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#25742fix(MCP Client Node): Ensure MCP connections close when MCP Client node execution ends

MCP connection leaks fixed after execution

HY
hy2850
·Apr 9, 2026

MCP connections from MCP Client and MCP Client Tool nodes now close properly, preventing resource leaks after workflow execution ends.

Workflows using MCP Client or MCP Client Tool nodes would leave network connections open indefinitely after execution completed. These leaked connections consumed memory and held ports open with no way to reclaim them until the process restarted.

The fix wraps MCP connection usage in try/finally blocks across five node files, guaranteeing client.close() runs regardless of how execution ends — whether successful, errored, or cancelled. A companion fix in the core execution engine ensures cleanup callbacks registered by nodes also run in all cases, including when execution returns early or throws an error.

In the @n8n/nodes-langchain MCP nodes and core @n8n/core execution engine, resources are now properly released at the end of every workflow run.

View Original GitHub Description

Summary

MCP connections (Streamable HTTP) created by MCP Client and MCP Client Tool nodes never close and leak because cleanup (client.close()) is either missing or isn't guaranteed on all exit paths. MCP connections persist indefinitely even after workflow execution ends, consuming memory and ports.

Two root causes fixed:

1. MCP Client node-level leaks

  • Problem: McpClient.node.ts, McpClientTool.node.ts, listSearch.ts, resourceMapping.ts, and loadOptions.ts create MCP connections but don't call client.close().
  • Fix: Wrapped connection usage in try/finally blocks, ensuring client.close() is called at the end of execution.

2. Core engine leak

  • Problem: closeFunctions (cleanup callbacks registered by nodes like MCP Client Tool) are skipped in executeNode() (workflow-execute.ts) when:
    • execute() throws an error — execution jumps past cleanup
    • execute() returns an EngineRequest — early return exits before closeFunctions run
  • Fix: Moved closeFunctions invocation into a finally block so it always runs.
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Please see https://github.com/n8n-io/n8n/issues/25740 for more details

Related Linear tickets, Github issues, and Community forum posts

https://linear.app/n8n/issue/GHC-6819 Closes https://github.com/n8n-io/n8n/issues/25740

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  • Docs updated or follow-up ticket created.
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