:jason, "~> 1.0", [hex: :jason, repo: "hexpm", optional: false]}, {:mail, "~> 0.2", [hex: :mail, repo: "hexpm", optional: true]}, {:mime, "~> 1.1 or ~> 2.0", [hex: :mime, repo: "hexpm", optional: false]}, {:mua, "~> 0.2.3", [hex: :mua, repo: "hexpm", optional: true]}, {:multipart, "~> 0.4", [hex: :multipart, repo: "hexpm", optional: true]}, {:plug, "~> 1.9", [hex: :plug, repo: "hexpm", optional: true]}, {:plug_cowboy, ">= 1.0.0", [hex: :plug_cowboy, repo: "hexpm", optional: true]}, {:req, "~> 0.5.10 or ~> 0.6 or ~> 1.0", [hex: :req, repo: "hexpm", optional: true]}, {:telemetry, "~> 0.4.2 or ~> 1.0", [hex: :telemetry, repo: "hexpm", optional: false]}], "hexpm", "04a10f8496786b744b84130e3510eb53ca51e769c39511b65023bdf4136b732f"},
   "telemetry": {:hex, :telemetry, "1.3.0", "fedebbae410d715cf8e7062c96a1ef32ec22e764197f70cda73d82778d61e7a2", [:rebar3], [], "hexpm", "7015fc8919dbe63764f4b4b87a95b7c0996bd539e0d499be6ec9d7f3875b79e6"},