Temporalex

Workflow orchestration for Elixir, built on the Temporal Core SDK (Rust) over Rustler NIFs.

Temporalex workflows read top-to-bottom as sequential code. Concurrency is explicit and structured — there is no implicit event loop. The runtime uses a deterministic cooperative scheduler that owns thread ordering, so command sequences are reproducible from the same activation transcript regardless of BEAM scheduling or mailbox timing.

Status: 0.3.0. This release is an architectural rewrite around a deterministic core, a Temporalex.Backend boundary that isolates Temporal Core / Rust details, and structured concurrency primitives phase and parallel. The 0.x line is not backwards-compatible with 0.2.0. See CHANGELOG.md for the migration notes.

Core design and scheduler authored by @hansihe; see docs/scheduler_and_replay.md and docs/implementation_principles.md.

Install

# mix.exs
defp deps do
  [{:temporalex, "~> 0.3.0"}]
end

Requirements: Elixir ~> 1.17, Rust toolchain (the NIF crate compiles on first build against temporalio/sdk-rust v0.4.0).

Run a Temporal dev server

brew install temporal
temporal server start-dev

The Web UI lands at http://localhost:8233; the gRPC endpoint at localhost:7233.

Define an activity

defmodule MyApp.Activities.Payment do
  use Temporalex.Activity

  defactivity charge(amount), start_to_close_timeout: 30_000 do
    {:ok, "charge-#{amount}"}
  end

  # Local activity: runs in-process on the same worker, durable via a
  # history marker. Use for short, deterministic work where the network
  # round-trip to schedule a regular activity isn't worth it.
  defactivity stamp(prefix), local: true, start_to_close_timeout: 5_000 do
    {:ok, "#{prefix}-#{System.unique_integer([:positive])}"}
  end
end

Structured errors

Activities can raise Temporalex.ApplicationError (or return {:error, reason}); the workflow sees a typed exception with the cause preserved:

defactivity charge(amount) do
  if amount > 10_000 do
    raise %Temporalex.ApplicationError{
      message: "amount exceeds limit",
      type: "AmountTooLarge",
      non_retryable: true
    }
  else
    {:ok, amount}
  end
end

# In the workflow:
case Activities.charge(amount) do
  {:ok, charge}                                                    -> ...
  {:error, %Temporalex.ActivityFailure{cause: %{type: "AmountTooLarge"}}} -> ...
end

Define a workflow

defmodule MyApp.Workflows.Checkout do
  use Temporalex.Workflow

  alias Temporalex.Workflow.API

  def handle_query("status", _args, state), do: {:reply, state}

  def run(args) do
    API.publish_state(:charging)
    {:ok, charge} = MyApp.Activities.Payment.charge(args["amount"])

    API.publish_state(:awaiting_confirmation)

    confirmed =
      API.phase(false,
        signal: %{
          "confirm" => fn _args, _state -> {:stop, true} end,
          "cancel"  => fn _args, _state -> {:stop, false} end
        },
        timeout: :timer.minutes(5)
      )

    case confirmed do
      {:timeout, _state} -> {:error, :timed_out}
      true               -> {:ok, %{charge: charge, confirmed: true}}
      false              -> {:error, :user_cancelled}
    end
  end
end

Start a worker

children = [
  {Temporalex.Worker,
   name: MyApp.Temporal,
   backend: Temporalex.Backend.TemporalCore,
   target: "http://127.0.0.1:7233",
   namespace: "default",
   task_queue: "checkout",
   workflows: [MyApp.Workflows.Checkout],
   activities: [MyApp.Activities.Payment],
   # :etf (default) preserves full Elixir term fidelity.
   # :json makes payloads renderable by `temporal` CLI and non-Elixir
   # clients, at the cost of lossy term encoding (atoms → strings,
   # tuples → unsupported).
   payload_codec: :etf}
]

Supervisor.start_link(children, strategy: :one_for_one)

Metrics

Temporal's core records worker-side metrics — poller counts, slot usage, and schedule_to_start latency, which is the signal you autoscale workers on. They are off by default. The exporter belongs to the runtime, so it is configured on the client:

{Temporalex.Client,
 name: MyApp.Temporal,
 backend: Temporalex.Backend.TemporalCore,
 target: "http://127.0.0.1:7233",
 namespace: "default",
 telemetry: [
   prometheus: [bind_address: "0.0.0.0:9464"],
   global_tags: %{"service" => "checkout-worker", "env" => "prod"}
 ]}

GET /metrics on that address then serves, among others:

temporal_num_pollers
temporal_worker_task_slots_available
temporal_worker_task_slots_used
temporal_workflow_task_schedule_to_start_latency
temporal_workflow_task_execution_latency
temporal_workflow_endtoend_latency
temporal_workflow_completed

For OTLP instead — to an OpenTelemetry Collector, or any agent with an OTLP intake:

telemetry: [
  otlp: [
    url: "http://localhost:4317",
    protocol: :grpc,                  # or :http
    metric_temporality: :cumulative,  # or :delta
    metric_periodicity_ms: 1_000,
    headers: %{"authorization" => "Bearer ..."}
  ]
]

:prometheus and :otlp are mutually exclusive on one runtime. Other keys: metric_prefix (default "temporal_"), attach_service_name, and durations_as_seconds.

Build id

Workers report a build id, which lands on every WorkflowTaskCompleted event and so answers "which release executed this task?" from history or the Web UI:

{Temporalex.Worker,
 name: MyApp.Temporal,
 client: MyApp.TemporalClient,
 task_queue: "checkout",
 build_id: System.get_env("BUILD_ID", "dev"),
 workflows: [MyApp.Workflows.Checkout]}

This is identification only — worker versioning is not enabled, so the build id does not affect task routing. Defaults to "temporalex-<version>".

Drive workflows from a client

{:ok, handle} =
  Temporalex.Client.start_workflow(
    MyApp.Temporal,
    MyApp.Workflows.Checkout,
    %{"amount" => 100},
    workflow_id: "checkout-#{order_id}"
  )

:ok = Temporalex.Client.signal_workflow(handle, "confirm")
{:ok, status} = Temporalex.Client.query_workflow(handle, "status")
{:ok, result} = Temporalex.Client.get_result(handle)

The full client surface: start_workflow, get_result, signal_workflow, query_workflow, update_workflow, cancel_workflow, terminate_workflow, describe_workflow.

Programming model

Workflows are a single run/1 function. Concurrency enters only through phase and parallel, which act as structured concurrency scopes — every async handler spawned within a scope must complete before the scope returns.

Full details, return-value contracts, and the determinism rationale:

• docs/programming_model.md — public workflow programming model
• docs/scheduler_and_replay.md — scheduler rounds, pause points, replay matching
• docs/implementation_principles.md — internal invariants and admission rules
• docs/sdk_overview.md — architecture map

Testing

Temporalex.Backend.Test is an in-memory backend that lets you drive a worker with core activation structs directly — no Temporal server required. The same Temporalex.Server and Temporalex.Core.Executor that handle real traffic also handle the test backend, so workflow code under test runs the production codepath.

start_supervised!(
  {Temporalex.Worker,
   name: MyApp.Temporal,
   backend: Temporalex.Backend.Test,
   workflows: [MyApp.Workflows.Checkout],
   activities: [MyApp.Activities.Payment]}
)

See test/temporalex/server_integration_test.exs for full activation and activity-task transcripts.

Project layout

lib/temporalex/
  workflow.ex                use Temporalex.Workflow
  workflow/api.ex            sequential primitives, phase, parallel
  activity.ex                defactivity macro
  activity/context.ex        heartbeat, cancelled? for activity bodies
  client.ex                  start / get_result / signal / query / update / cancel / terminate / describe
  worker.ex                  Supervisor — what users add to their tree
  server.ex                  Worker server: backend state, executor registry, activation routing
  core/executor.ex           deterministic workflow executor (scheduler + replay)
  core/structs.ex            internal protocol: Activation, Job, Command, Completion, Op
  core/test_harness.ex       in-process harness for testing the core directly
  backend.ex                 Backend behaviour
  backend/test.ex            in-memory backend for tests
  backend/temporal_core.ex   Rustler-backed Temporal Core backend
  native.ex                  Rustler NIF surface (do not call directly)
native/temporalex_nif/
  src/                       Rust NIF crate

Contributing

The architecture is documented in docs/. Start with docs/sdk_overview.md. The docs/implementation_principles.md admission rule applies to any new workflow API: a primitive only enters the public surface if it has a precise replay contract and can be tested without the real Temporal backend.

Run the quality gates before committing — CI enforces all four:

mix format
mix test
mix credo --strict
mix dialyzer

Credo is configured in .credo.exs. The few relaxations (Temporal-style exception names, NIF stub arities) are commented in the config; individually exempted functions carry credo:disable-for-next-line comments at the site explaining why.

License

MIT — see LICENSE.