RuntimeError: Received request before initialization was complete

[WhenGrill]

Hi,

I am encountering an error RuntimeError: Received request before initialization was complete. It happens 9 out of 10 times when running in docker.

I am using Cursor IDE v0.49.5 with Remote SSH connection. As per Cursor's MCP Docs I am running the MCP server on my machine locally not on the remote machine. From my local machine the MCP server is connecting to database which resides on external host. Using <EXTERNAL-HOST> as IP address or Domain Name does not make a difference.

---

EDIT - Observations:

• When Cursor is open, even though no Chat is currently generating, it will always request "GET /sse HTTP/1.1" 200 OK right after I run the server.
• When I close Cursor, run MCP server, re-open Cursor everything seems to be working fine.
• This pottentially implies, that MCP server did not have much time to intialize after startup, thus breaking the functionality until you restart the server.

---

Docker-Compose:

services:
  postgres-mcp:
    container_name: mcp-postgres
    image: crystaldba/postgres-mcp:0.2.1
    ports:
      - "8000:8000"
    environment:
      - DATABASE_URI=postgresql://postgres:changeme@<EXTERNAL-HOST>:5432/<DB-NAME>
    command: ["--access-mode=restricted", "--transport=sse"]

Cursor MCP Settings:

{
  "mcpServers": {
      "postgres": {
          "type": "sse",
          "url": "http://localhost:8000/sse"
      }
  }
}

Error Message in docker logs:

SSE transport detected, adding --sse-host=0.0.0.0
----------------
Executing command:
postgres-mcp --access-mode=restricted --transport=sse --sse-host=0.0.0.0
----------------
[04/27/25 05:36:08] INFO     Starting PostgreSQL MCP Server in     server.py:537
                             RESTRICTED mode
                    INFO     Successfully connected to database    server.py:550
                             and initialized connection pool
INFO:     Started server process [7]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Uvicorn running on http://0.0.0.0:8000 (Press CTRL+C to quit)
INFO:     192.168.0.1:48052 - "GET /sse HTTP/1.1" 200 OK
INFO:     192.168.0.1:50832 - "POST /messages/?session_id=7bb8cfacba994332a57ccee9505af0e3 HTTP/1.1" 202 Accepted
ERROR:    Exception in ASGI application
  + Exception Group Traceback (most recent call last):
  |   File "/app/.venv/lib/python3.12/site-packages/uvicorn/protocols/http/h11_impl.py", line 403, in run_asgi
  |     result = await app(  # type: ignore[func-returns-value]
  |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |   File "/app/.venv/lib/python3.12/site-packages/uvicorn/middleware/proxy_headers.py", line 60, in __call__
  |     return await self.app(scope, receive, send)
  |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |   File "/app/.venv/lib/python3.12/site-packages/starlette/applications.py", line 112, in __call__
  |     await self.middleware_stack(scope, receive, send)
  |   File "/app/.venv/lib/python3.12/site-packages/starlette/middleware/errors.py", line 187, in __call__
  |     raise exc
  |   File "/app/.venv/lib/python3.12/site-packages/starlette/middleware/errors.py", line 165, in __call__
  |     await self.app(scope, receive, _send)
  |   File "/app/.venv/lib/python3.12/site-packages/starlette/middleware/exceptions.py", line 62, in __call__
  |     await wrap_app_handling_exceptions(self.app, conn)(scope, receive, send)
  |   File "/app/.venv/lib/python3.12/site-packages/starlette/_exception_handler.py", line 53, in wrapped_app
  |     raise exc
  |   File "/app/.venv/lib/python3.12/site-packages/starlette/_exception_handler.py", line 42, in wrapped_app
  |     await app(scope, receive, sender)
  |   File "/app/.venv/lib/python3.12/site-packages/starlette/routing.py", line 714, in __call__
  |     await self.middleware_stack(scope, receive, send)
  |   File "/app/.venv/lib/python3.12/site-packages/starlette/routing.py", line 734, in app
  |     await route.handle(scope, receive, send)
  |   File "/app/.venv/lib/python3.12/site-packages/starlette/routing.py", line 288, in handle
  |     await self.app(scope, receive, send)
  |   File "/app/.venv/lib/python3.12/site-packages/starlette/routing.py", line 76, in app
  |     await wrap_app_handling_exceptions(app, request)(scope, receive, send)
  |   File "/app/.venv/lib/python3.12/site-packages/starlette/_exception_handler.py", line 53, in wrapped_app
  |     raise exc
  |   File "/app/.venv/lib/python3.12/site-packages/starlette/_exception_handler.py", line 42, in wrapped_app
  |     await app(scope, receive, sender)
  |   File "/app/.venv/lib/python3.12/site-packages/starlette/routing.py", line 73, in app
  |     response = await f(request)
  |                ^^^^^^^^^^^^^^^^
  |   File "/app/.venv/lib/python3.12/site-packages/mcp/server/fastmcp/server.py", line 485, in handle_sse
  |     async with sse.connect_sse(
  |                ^^^^^^^^^^^^^^^^
  |   File "/usr/local/lib/python3.12/contextlib.py", line 231, in __aexit__
  |     await self.gen.athrow(value)
  |   File "/app/.venv/lib/python3.12/site-packages/mcp/server/sse.py", line 123, in connect_sse
  |     async with anyio.create_task_group() as tg:
  |                ^^^^^^^^^^^^^^^^^^^^^^^^^
  |   File "/app/.venv/lib/python3.12/site-packages/anyio/_backends/_asyncio.py", line 772, in __aexit__
  |     raise BaseExceptionGroup(
  | ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
  +-+---------------- 1 ----------------
    | Exception Group Traceback (most recent call last):
    |   File "/app/.venv/lib/python3.12/site-packages/mcp/server/sse.py", line 131, in connect_sse
    |     yield (read_stream, write_stream)
    |   File "/app/.venv/lib/python3.12/site-packages/mcp/server/fastmcp/server.py", line 490, in handle_sse
    |     await self._mcp_server.run(
    |   File "/app/.venv/lib/python3.12/site-packages/mcp/server/lowlevel/server.py", line 483, in run
    |     async with AsyncExitStack() as stack:
    |                ^^^^^^^^^^^^^^^^
    |   File "/usr/local/lib/python3.12/contextlib.py", line 754, in __aexit__
    |     raise exc_details[1]
    |   File "/usr/local/lib/python3.12/contextlib.py", line 737, in __aexit__
    |     cb_suppress = await cb(*exc_details)
    |                   ^^^^^^^^^^^^^^^^^^^^^^
    |   File "/app/.venv/lib/python3.12/site-packages/mcp/shared/session.py", line 210, in __aexit__
    |     return await self._task_group.__aexit__(exc_type, exc_val, exc_tb)
    |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |   File "/app/.venv/lib/python3.12/site-packages/anyio/_backends/_asyncio.py", line 772, in __aexit__
    |     raise BaseExceptionGroup(
    | ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
    +-+---------------- 1 ----------------
      | Traceback (most recent call last):
      |   File "/app/.venv/lib/python3.12/site-packages/mcp/shared/session.py", line 324, in _receive_loop
      |     await self._received_request(responder)
      |   File "/app/.venv/lib/python3.12/site-packages/mcp/server/session.py", line 163, in _received_request
      |     raise RuntimeError(
      | RuntimeError: Received request before initialization was complete
      +------------------------------------
INFO:     192.168.0.1:50834 - "GET /sse HTTP/1.1" 200 OK