Track failed proxy urls and don't request them again

CHANGELOG.md

@@ -117,6 +117,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - Mastodon API: Added an endpoint to get multiple statuses by IDs (`GET /api/v1/statuses/?ids[]=1&ids[]=2`)
 - ActivityPub: Add ActivityPub actor's `discoverable` parameter.
 - Admin API: Added moderation log filters (user/start date/end date/search/pagination)
+- Reverse Proxy: Do not retry failed requests to limit pressure on the peer
 
 ### Changed
 - Configuration: Filter.AnonymizeFilename added ability to retain file extension with custom text

lib/pleroma/application.ex

@@ -102,7 +102,8 @@ defp cachex_children do
       build_cachex("scrubber", limit: 2500),
       build_cachex("idempotency", expiration: idempotency_expiration(), limit: 2500),
       build_cachex("web_resp", limit: 2500),
-      build_cachex("emoji_packs", expiration: emoji_packs_expiration(), limit: 10)
+      build_cachex("emoji_packs", expiration: emoji_packs_expiration(), limit: 10),
+      build_cachex("failed_proxy_url", limit: 2500)
     ]
   end
 

lib/pleroma/reverse_proxy/reverse_proxy.ex

@@ -15,6 +15,7 @@ defmodule Pleroma.ReverseProxy do
   @valid_resp_codes [200, 206, 304]
   @max_read_duration :timer.seconds(30)
   @max_body_length :infinity
+  @failed_request_ttl :timer.seconds(60)
   @methods ~w(GET HEAD)
 
   @moduledoc """
@@ -48,6 +49,8 @@ defmodule Pleroma.ReverseProxy do
   * `max_read_duration` (default `#{inspect(@max_read_duration)}` ms): the total time the connection is allowed to
   read from the remote upstream.
 
+  * `failed_request_ttl` (default `#{inspect(@failed_request_ttl)}` ms): the time the failed request is cached and cannot be retried.
+
   * `inline_content_types`:
     * `true` will not alter `content-disposition` (up to the upstream),
     * `false` will add `content-disposition: attachment` to any request,
@@ -83,6 +86,7 @@ defmodule Pleroma.ReverseProxy do
           {:keep_user_agent, boolean}
           | {:max_read_duration, :timer.time() | :infinity}
           | {:max_body_length, non_neg_integer() | :infinity}
+          | {:failed_request_ttl, :timer.time() | :infinity}
           | {:http, []}
           | {:req_headers, [{String.t(), String.t()}]}
           | {:resp_headers, [{String.t(), String.t()}]}
@@ -108,7 +112,8 @@ def call(conn = %{method: method}, url, opts) when method in @methods do
         opts
       end
 
-    with {:ok, code, headers, client} <- request(method, url, req_headers, hackney_opts),
+    with {:ok, nil} <- Cachex.get(:failed_proxy_url_cache, url),
+         {:ok, code, headers, client} <- request(method, url, req_headers, hackney_opts),
          :ok <-
            header_length_constraint(
              headers,
@@ -116,12 +121,18 @@ def call(conn = %{method: method}, url, opts) when method in @methods do
            ) do
       response(conn, client, url, code, headers, opts)
     else
+      {:ok, true} ->
+        conn
+        |> error_or_redirect(url, 500, "Request failed", opts)
+        |> halt()
+
       {:ok, code, headers} ->
         head_response(conn, url, code, headers, opts)
         |> halt()
 
       {:error, {:invalid_http_response, code}} ->
         Logger.error("#{__MODULE__}: request to #{inspect(url)} failed with HTTP status #{code}")
+        track_failed_url(url, code, opts)
 
         conn
         |> error_or_redirect(
@@ -134,6 +145,7 @@ def call(conn = %{method: method}, url, opts) when method in @methods do
 
       {:error, error} ->
         Logger.error("#{__MODULE__}: request to #{inspect(url)} failed: #{inspect(error)}")
+        track_failed_url(url, error, opts)
 
         conn
         |> error_or_redirect(url, 500, "Request failed", opts)
@@ -388,4 +400,17 @@ defp increase_read_duration(_) do
   end
 
   defp client, do: Pleroma.ReverseProxy.Client
+
+  defp track_failed_url(url, code, opts) do
+    code = to_string(code)
+
+    ttl =
+      if code in ["403", "404"] or String.starts_with?(code, "5") do
+        Keyword.get(opts, :failed_request_ttl, @failed_request_ttl)
+      else
+        nil
+      end
+
+    Cachex.put(:failed_proxy_url_cache, url, true, ttl: ttl)
+  end
 end

test/reverse_proxy_test.exs

@@ -42,6 +42,18 @@ defp user_agent_mock(user_agent, invokes) do
     end)
   end
 
+  describe "reverse proxy" do
+    test "do not track successful request", %{conn: conn} do
+      user_agent_mock("hackney/1.15.1", 2)
+      url = "/success"
+
+      conn = ReverseProxy.call(conn, url)
+
+      assert conn.status == 200
+      assert Cachex.get(:failed_proxy_url_cache, url) == {:ok, nil}
+    end
+  end
+
   describe "user-agent" do
     test "don't keep", %{conn: conn} do
       user_agent_mock("hackney/1.15.1", 2)
@@ -71,9 +83,15 @@ test "length returns error if content-length more than option", %{conn: conn} do
       user_agent_mock("hackney/1.15.1", 0)
 
       assert capture_log(fn ->
-               ReverseProxy.call(conn, "/user-agent", max_body_length: 4)
+               ReverseProxy.call(conn, "/huge-file", max_body_length: 4)
              end) =~
-               "[error] Elixir.Pleroma.ReverseProxy: request to \"/user-agent\" failed: :body_too_large"
+               "[error] Elixir.Pleroma.ReverseProxy: request to \"/huge-file\" failed: :body_too_large"
+
+      assert {:ok, true} == Cachex.get(:failed_proxy_url_cache, "/huge-file")
+
+      assert capture_log(fn ->
+               ReverseProxy.call(conn, "/huge-file", max_body_length: 4)
+             end) == ""
     end
 
     defp stream_mock(invokes, with_close? \\ false) do
@@ -140,28 +158,54 @@ defp error_mock(status) when is_integer(status) do
   describe "returns error on" do
     test "500", %{conn: conn} do
       error_mock(500)
+      url = "/status/500"
 
-      capture_log(fn -> ReverseProxy.call(conn, "/status/500") end) =~
+      capture_log(fn -> ReverseProxy.call(conn, url) end) =~
         "[error] Elixir.Pleroma.ReverseProxy: request to /status/500 failed with HTTP status 500"
+
+      assert Cachex.get(:failed_proxy_url_cache, url) == {:ok, true}
+
+      {:ok, ttl} = Cachex.ttl(:failed_proxy_url_cache, url)
+      assert ttl <= 60_000
     end
 
     test "400", %{conn: conn} do
       error_mock(400)
+      url = "/status/400"
 
-      capture_log(fn -> ReverseProxy.call(conn, "/status/400") end) =~
+      capture_log(fn -> ReverseProxy.call(conn, url) end) =~
         "[error] Elixir.Pleroma.ReverseProxy: request to /status/400 failed with HTTP status 400"
+
+      assert Cachex.get(:failed_proxy_url_cache, url) == {:ok, true}
+      assert Cachex.ttl(:failed_proxy_url_cache, url) == {:ok, nil}
+    end
+
+    test "403", %{conn: conn} do
+      error_mock(403)
+      url = "/status/403"
+
+      capture_log(fn ->
+        ReverseProxy.call(conn, url, failed_request_ttl: :timer.seconds(120))
+      end) =~
+        "[error] Elixir.Pleroma.ReverseProxy: request to /status/403 failed with HTTP status 403"
+
+      {:ok, ttl} = Cachex.ttl(:failed_proxy_url_cache, url)
+      assert ttl > 100_000
     end
 
     test "204", %{conn: conn} do
-      ClientMock
-      |> expect(:request, fn :get, "/status/204", _, _, _ -> {:ok, 204, [], %{}} end)
+      url = "/status/204"
+      expect(ClientMock, :request, fn :get, _url, _, _, _ -> {:ok, 204, [], %{}} end)
 
       capture_log(fn ->
-        conn = ReverseProxy.call(conn, "/status/204")
+        conn = ReverseProxy.call(conn, url)
         assert conn.resp_body == "Request failed: No Content"
         assert conn.halted
       end) =~
         "[error] Elixir.Pleroma.ReverseProxy: request to \"/status/204\" failed with HTTP status 204"
+
+      assert Cachex.get(:failed_proxy_url_cache, url) == {:ok, true}
+      assert Cachex.ttl(:failed_proxy_url_cache, url) == {:ok, nil}
     end
   end