Workflow endpoints

Workflows are a way to chain multiple models together to create a more complex pipeline. This allows you to create a single endpoint that can take an input and pass it through multiple models in sequence. This is useful for creating more complex models that require multiple steps, or for creating a single endpoint that can handle multiple tasks.

Workflow as an API

Workflow APIs work the same way as other model endpoints, you can simply send a request and get a response back. However, it is common for workflows to contain multiple steps and produce intermediate results, as each step contains their own response that could be relevant in your use-case.

Therefore, workflows benefit from the streaming feature, which allows you to get partial results as they are being generated.

Workflow events

The workflow API will trigger a few events during its execution, these events can be used to monitor the progress of the workflow and get intermediate results. Below are the events that you can expect from a workflow stream:

The submit event

This events is triggered every time a new step has been submitted to execution. It contains the app_id, request_id and the node_id.

{
  "type": "submit",
  "node_id": "stable_diffusion_xl",
  "app_id": "fal-ai/fast-sdxl",
  "request_id": "d778bdf4-0275-47c2-9f23-16c27041cbeb"
}

The completion event

This event is triggered upon the completion of a specific step.

{
  "type": "completion",
  "node_id": "stable_diffusion_xl",
  "output": {
    "images": [
      {
        "url": "https://fal.media/result.jpeg",
        "width": 1024,
        "height": 1024,
        "content_type": "image/jpeg"
      }
    ],
    "timings": { "inference": 2.1733 },
    "seed": 6252023,
    "has_nsfw_concepts": [false],
    "prompt": "a cute puppy"
  }
}

The output event

The output event means that the workflow has completed and the final result is ready.

{
  "type": "output",
  "output": {
    "images": [
      {
        "url": "https://fal.media/result.jpeg",
        "width": 1024,
        "height": 1024,
        "content_type": "image/jpeg"
      }
    ]
  }
}

The error event

The error event is triggered when an error occurs during the execution of a step. The error object contains the error.status with the HTTP status code, an error message as well as error.body with the underlying error serialized.

{
  "type": "error",
  "node_id": "stable_diffusion_xl",
  "message": "Error while fetching the result of the request d778bdf4-0275-47c2-9f23-16c27041cbeb",
  "error": {
    "status": 422,
    "body": {
      "detail": [
        {
          "loc": ["body", "num_images"],
          "msg": "ensure this value is less than or equal to 8",
          "type": "value_error.number.not_le",
          "ctx": { "limit_value": 8 }
        }
      ]
    }
  }
}

Example

A cool and simple example of the power of workflows is workflows/fal-ai/sdxl-sticker, which consists of three steps:

1. Generates an image using fal-ai/fast-sdxl.
2. Remove the background of the image using fal-ai/imageutils/rembg.
3. Converts the image to a sticker using fal-ai/face-to-sticker.

What could be a tedious process of running and coordinating three different models is now a single endpoint that you can call with a single request.

import * as fal from "@fal-ai/serverless-client";
 
const stream = await fal.stream("workflows/fal-ai/sdxl-sticker", {
  input: {
    prompt: "a face of a cute puppy, in the style of pixar animation",
  },
});
 
for await (const event of stream) {
  console.log("partial", event);
}
 
const result = await stream.done();
console.log("final result", result);

Type definitions

Below are the type definition in TypeScript of events that you can expect from a workflow stream:

type WorkflowBaseEvent = {
  type: "submit" | "completion" | "error" | "output";
  node_id: string;
};
 
export type WorkflowSubmitEvent = WorkflowBaseEvent & {
  type: "submit";
  app_id: string;
  request_id: string;
};
 
export type WorkflowCompletionEvent<Output = any> = WorkflowBaseEvent & {
  type: "completion";
  app_id: string;
  output: Output;
};
 
export type WorkflowDoneEvent<Output = any> = WorkflowBaseEvent & {
  type: "output";
  output: Output;
};
 
export type WorkflowErrorEvent = WorkflowBaseEvent & {
  type: "error";
  message: string;
  error: any;
};