fix: memory leak in session removal - close MCP server properly (#471)

- Add close() method to N8NDocumentationMCPServer that:
  - Calls server.close() (MCP SDK cleanup)
  - Clears internal cache
  - Nullifies service references to help GC
- Update removeSession() to call server.close() before releasing references

Root cause: removeSession() deleted server from map but didn't call cleanup
Evidence: Production server memory grew ~1GB in 43 minutes (10% to 35%)

Conceived by Romuald Członkowski - https://www.aiadvisors.pl/en

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

CHANGELOG.md

@@ -7,6 +7,31 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [2.28.7] - 2025-12-05
+
+### Bug Fixes
+
+**Memory Leak: MCP Server Cleanup on Session Removal (#471)**
+
+Fixed memory leak where `N8NDocumentationMCPServer` objects were not properly closed when sessions were removed, causing memory growth over time.
+
+- **Root Cause**: `removeSession()` deleted server from map but didn't call cleanup methods
+- **Evidence**: Production server memory grew from ~10% to ~35% in 43 minutes (~1GB growth with 4GB container)
+
+- **Solution**:
+  - Added `close()` method to `N8NDocumentationMCPServer` that:
+    - Calls `server.close()` (MCP SDK cleanup)
+    - Calls `cache.destroy()` to stop cleanup timer and clear entries
+    - Closes database connection properly
+    - Nullifies service references to help GC
+  - Updated `removeSession()` to call `server.close()` before releasing references
+
+- **Files Changed**:
+  - `src/mcp/server.ts` - Added `close()` method
+  - `src/http-server-single-session.ts` - Call `server.close()` in `removeSession()`
+
+**Conceived by Romuald Członkowski - [AiAdvisors](https://www.aiadvisors.pl/en)**
+
 ## [2.28.6] - 2025-12-05
 
 ### Bug Fixes

dist/http-server-single-session.d.ts.map

@@ -1 +1 @@
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+{"version":3,"file":"http-server-single-session.d.ts","sourceRoot":"","sources":["../src/http-server-single-session.ts"],"names":[],"mappings":";AAMA,OAAO,OAAO,MAAM,SAAS,CAAC;AAoB9B,OAAO,EAAE,eAAe,EAA2B,MAAM,0BAA0B,CAAC;AACpF,OAAO,EAAE,YAAY,EAAE,MAAM,uBAAuB,CAAC;AAuErD,qBAAa,uBAAuB;IAElC,OAAO,CAAC,UAAU,CAA8D;IAChF,OAAO,CAAC,OAAO,CAA0D;IACzE,OAAO,CAAC,eAAe,CAAsE;IAC7F,OAAO,CAAC,eAAe,CAA4D;IACnF,OAAO,CAAC,kBAAkB,CAAyC;IACnE,OAAO,CAAC,OAAO,CAAwB;IACvC,OAAO,CAAC,cAAc,CAAwB;IAC9C,OAAO,CAAC,aAAa,CAAM;IAC3B,OAAO,CAAC,cAAc,CAAkB;IACxC,OAAO,CAAC,SAAS,CAAuB;IACxC,OAAO,CAAC,YAAY,CAA+B;;IAcnD,OAAO,CAAC,mBAAmB;IAmB3B,OAAO,CAAC,sBAAsB;YAqChB,aAAa;IAkC3B,OAAO,CAAC,qBAAqB;IAO7B,OAAO,CAAC,gBAAgB;IAkBxB,OAAO,CAAC,gBAAgB;IASxB,OAAO,CAAC,sBAAsB;IAkC9B,OAAO,CAAC,mBAAmB;YASb,oBAAoB;YAwBpB,oBAAoB;IAwBlC,OAAO,CAAC,iBAAiB;IAsBzB,OAAO,CAAC,aAAa;IA2BrB,OAAO,CAAC,mBAAmB;IAoDrB,aAAa,CACjB,GAAG,EAAE,OAAO,CAAC,OAAO,EACpB,GAAG,EAAE,OAAO,CAAC,QAAQ,EACrB,eAAe,CAAC,EAAE,eAAe,GAChC,OAAO,CAAC,IAAI,CAAC;YAmOF,eAAe;IA8C7B,OAAO,CAAC,SAAS;IAYjB,OAAO,CAAC,gBAAgB;IASlB,KAAK,IAAI,OAAO,CAAC,IAAI,CAAC;IAgnBtB,QAAQ,IAAI,OAAO,CAAC,IAAI,CAAC;IAkD/B,cAAc,IAAI;QAChB,MAAM,EAAE,OAAO,CAAC;QAChB,SAAS,CAAC,EAAE,MAAM,CAAC;QACnB,GAAG,CAAC,EAAE,MAAM,CAAC;QACb,QAAQ,CAAC,EAAE;YACT,KAAK,EAAE,MAAM,CAAC;YACd,MAAM,EAAE,MAAM,CAAC;YACf,OAAO,EAAE,MAAM,CAAC;YAChB,GAAG,EAAE,MAAM,CAAC;YACZ,UAAU,EAAE,MAAM,EAAE,CAAC;SACtB,CAAC;KACH;IAmDM,kBAAkB,IAAI,YAAY,EAAE;IAoEpC,mBAAmB,CAAC,QAAQ,EAAE,YAAY,EAAE,GAAG,MAAM;CAsG7D"}

dist/http-server-single-session.js

@@ -101,10 +101,14 @@ class SingleSessionHTTPServer {
     async removeSession(sessionId, reason) {
         try {
             const transport = this.transports[sessionId];
+            const server = this.servers[sessionId];
             delete this.transports[sessionId];
             delete this.servers[sessionId];
             delete this.sessionMetadata[sessionId];
             delete this.sessionContexts[sessionId];
+            if (server) {
+                await server.close();
+            }
             if (transport) {
                 await transport.close();
             }

dist/mcp/server.d.ts

@@ -14,6 +14,7 @@ export declare class N8NDocumentationMCPServer {
     private earlyLogger;
     private disabledToolsCache;
     constructor(instanceContext?: InstanceContext, earlyLogger?: EarlyErrorLogger);
+    close(): Promise<void>;
     private initializeDatabase;
     private initializeInMemorySchema;
     private parseSQLStatements;

dist/mcp/server.d.ts.map

@@ -1 +1 @@
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+{"version":3,"file":"server.d.ts","sourceRoot":"","sources":["../../src/mcp/server.ts"],"names":[],"mappings":"AAsCA,OAAO,EAAE,eAAe,EAAE,MAAM,2BAA2B,CAAC;AAE5D,OAAO,EAAE,gBAAgB,EAAE,MAAM,iCAAiC,CAAC;AAkFnE,qBAAa,yBAAyB;IACpC,OAAO,CAAC,MAAM,CAAS;IACvB,OAAO,CAAC,EAAE,CAAgC;IAC1C,OAAO,CAAC,UAAU,CAA+B;IACjD,OAAO,CAAC,eAAe,CAAgC;IACvD,OAAO,CAAC,WAAW,CAAgB;IACnC,OAAO,CAAC,KAAK,CAAqB;IAClC,OAAO,CAAC,UAAU,CAAa;IAC/B,OAAO,CAAC,eAAe,CAAC,CAAkB;IAC1C,OAAO,CAAC,YAAY,CAAuB;IAC3C,OAAO,CAAC,qBAAqB,CAAsB;IACnD,OAAO,CAAC,WAAW,CAAiC;IACpD,OAAO,CAAC,kBAAkB,CAA4B;gBAE1C,eAAe,CAAC,EAAE,eAAe,EAAE,WAAW,CAAC,EAAE,gBAAgB;IA2FvE,KAAK,IAAI,OAAO,CAAC,IAAI,CAAC;YAed,kBAAkB;YAwClB,wBAAwB;IA0BtC,OAAO,CAAC,kBAAkB;YA6CZ,iBAAiB;IAa/B,OAAO,CAAC,eAAe,CAAkB;YAE3B,sBAAsB;IAgDpC,OAAO,CAAC,gBAAgB;IAqCxB,OAAO,CAAC,aAAa;IAoTrB,OAAO,CAAC,wBAAwB;IAoFhC,OAAO,CAAC,kBAAkB;IAqE1B,OAAO,CAAC,uBAAuB;IAwB/B,OAAO,CAAC,qBAAqB;YAgTf,SAAS;YA2DT,WAAW;YA0EX,WAAW;YAyCX,cAAc;YAyKd,gBAAgB;IAqD9B,OAAO,CAAC,mBAAmB;IAwE3B,OAAO,CAAC,eAAe;YAsBT,eAAe;IAqI7B,OAAO,CAAC,kBAAkB;IAQ1B,OAAO,CAAC,uBAAuB;IA0D/B,OAAO,CAAC,iBAAiB;YAqFX,WAAW;YAgCX,oBAAoB;YA2EpB,qBAAqB;YAwDrB,iBAAiB;YA2JjB,OAAO;YAgDP,cAAc;YAgFd,iBAAiB;IAqC/B,OAAO,CAAC,iBAAiB;IA0BzB,OAAO,CAAC,iBAAiB;IA0BzB,OAAO,CAAC,eAAe;IAwCvB,OAAO,CAAC,kBAAkB;IAiC1B,OAAO,CAAC,aAAa;IAoCrB,OAAO,CAAC,0BAA0B;IAgClC,OAAO,CAAC,4BAA4B;YAKtB,oBAAoB;IAsDlC,OAAO,CAAC,gBAAgB;YAiBV,SAAS;YA6CT,kBAAkB;YA+DlB,uBAAuB;YAsDvB,iBAAiB;IAqE/B,OAAO,CAAC,qBAAqB;IA8C7B,OAAO,CAAC,uBAAuB;IAwD/B,OAAO,CAAC,iBAAiB;YAoDX,mBAAmB;YAkGnB,qBAAqB;IAS7B,OAAO,CAAC,SAAS,EAAE,GAAG,GAAG,OAAO,CAAC,IAAI,CAAC;YAS9B,aAAa;YAcb,iBAAiB;YAoBjB,WAAW;YAwBX,eAAe;YAqBf,mBAAmB;YAwBnB,yBAAyB;IA4CvC,OAAO,CAAC,kBAAkB;YAiBZ,gBAAgB;YA6HhB,2BAA2B;YAiE3B,2BAA2B;IAyEnC,GAAG,IAAI,OAAO,CAAC,IAAI,CAAC;IA0BpB,QAAQ,IAAI,OAAO,CAAC,IAAI,CAAC;CAuBhC"}

dist/mcp/server.js

@@ -147,6 +147,19 @@ class N8NDocumentationMCPServer {
         });
         this.setupHandlers();
     }
+    async close() {
+        try {
+            await this.server.close();
+            this.cache.clear();
+            this.db = null;
+            this.repository = null;
+            this.templateService = null;
+            this.earlyLogger = null;
+        }
+        catch (error) {
+            logger_1.logger.warn('Error closing MCP server', { error: error instanceof Error ? error.message : String(error) });
+        }
+    }
     async initializeDatabase(dbPath) {
         try {
             if (this.earlyLogger) {

package.json

@@ -1,6 +1,6 @@
 {
   "name": "n8n-mcp",
-  "version": "2.28.6",
+  "version": "2.28.7",
   "description": "Integration between n8n workflow automation and Model Context Protocol (MCP)",
   "main": "dist/index.js",
   "types": "dist/index.d.ts",

package.runtime.json

@@ -1,6 +1,6 @@
 {
   "name": "n8n-mcp-runtime",
-  "version": "2.28.0",
+  "version": "2.28.7",
   "description": "n8n MCP Server Runtime Dependencies Only",
   "private": true,
   "dependencies": {

src/http-server-single-session.ts

@@ -180,17 +180,29 @@ export class SingleSessionHTTPServer {
    */
   private async removeSession(sessionId: string, reason: string): Promise<void> {
     try {
-      // Store reference to transport before deletion
+      // Store references before deletion
       const transport = this.transports[sessionId];
+      const server = this.servers[sessionId];
 
-      // Delete transport FIRST to prevent onclose handler from triggering recursion
+      // Delete references FIRST to prevent onclose handler from triggering recursion
       // This breaks the circular reference: removeSession -> close -> onclose -> removeSession
       delete this.transports[sessionId];
       delete this.servers[sessionId];
       delete this.sessionMetadata[sessionId];
       delete this.sessionContexts[sessionId];
 
-      // Close transport AFTER deletion
+      // Close server first (may have references to transport)
+      // This fixes memory leak where server resources weren't freed (issue #471)
+      // Handle server close errors separately so transport close still runs
+      if (server && typeof server.close === 'function') {
+        try {
+          await server.close();
+        } catch (serverError) {
+          logger.warn('Error closing server', { sessionId, error: serverError });
+        }
+      }
+
+      // Close transport last
       // When onclose handler fires, it won't find the transport anymore
       if (transport) {
         await transport.close();

src/mcp/server.ts

@@ -220,7 +220,46 @@ export class N8NDocumentationMCPServer {
 
     this.setupHandlers();
   }
-  
+
+  /**
+   * Close the server and release resources.
+   * Should be called when the session is being removed.
+   *
+   * Order of cleanup:
+   * 1. Close MCP server connection
+   * 2. Destroy cache (clears entries AND stops cleanup timer)
+   * 3. Close database connection
+   * 4. Null out references to help GC
+   */
+  async close(): Promise<void> {
+    try {
+      await this.server.close();
+
+      // Use destroy() not clear() - also stops the cleanup timer
+      this.cache.destroy();
+
+      // Close database connection before nullifying reference
+      if (this.db) {
+        try {
+          this.db.close();
+        } catch (dbError) {
+          logger.warn('Error closing database', {
+            error: dbError instanceof Error ? dbError.message : String(dbError)
+          });
+        }
+      }
+
+      // Null out references to help garbage collection
+      this.db = null;
+      this.repository = null;
+      this.templateService = null;
+      this.earlyLogger = null;
+    } catch (error) {
+      // Log but don't throw - cleanup should be best-effort
+      logger.warn('Error closing MCP server', { error: error instanceof Error ? error.message : String(error) });
+    }
+  }
+
   private async initializeDatabase(dbPath: string): Promise<void> {
     try {
       // Checkpoint: Database connecting (v2.18.3)