Remote MCP endpoint returns 404 because Docker image likely omits MCP dependencies

[paulieb89]

Summary

The deployed remote MCP endpoint at https://property-shared.fly.dev/mcp is returning 404 when invoked by ChatGPT/MCP tooling.

This does not appear to be a /mcp vs /sse path issue. The repo and FastMCP defaults both indicate /mcp is the correct Streamable HTTP endpoint.

Observed behavior

Attempting to call the deployed MCP tool endpoint fails with:

MCP SSE probe returned 404 from fly.dev
url: https://property-shared.fly.dev/mcp
status_code: 404

Relevant repo findings

README advertises /mcp

README.md says:

Remote server deployed at `https://property-shared.fly.dev/mcp` (Streamable HTTP).

FastAPI app expects to mount MCP at /mcp

app/main.py contains:

from property_mcp.server import mcp as mcp_server
_mcp_app = mcp_server.http_app(path="/mcp")

and then adds middleware to route /mcp and /mcp/* directly, avoiding Starlette's trailing-slash 307 redirect.

ImportError is silently swallowed

_setup_mcp() currently does:

try:
    from property_mcp.server import mcp as mcp_server
    _mcp_app = mcp_server.http_app(path="/mcp")
except ImportError:
    pass

If property_mcp or fastmcp is missing in the deployed image, _mcp_app remains None, the MCP middleware is not installed, and /mcp returns 404.

Docker image appears to omit MCP dependencies/package

Dockerfile installs only the API extra:

RUN uv sync --frozen --no-dev --extra api

and copies only:

COPY app ./app
COPY property_core ./property_core

But app/main.py imports property_mcp.server, and pyproject.toml does not list property_mcp in the packaged folders. fastmcp[apps]==3.2.4 is under the apps extra, not the api extra.

Likely root cause

The Fly deployment starts the FastAPI app successfully, but the optional MCP setup fails due to missing MCP dependencies/package. Because the ImportError is swallowed, the deployment appears healthy while /mcp is never registered.

Proposed fix

1. Ensure the deploy image installs the MCP dependencies, for example:

RUN uv sync --frozen --no-dev --extra api --extra apps

2. Ensure the MCP package is actually present in the image. Either copy the package:

COPY property_mcp ./property_mcp

or add the correct published MCP package dependency to the deployed extras.

3. Log or fail loudly when MCP is expected but unavailable:

def _setup_mcp() -> None:
    global _mcp_app
    try:
        from property_mcp.server import mcp as mcp_server

        _mcp_app = mcp_server.http_app(
            path="/mcp",
            transport="streamable-http",
            stateless_http=True,
        )
    except ImportError as exc:
        import logging
        logging.getLogger(__name__).exception("MCP disabled: %s", exc)

4. Optional: add a lightweight smoke test/check for /mcp after deployment, so this class of failure is caught before publishing the endpoint.

Notes

fly.toml sets:

FASTMCP_STATELESS_HTTP = "true"

So Streamable HTTP on /mcp is the appropriate target. Classic SSE at /sse is probably not the right endpoint for this deployment mode.