ReqFuse

ReqFuse on Github https://github.com/carsdotcom/req_fuse

ReqFuse on Hex https://hex.pm/packages/req_fuse

ReqFuse on HexDocs https://hexdocs.pm/req_fuse

Req plugin for :fuse

ReqFuse provides circuit-breaker (or load-shedding) functionality for HTTP requests that use the Req library.

Usage

After adding the dependencies, simply attach the ReqFuse step to your request ensuring you are passing in the required and any optional fuse configuration.

Mix.install([
  {:req, "~> 0.3"},
  {:req_fuse, "~> 0.3"}
])

req_fuse_opts = [fuse_name: My.Example.Fuse]
req = [url: "https://httpstat.us/500", retry: :never]
|> Req.new()
|> ReqFuse.attach(req_fuse_opts)

# Fire the request enough times to melt the fuse
Enum.each(0..10, fn _ -> Req.request(req) end)
  => :ok
Req.request(req)
  => 08:45:42.518 [warning] :fuse circuit breaker is open; fuse = Elixir.My.Example.Fuse
  => {:error, %RuntimeError{message: "circuit breaker is open"}}

Installation

If available in Hex, the package can be installed by adding req_fuse to your list of dependencies in mix.exs:

def deps do
  [
    {:req_fuse, ">= 0.3.0"}
  ]
end

Twiddling the Knobs

Attach the circuit-breaker :fuse step and configure the available options

Fuse Options

• :fuse_melt_func - A 1-arity function to determine if response should melt the fuse defaults to ReqFuse.Steps.Fuse.melt?/1
• :fuse_mode - how to query the fuse, which has two values:
  • :sync - queries are serialized through the :fuse_server process (the default)
  • :async_dirty - queries check the fuse state directly, but may not account for recent melts or resets
• :fuse_name - REQUIRED the name of the fuse to install
• :fuse_opts The fuse strategy options (see fuse docs for reference) (order matters) See ReqFuse.Steps.Fuse.defaults/0 for more information.
• :fuse_verbose - If false, suppress Log output

See https://github.com/jlouis/fuse#tutorial for more information about the supported fuse strategies and their options.

See also the additional discussion on options in ReqFuse.Steps.Fuse

Telemetry

ReqFuse emits telemetry events for observability:

Events

• [:req_fuse, :blown] - Emitted when a request is blocked because the fuse is blown (circuit breaker is open).

Metadata

• :fuse_name - The name of the fuse that is blown.

Example Handler

:telemetry.attach(
  "req-fuse-handler",
  [:req_fuse, :blown],
  fn _event, _measurements, metadata, _config ->
    Logger.warning("Circuit breaker open for #{inspect(metadata.fuse_name)}")
  end,
  nil
)

License

See LICENSE

Updates

See CHANGELOG.md

Updating the changelog. (Uses auto-changelog) https://github.com/cookpete/auto-changelog

auto-changelog --breaking-pattern "BREAKING CHANGE" --template keepachangelog --commit-limit false --unreleased

Tagging by version in mix.exs

  git tag `grep -e '@version \"\d\.\d\.\d\".*' mix.exs | awk '{gsub(/"/, "", $2); print $2}'`