Durable Execution concepts

Durable execution uses the same concepts for both workflows and endpoints. Learn the concepts before exploring how to build with Inngest.

Example

A payment may need approval before your app can charge a card. Inngest can start the work now, pause it while approval is pending, and continue it later. The original server process does not need to continue running while the function pauses.

Every durable function has the following pattern: trigger → run → steps → result.

Base concepts

• Function: Either a workflow or endpoint that runs a series of steps.
• Trigger: How a function starts. This may be an event, a schedule, an HTTP request, or an invocation through the REST API.
• Steps: Units of work whose outputs Inngest saves. A run can continue after a failed step without repeating completed steps.
  • Waits: A step can wait until a time or another event. Waits suspend the function's compute and do not count toward concurrency.
• Memoization: Serializing and storing a step output for use when the function replays.
• Idempotency: An operation that has the same effect when repeated, such as a payment request that does not charge the card twice.
• Expressions: CEL conditions that can add logic to triggers and waits.
• Results: The data that a function returns and Inngest stores as its result.
• Flow control: Rules for if and when functions run, such as concurrency, throttling, rate limiting, and debounce.
• Errors vs failures: Inngest can retry errors. A step or function fails if every retry results in an error.

Additional concepts

• Apps: An app is a service that serves a set of functions.
• Syncs: You register an app and its functions with Inngest so it knows which functions run for each trigger.
• Traces: Show the path a function takes across steps, waits, retries, and the result.
• Lifecycles: A function transitions from queued to running to resolved, either completed or failed. Lifecycles run for each status transition.

Follow the quick start to see these concepts in a working function.

See a durable workflow

This example shows a workflow: an event starts background work, a step saves a result, and a wait pauses the run. Durable Endpoints apply the same step model to an HTTP request.

The parts of a workflow

The code

Each snippet defines a process-task function triggered by app/task.created. The step returns the task ID, then the run pauses for one second before returning a result. The snippets assume you have created an Inngest client; the quick starts show client setup and how to serve the function.

export const processTask = inngest.createFunction(
  { id: "process-task", triggers: { event: "app/task.created" } },
  async ({ event, step }) => {
    const result = await step.run("handle-task", () => ({
      processed: true,
      id: event.data.id,
    }));

    await step.sleep("pause", "1s");
    return result;
  }
);

Inngest saves the handle-task result. If later work retries, the SDK returns that result instead of running the completed callback again. The one-second sleep pauses the run without keeping a process open. Code outside a step can run again when the function replays, so keep external side effects in steps and make retried operations safe to repeat.

What you can build

Explore both durable function types

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