Cannot create Chatflow as MCP Tool with Docker + localhost

[naisy]

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Dify version

1.7.1

Cloud or Self Hosted

Self Hosted (Docker)

Steps to reproduce

Title

Cannot create Chatflow as MCP Tool with Docker + localhost

Version

• Dify v1.7.1
• Running on AWS EC2 with Docker (docker compose -f docker-compose.yaml -p dify up -d)

Description

My environment

• AWS EC2 instance
• Dify running via Docker Compose
• Port 80 of the EC2 instance is forwarded so that I can access Dify from my PC using localhost

The problem is: what does localhost refer to in this context?

When I enable the MCP server for a Chatflow, Dify generates a URL like:

http://localhost/mcp/server/<serverid>/mcp

When I try to add this in:
Tools → MCP → Add MCP Server (HTTP)

I get the following error:

[Errno 111] Connection refused

Cause

• This URL is passed directly to the API container.
• Inside Docker, localhost refers to the container itself, so it tries to connect to port 80 of the API container.
• The nginx container’s configuration shows MCP requests are actually routed to port 5001 on the API container:
  https://github.com/langgenius/dify/blob/1.7.1/docker/nginx/conf.d/default.conf.template#L42-L45

Solution

Use this URL instead of the generated one:

http://localhost:5001/mcp/server/<serverid>/mcp

Also add the following to the API service’s environment variables in docker-compose.yaml:

NO_PROXY: localhost

After these changes, I was able to connect successfully and call the Chatflow as an MCP tool:

Notes

This appears to be a Docker + localhost specific behavior.

✔️ Expected Behavior

When running in Docker on localhost, Dify should generate an MCP server URL with the correct host/port
(e.g., http://localhost:5001/mcp/server/<serverid>/mcp), or document that this change is required.

❌ Actual Behavior

When enabling the MCP server for a Chatflow in Docker on localhost,
Dify generates a URL like http://localhost/mcp/server/<serverid>/mcp.

When this URL is used in Tools → MCP → Add MCP Server (HTTP),
the connection fails with:

[Errno 111] Connection refused

[dosubot[bot]]

Hi @naisy! I'm Dosu and I’m helping the dify team.

This is a known Docker networking issue: inside a container, localhost refers to the container itself, not the host or other containers. When Dify generates an MCP server URL like http://localhost/mcp/server/<serverid>/mcp, it tries to connect to port 80 of the API container, which fails because MCP endpoints are actually routed to port 5001 via nginx in the Docker setup (nginx config).

Your workaround—using http://localhost:5001/mcp/server/<serverid>/mcp and setting NO_PROXY: localhost in the API service environment—works because it targets the correct port and avoids proxy issues (discussion).

Best practice is to avoid localhost or 127.0.0.1 for MCP endpoints in Docker. Use the actual network IP, host.docker.internal (on Mac/Windows), or run the MCP server as a service in the same Docker network (discussion).

Currently, Dify does not automatically generate Docker-aware MCP URLs, and documentation does not clearly cover this scenario. It would help if the docs explained this networking behavior and recommended correct MCP URL formats for Docker deployments. Your suggestion to update the docs or improve URL generation logic is spot on.

To reply, just mention @dosu.

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