# Source: https://upstash.com/docs/workflow/basics/caveats.md

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# Caveats

## Introduction

In this guide, we'll look at best practices and caveats for using Upstash Workflow.

## Core Principles

### Execute business logic in `context.run`

Your workflow endpoint will be called multiple times during a workflow run. Therefore:

* Place your business logic code inside the `context.run` function for each step
* Code outside `context.run` only serves to connect steps

Example:

<CodeGroup>
  ```typescript api/workflow/route.ts theme={"system"}
  export const { POST } = serve<string>(async (context) => {
    const input = context.requestPayload

    const result = await context.run("step-1", () => {
      return { success: true }
    })

    console.log("This log will appear multiple times")

    await context.run("step-2", () => {
      console.log("This log will appear just once")
      console.log("Step 1 status is:", result.success)
    })
  })
  ```

  ```python main.py theme={"system"}
  @serve.post("/api/example")
  async def example(context: AsyncWorkflowContext[str]) -> None:
      input = context.request_payload

      async def _step_1() -> Dict:
          return {"success": True}

      result = await context.run("step-1", _step_1)

      print("This log will appear multiple times")

      async def _step_2() -> None:
          print("This log will appear just once")
          print("Step 1 status is:", result["success"])

      await context.run("step-2", _step_2)

  ```
</CodeGroup>

### Return Results from context.run for Later Use

Always return step results if needed in subsequent steps.

<CodeGroup>
  ```typescript ❌ Incorrect - TypeScript theme={"system"}
  export const { POST } = serve<string>(async (context) => {
    const input = context.requestPayload

    let result

    await context.run("step-1", async () => {
      result = await someWork(input)
    })
    await context.run("step-2", async () => {
      await someOtherWork(result)
    })
  })
  ```

  ```typescript ✅ Correct - TypeScript theme={"system"}
  export const { POST } = serve<string>(async (context) => {
    const input = context.requestPayload

    const result = await context.run("step-1", async () => {
      return await someWork(input)
    })

    await context.run("step-2", async () => {
      someOtherWork(result)
    })
  })
  ```

  ```python ❌ Incorrect - Python theme={"system"}
  @serve.post("/api/example")
  async def example(context: AsyncWorkflowContext[str]) -> None:
      input = context.request_payload

      result = None

      async def _step_1() -> Dict:
          nonlocal result
          result = await some_work(input)

      await context.run("step-1", _step_1)

      async def _step_2() -> None:
          await some_other_work(result)

      await context.run("step-2", _step_2)

  ```

  ```python ✅ Correct - Python theme={"system"}
  @serve.post("/api/example")
  async def example(context: AsyncWorkflowContext[str]) -> None:
      input = context.request_payload

      async def _step_1() -> Dict:
          return await some_work(input)

      result = await context.run("step-1", _step_1)

      async def _step_2() -> None:
          await some_other_work(result)

      await context.run("step-2", _step_2)

  ```
</CodeGroup>

Because your workflow endpoint is called multiple times, `result` will be unitialized when the endpoint is called again to run `step-2`.

If you are curious about why an endpoint is called multiple times, see [how Workflow works](/workflow/basics/how).

## Avoiding Common Pitfalls

### Avoid Non-deterministic Code Outside `context.run`

A workflow endpoint should always produce the same results, even if it's called multiple times. Avoid:

* Non-idempotent functions
* Time-dependent code
* Randomness

Example of what to avoid:

<CodeGroup>
  ```typescript ❌ Non-idempotent functions - TypeScript theme={"system"}
  export const { POST } = serve<{ entryId: string }>(async (context) => {
    const { entryId } = context.requestPayload;

    // 👇 Problem: Non-idempotent function outside context.run:
    const result = await getResultFromDb(entryId);
    if (result.return) {
      return;
    }

    // ...
  })
  ```

  ```typescript ❌ Time-dependent code - TypeScript theme={"system"}
  export const { POST } = serve<string>(async (context) => {
    const input = context.requestPayload

    // 👇 Problem: time-dependent code
    if (Date.now() % 5 == 2) {
      await context.run("step-1", () => {
        // ...
      })
    } else {
      await context.run("step-2", () => {
        // ...
      })
    }
  })
  ```

  ```typescript ❌ Random code - TypeScript theme={"system"}
  export const { POST } = serve<string>(async (context) => {
    const input = context.requestPayload

    // 👇 Problem: random code
    if (Math.floor(Math.random() * 10) % 5 == 2) {
      await context.run("step-1", () => {
        // ...
      })
    } else {
      await context.run("step-2", () => {
        // ...
      })
    }
  })
  ```

  ```python ❌ Non-idempotent functions - Python theme={"system"}
  @serve.post("/api/example")
  async def example(context: AsyncWorkflowContext[str]) -> None:
      entry_id = context.request_payload["entry_id"]

      # 👇 Problem: Non-idempotent function outside context.run:
      result = await get_result_from_db(entry_id)
      if result.should_return:
          return

      # ...

  ```

  ```python ❌ Time-dependent code - Python theme={"system"}
  @serve.post("/api/example")
  async def example(context: AsyncWorkflowContext[str]) -> None:
      input = context.request_payload

      # 👇 Problem: time-dependent code
      if time.time() % 5 == 2:
          await context.run("step-1", lambda: ...)
      else:
          await context.run("step-2", lambda: ...)

  ```

  ```python ❌ Random code - Python theme={"system"}
  @serve.post("/api/example")
  async def example(context: AsyncWorkflowContext[str]) -> None:
      input = context.request_payload

      # 👇 Problem: random code
      if random.randint(0, 9) % 5 == 2:
          await context.run("step-1", lambda: ...)
      else:
          await context.run("step-2", lambda: ...)

  ```
</CodeGroup>

If you implement a non-idempotent code like the one shown above, you might encounter `Failed to authenticate Workflow request.` errors. This can happen if you `return` based on the result of the non-idempotent code before any workflow step.

To prevent this, ensure that the non-idempotent code (such as `getResultFromDb` in the example) runs within `context.run`.

<CodeGroup>
  ```typescript TypeScript theme={"system"}
  const result = await context.run(async () => {
    await getResultFromDb(entryId)
  });
  if (result.return) {
    return;
  }
  ```

  ```python Python theme={"system"}
  async def _get_result_from_db():
      return await get_result_from_db(entry_id)

  result = await context.run("get-result-from-db", _get_result_from_db)

  if result.should_return:
      return

  ```
</CodeGroup>

### Ensure Idempotency in `context.run`

Business logic should be idempotent due to potential retries in distributed systems. In other words, **when a workflow runs twice with the same input, the end result should be the same as if the workflow only ran once**.

In the example below, the `someWork` function must be idempotent:

<CodeGroup>
  ```typescript api/workflow/route.ts theme={"system"}
  export const { POST } = serve<string>(async (context) => {
    const input = context.requestPayload

    await context.run("step-1", async () => {
      return someWork(input)
    })
  })
  ```

  ```python main.py theme={"system"}
  @serve.post("/api/example")
  async def example(context: AsyncWorkflowContext[str]) -> None:
      input = context.request_payload

      async def _step_1() -> None:
          return await some_work(input)

      await context.run("step-1", _step_1)

  ```
</CodeGroup>

Imagine that `someWork` executes once and makes a change to a database. However, before the database had a chance to respond with the successful change, the connection is lost. Your Workflow cannot know if the database change was successful or not. The caller has no choice but to retry, which will cause `someWork` to run twice.

If `someWork` is not idempotent, this could lead to unintended consequences. For example duplicated records or corrupted data. Idempotency is crucial to maintaining the integrity and reliability of your workflow.

### Don't Nest Context Methods

Avoid calling `context.call`, `context.sleep`, `context.sleepFor`, or `context.run` within another `context.run`.

<CodeGroup>
  ```typescript api/workflow/route.ts theme={"system"}
  import { serve } from "@upstash/workflow/nextjs"

  export const { POST } = serve<string>(async (context) => {
    const input = context.requestPayload

    await context.run("step-1", async () => {
      await context.sleep(...) // ❌ INCORRECT
      await context.run(...) // ❌ INCORRECT
      await context.call(...) // ❌ INCORRECT
    })
  })
  ```

  ```python main.py theme={"system"}
  @serve.post("/api/example")
  async def example(context: AsyncWorkflowContext[str]) -> None:
      input = context.request_payload

      async def _step_1() -> None:
          await context.sleep(...) #  ❌ INCORRECT
          await context.run(...) #  ❌ INCORRECT
          await context.call(...) #  ❌ INCORRECT

      await context.run("step-1", _step_1)

  ```
</CodeGroup>

### Include At Least One Step in Workflow

Every workflow must include at least one step execution with `context.run`. If no steps are defined, the workflow will throw a `Failed to authenticate Workflow request.` error.

<CodeGroup>
  ```typescript ❌ Missing steps - TypeScript theme={"system"}
  export const { POST } = serve<string>(async (context) => {
    const input = context.requestPayload
    
    // 👇 Problem: No context.run call
    console.log("Processing input:", input)
    
    // This workflow will fail with "Failed to authenticate Workflow request."
  })
  ```

  ```typescript ✅ Correct - TypeScript theme={"system"}
  export const { POST } = serve<string>(async (context) => {
    const input = context.requestPayload
    
    // 👇 At least one step is required
    await context.run("dummy-step", async () => {
      return
    })
  })
  ```

  ```python ❌ Missing steps - Python theme={"system"}
  @serve.post("/api/example")
  async def example(context: AsyncWorkflowContext[str]) -> None:
      input = context.request_payload
      
      # 👇 Problem: No context.run call
      print("Processing input:", input)
      
      # This workflow will fail with "Failed to authenticate Workflow request."
  ```

  ```python ✅ Correct - Python theme={"system"}
  @serve.post("/api/example")
  async def example(context: AsyncWorkflowContext[str]) -> None:
      input = context.request_payload
      
      # 👇 At least one step is required
      async def _dummy_step():
          return
          
      await context.run("dummy-step", _dummy_step)
  ```
</CodeGroup>

Even for the placeholder implementations, you must include one dummy step for the Workflow authentication mechanism to function properly.

### Avoid Promise.any

In workflow-js, you can use [`Promise.all` to run steps in parallel](/workflow/howto/parallel-runs). However, a similar method, [`Promise.any`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/any), is not supported for workflow steps.

While `Promise.all` works seamlessly, `Promise.any` does not currently function with workflow steps. We are exploring the possibility of adding support for `Promise.any` in the future.

If you have a specific use case that requires `Promise.any`, don't hesitate to reach out to Upstash support.