Proxy service not responding to Tool Calls

[aponcedeleonch]

I have deployed an MCP server in my Kubernetes cluster using ToolHive operator. If I do a port-forward from the headless service to my local host, the MCP server responds correctly. If I do a port-forward from the proxy service, the request times out.

The issue seems to be restricted only for tool calling. Listing tools works just fine.

MCP server details

• Developed in Python
• Uses streameable http as transport

apiVersion: toolhive.stacklok.dev/v1alpha1
kind: MCPServer
metadata:
  name: plotting-mcp
  namespace: toolhive-system
spec:
  image: ghcr.io/stackloklabs/plotting-mcp:latest
  transport: streamable-http
  port: 9090
  targetPort: 9090
  permissionProfile:
    type: builtin
    name: network
  resources:
    limits:
      cpu: "100m"
      memory: "128Mi"
    requests:
      cpu: "50m"
      memory: "64Mi"
  podTemplateSpec:
    spec:
      volumes:
        - name: mcp-tmp
          persistentVolumeClaim:
            claimName: mcp-plot-tmp
      containers:
        - name: mcp
          volumeMounts:
            - mountPath: /tmp
              name: mcp-tmp
              readOnly: false

Proxy Logs

When connecting to the server

From proxy service

3:59PM INF Transparent proxy: DELETE /mcp -> http://mcp-plotting-mcp-headless:9090
3:59PM INF Detected Mcp-Session-Id header: 9a0ac73fe2964a7596af156dc77fc7c5
3:59PM INF Transparent proxy: POST /mcp -> http://mcp-plotting-mcp-headless:9090
3:59PM INF Detected initialize method call for plotting-mcp
3:59PM INF Detected Mcp-Session-Id header: dee3b7b1dde34bf0bdfea9eed7f3154a
3:59PM INF Transparent proxy: POST /mcp -> http://mcp-plotting-mcp-headless:9090
3:59PM INF Transparent proxy: GET /mcp -> http://mcp-plotting-mcp-headless:9090
3:59PM INF Detected Mcp-Session-Id header: dee3b7b1dde34bf0bdfea9eed7f3154a

From headless service (MCP server)

2025-08-21 15:59:52 [info     ] Terminating session: 9a0ac73fe2964a7596af156dc77fc7c5 [mcp.server.streamable_http]
2025-08-21 15:59:52 [info     ] 10.0.3.83:45720 - "DELETE /mcp HTTP/1.1" 200 [uvicorn.access]
2025-08-21 15:59:52 [info     ] Created new transport with session ID: dee3b7b1dde34bf0bdfea9eed7f3154a [mcp.server.streamable_http_manager]

When listing tools

From proxy service

4:00PM INF Transparent proxy: POST /mcp -> http://mcp-plotting-mcp-headless:9090
4:00PM INF Detected Mcp-Session-Id header: dee3b7b1dde34bf0bdfea9eed7f3154a

From headless service (MCP server)

2025-08-21 16:00:26 [info     ] 10.0.3.83:41870 - "POST /mcp HTTP/1.1" 200 [uvicorn.access]
2025-08-21 16:00:26 [info     ] Processing request of type ListToolsRequest [mcp.server.lowlevel.server]

When trying to run a tool

From proxy service

4:02PM INF Transparent proxy: POST /mcp -> http://mcp-plotting-mcp-headless:9090
4:02PM INF Detected Mcp-Session-Id header: dee3b7b1dde34bf0bdfea9eed7f3154a

From headless service (MCP server)

2025-08-21 16:02:53 [info     ] 10.0.3.83:57756 - "GET / HTTP/1.1" 200 [uvicorn.access]
2025-08-21 16:02:55 [info     ] 10.0.3.83:57770 - "POST /mcp HTTP/1.1" 200 [uvicorn.access]
2025-08-21 16:02:55 [info     ] Processing request of type CallToolRequest [mcp.server.lowlevel.server]
2025-08-21 16:02:55 [info     ] Plot generated successfully    [plotting_mcp.server] kwargs={} plot_type=line size=30.9KiB