open-webui/open-webui · error · HTTPException

[ERROR: Failed to connect to the image generation engine]

Error message

[ERROR: Failed to connect to the image generation engine]

What it means

Raised while resolving the default model when IMAGE_GENERATION_ENGINE is 'automatic1111' (or empty): the code GETs {AUTOMATIC1111_BASE_URL}/sdapi/v1/options and any exception — connection refused, timeout, bad JSON, missing 'sd_model_checkpoint' key — becomes HTTP 400 'Failed to connect to the image generation engine' (images.py:214-222).

Source

Thrown at backend/open_webui/routers/images.py:222

    if image_config.IMAGE_GENERATION_ENGINE == 'openai':
        return image_config.IMAGE_GENERATION_MODEL if image_config.IMAGE_GENERATION_MODEL else 'dall-e-2'
    elif image_config.IMAGE_GENERATION_ENGINE == 'gemini':
        return image_config.IMAGE_GENERATION_MODEL if image_config.IMAGE_GENERATION_MODEL else 'imagen-3.0-generate-002'
    elif image_config.IMAGE_GENERATION_ENGINE == 'comfyui':
        return image_config.IMAGE_GENERATION_MODEL if image_config.IMAGE_GENERATION_MODEL else ''
    elif image_config.IMAGE_GENERATION_ENGINE == 'automatic1111' or image_config.IMAGE_GENERATION_ENGINE == '':
        try:
            session = await get_session()
            async with session.get(
                url=f'{image_config.AUTOMATIC1111_BASE_URL}/sdapi/v1/options',
                headers={'authorization': get_automatic1111_api_auth(image_config)},
                ssl=AIOHTTP_CLIENT_SESSION_SSL,
            ) as r:
                options = await r.json()
            return options['sd_model_checkpoint']
        except Exception as e:
            log.exception(f'Failed to get default model from automatic1111: {e}')
            raise HTTPException(
                status_code=400,
                detail=ERROR_MESSAGES.DEFAULT(e, 'Failed to connect to the image generation engine'),
            )


class ImagesConfig(BaseModel):
    ENABLE_IMAGE_GENERATION: bool
    ENABLE_IMAGE_PROMPT_GENERATION: bool

    IMAGE_GENERATION_ENGINE: str
    IMAGE_GENERATION_MODEL: str
    IMAGE_SIZE: str | None
    IMAGE_STEPS: int | None

    IMAGES_OPENAI_API_BASE_URL: str
    IMAGES_OPENAI_API_KEY: str
    IMAGES_OPENAI_API_VERSION: str
    IMAGES_OPENAI_API_PARAMS: dict | str | None

View on GitHub (pinned to 01f4282f1f)

Solutions

curl {AUTOMATIC1111_BASE_URL}/sdapi/v1/options from the Open WebUI host — it must return JSON containing sd_model_checkpoint
Restart Automatic1111 with --api (and --listen if remote) and fix AUTOMATIC1111_BASE_URL in Admin Settings > Images
For HTTPS with self-signed certs, configure the trusted CA via AIOHTTP_CLIENT_SESSION_SSL / persistent_config rather than disabling checks broadly
If the key is missing, upgrade the A1111 API version or pin an engine/model explicitly so the checkpoint lookup is skipped

Example fix

# before: wrong base URL
AUTOMATIC1111_BASE_URL=http://localhost:7860/
# A1111 actually listening on 0.0.0.0:7861 with --api
# after
AUTOMATIC1111_BASE_URL=http://a1111-host:7861/
# launch: python launch.py --api --listen --port 7861

Defensive patterns

Strategy: try-catch

Validate before calling

import httpx, os

async def a1111_alive(base_url: str) -> bool:
    try:
        r = await httpx.get(f'{base_url}/sdapi/v1/options', timeout=5)
        return r.status_code == 200 and 'sd_model_checkpoint' in r.json()
    except Exception:
        return False

Try / catch

try:
    model = await client.get('/api/v1/images/config')  # any path resolving the A1111 checkpoint
except httpx.HTTPStatusError as e:
    if 'Failed to connect to the image generation engine' in e.response.text:
        raise RuntimeError('Automatic1111 unreachable: check AUTOMATIC1111_BASE_URL and --api flag')
    raise

Prevention

Start A1111 with --api and verify /sdapi/v1/options before saving image config
Health-check the engine URL from the Open WebUI host/container, not your browser
Keep AUTOMATIC1111_BASE_URL in sync when the engine moves (host, port, TLS)

When it happens

Trigger: Any admin config/image-model request that resolves the A1111 checkpoint while the Automatic1111 (stable-diffusion-webui) API is down, AUTOMATIC1111_BASE_URL is wrong (missing http://, wrong port, or pointing at the UI instead of the --api endpoint), TLS verification fails, or the response lacks sd_model_checkpoint because the API version is old.

Common situations: A1111 launched without the --api flag; base URL left at default after moving the service; self-signed HTTPS with AIOHTTP_CLIENT_SESSION_SSL rejecting it; A1111 updated and changed its options schema.

Related errors

AI-assisted analysis of open-webui/open-webui@01f4282f1f (2026-08-14). Data as JSON: /api/errors/901d66c7b1d65f64. Report an issue: GitHub.