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MCP (Model Context Protocol) Multi-Endpoint Architecture #8

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MCP (Model Context Protocol) Multi-Endpoint Architecture#8
@renecannao

Description

@renecannao
renecannao
opened on Jan 12, 2026

MCP Multi-Endpoint Architecture

Overview

This issue documents the implementation of multiple dedicated MCP endpoints in ProxySQL, where each endpoint serves a specific purpose with its own tool handler. This architecture allows for:

  • Specialized tools per endpoint (config, query, admin, cache, observe)
  • Isolated resources (separate handlers can have separate connection pools)
  • Independent authentication (per-endpoint Bearer tokens)
  • Clear separation of concerns (each endpoint has a well-defined purpose)

Architecture Diagram

┌─────────────────────────────────────────────────────────────────────────────┐
│                              ProxySQL Process                               │
│                                                                             │
│  ┌──────────────────────────────────────────────────────────────────────┐  │
│  │                     MCP_Threads_Handler                               │  │
│  │  - Configuration variables (mcp-*)                                    │  │
│  │  - Manages 5 dedicated tool handlers                                  │  │
│  └──────────────────────────────────────────────────────────────────────┘  │
│                                    │                                        │
│                                    ▼                                        │
│  ┌──────────────────────────────────────────────────────────────────────┐  │
│  │                     ProxySQL_MCP_Server                               │  │
│  │                      (Single HTTPS Server)                            │  │
│  │                                                                       │  │
│  │  Port: mcp-port (default 6071)                                        │  │
│  │  SSL: Uses ProxySQL's certificates                                    │  │
│  └──────────────────────────────────────────────────────────────────────┘  │
│                                    │                                        │
│    ┌──────────────┬──────────────┼──────────────┬──────────────┬─────────┐  │
│    ▼              ▼              ▼              ▼              ▼         ▼  │
│ ┌────┐        ┌────┐         ┌────┐         ┌────┐         ┌────┐    ┌───┐│
│ │conf│        │obs │         │qry │         │adm │         │cach│    │cat│││
│ │TH  │        │TH  │         │TH  │         │TH  │         │TH  │    │log│││
│ └─┬──┘        └─┬──┘         └─┬──┘         └─┬──┘         └─┬──┘    └─┬─┘│
│   │             │               │               │               │        │  │
│   │             │               │               │               │        │  │
│ Tools:         Tools:         Tools:         Tools:         Tools:      │  │
│ - get_config   - list_        - list_        - admin_       - get_      │  │
│ - set_config    stats          schemas       - set_          cache      │  │
│ - reload       - show_        - list_        - reload       - set_      │  │
│ - list_vars     metrics        tables                       - invalidate│  │
│ - get_status                                               - clear     │  │
│                            - query          - show         - warm      │  │
│                            - explain        processes     - entries   │  │
│                            - sample                        │  │
│                            - catalog_*       - kill        │  │
│                                             - flush       │  │
└─────────────────────────────────────────────────────────────────────────────┘

TH = Tool Handler

Endpoint Specifications

/mcp/config - Configuration Endpoint

Purpose: Runtime configuration and management of ProxySQL

Authentication: mcp-config_endpoint_auth (Bearer token)

Tools:

Tool Description Status
get_config Get current configuration values ✅ Implemented
set_config Modify configuration values ✅ Implemented
reload_config Reload configuration from disk/memory/runtime ⚠️ Stub
list_variables List all available variables ✅ Implemented
get_status Get server status information ✅ Implemented

/mcp/observe - Observability Endpoint

Purpose: Real-time metrics, statistics, and monitoring data

Authentication: mcp-observe_endpoint_auth (Bearer token)

Tools:

Tool Description Status
list_stats List available statistics ❌ Stub
get_stats Get specific statistics ❌ Stub
show_connections Show active connections ❌ Stub
show_queries Show query statistics ❌ Stub
get_health Get health check information ❌ Stub
show_metrics Show performance metrics ❌ Stub

/mcp/query - Query Endpoint

Purpose: Safe database exploration and query execution

Authentication: mcp-query_endpoint_auth (Bearer token)

Tools:

Tool Description Status
list_schemas List databases ✅ Implemented
list_tables List tables in schema ✅ Implemented
describe_table Get table structure ✅ Implemented
get_constraints Get foreign keys and constraints ✅ Implemented
table_profile Get table statistics ✅ Implemented
column_profile Get column statistics ✅ Implemented
sample_rows Get sample data ✅ Implemented
sample_distinct Sample distinct values ✅ Implemented
run_sql_readonly Execute read-only SQL ✅ Implemented
explain_sql Explain query execution plan ✅ Implemented
suggest_joins Suggest table joins ✅ Implemented
find_reference_candidates Find foreign key references ✅ Implemented
catalog_upsert Store data in catalog ✅ Implemented
catalog_get Retrieve from catalog ✅ Implemented
catalog_search Search catalog ✅ Implemented
catalog_list List catalog entries ✅ Implemented
catalog_merge Merge catalog entries ✅ Implemented
catalog_delete Delete from catalog ✅ Implemented

/mcp/admin - Administration Endpoint

Purpose: Administrative operations

Authentication: mcp-admin_endpoint_auth (Bearer token, most restrictive)

Tools:

Tool Description Status
admin_list_users List MySQL users ❌ Stub
admin_show_processes Show running processes ❌ Stub
admin_kill_query Kill a running query ❌ Stub
admin_flush_cache Flush various caches ❌ Stub
admin_reload Reload users/servers configuration ❌ Stub

/mcp/cache - Cache Endpoint

Purpose: Query cache management

Authentication: mcp-cache_endpoint_auth (Bearer token)

Tools:

Tool Description Status
get_cache_stats Get cache statistics ❌ Stub
invalidate_cache Invalidate cache entries ❌ Stub
set_cache_ttl Set cache TTL ❌ Stub
clear_cache Clear all cache ❌ Stub
warm_cache Warm up cache with queries ❌ Stub
get_cache_entries List cached queries ❌ Stub

File Structure

include/
├── MCP_Tool_Handler.h          # Base class for all tool handlers
├── Config_Tool_Handler.h       # /mcp/config endpoint handler
├── Query_Tool_Handler.h        # /mcp/query endpoint handler
├── Admin_Tool_Handler.h        # /mcp/admin endpoint handler
├── Cache_Tool_Handler.h        # /mcp/cache endpoint handler
├── Observe_Tool_Handler.h      # /mcp/observe endpoint handler
├── MySQL_Tool_Handler.h        # Legacy (wrapped by Query_Tool_Handler)
├── MCP_Thread.h                # MCP_Threads_Handler (manages all handlers)
├── MCP_Endpoint.h              # MCP_JSONRPC_Resource (HTTP endpoint)
└── ProxySQL_MCP_Server.hpp     # HTTPS server

lib/
├── Config_Tool_Handler.cpp
├── Query_Tool_Handler.cpp
├── Admin_Tool_Handler.cpp
├── Cache_Tool_Handler.cpp
├── Observe_Tool_Handler.cpp
├── MySQL_Tool_Handler.cpp
├── MCP_Thread.cpp
├── MCP_Endpoint.cpp
└── ProxySQL_MCP_Server.cpp

doc/MCP/
├── Architecture.md             # Detailed architecture documentation
├── VARIABLES.md                # Configuration variables reference
└── README.md                   # Module overview

TODO List

Phase 1: Complete Core Implementation ✅

  • Create MCP_Tool_Handler base class interface
  • Create Config_Tool_Handler (functional)
  • Create Query_Tool_Handler (wraps MySQL_Tool_Handler)
  • Create Admin_Tool_Handler (stub)
  • Create Cache_Tool_Handler (stub)
  • Create Observe_Tool_Handler (stub)
  • Update MCP_Threads_Handler to manage all 5 handlers
  • Update ProxySQL_MCP_Server to pass correct handler to each endpoint
  • Update MCP_JSONRPC_Resource to use tool handler base class
  • Update lib/Makefile to include new source files
  • Create Architecture.md documentation
  • Verify compilation succeeds

Phase 2: Implement Per-Endpoint Authentication

  • Implement authenticate_request() in MCP_Endpoint.cpp
  • Use mcp-{endpoint}_endpoint_auth variables for validation
  • Support Bearer token from Authorization header
  • Return proper 401 Unauthorized on auth failure
  • Document authentication in Architecture.md

Phase 3: Implement Admin Tool Handler

  • admin_list_users - Query mysql_users table
  • admin_show_processes - Query stats_mysql_connection_pool or similar
  • admin_kill_query - Implement KILL QUERY functionality
  • admin_flush_cache - Implement cache flush commands
  • admin_reload - Implement LOAD USERS/SERVERS TO RUNTIME
  • Add proper error handling and validation

Phase 4: Implement Cache Tool Handler

  • get_cache_stats - Query cache statistics from stats_mysql_query_cache
  • invalidate_cache - Implement cache invalidation
  • set_cache_ttl - Configure cache TTL settings
  • clear_cache - Clear all cache entries
  • warm_cache - Execute queries to warm up cache
  • get_cache_entries - List cached queries
  • Add proper error handling and validation

Phase 5: Implement Observe Tool Handler

  • list_stats - List all available ProxySQL statistics
  • get_stats - Get specific statistic values
  • show_connections - Query connection pool statistics
  • show_queries - Query query statistics from stats_mysql_queries_digest
  • get_health - Aggregate health check (backend status, etc.)
  • show_metrics - Query Prometheus metrics
  • Add proper error handling and validation

Phase 6: Complete Config Tool Handler

  • reload_config - Implement proper Admin_FlushVariables integration
    • Support "disk" → LOAD MYSQL VARIABLES FROM DISK
    • Support "memory" → Not applicable
    • Support "runtime" → LOAD MYSQL VARIABLES TO RUNTIME
  • Add proper error handling and validation
  • Test with running ProxySQL instance

Phase 7: Testing & Validation

  • Integration test each endpoint with curl/gh
  • Test tool discovery via tools/list
  • Test tool execution via tools/call
  • Test authentication (when implemented)
  • Test error handling for invalid requests
  • Update test_mcp_tools.sh to use dynamic tool discovery
  • Add integration tests for new endpoints

Phase 8: Documentation

  • Update doc/MCP/Architecture.md with implementation details
  • Add examples for each endpoint in Architecture.md
  • Create end-user guide for using MCP endpoints
  • Document tool schemas in detail
  • Add troubleshooting section

Phase 9: Optional Enhancements

  • Per-endpoint MySQL credentials (different users for different endpoints)
  • Rate limiting per endpoint
  • Request/response logging per endpoint
  • Metrics for tool usage (which tools are called most)
  • WebSocket support for real-time observability
  • Add more tools to Query_Tool_Handler (e.g., describe_view)

Testing Commands

# Test each endpoint's tools
curl -k -X POST https://127.0.0.1:6071/mcp/config \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","method":"tools/list","id":1}'

curl -k -X POST https://127.0.0.1:6071/mcp/query \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","method":"tools/list","id":1}'

# Call a tool
curl -k -X POST https://127.0.0.1:6071/mcp/config \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","method":"tools/call","params":{"name":"get_status","arguments":{}},"id":1}'

Related Files

  • Implementation: include/MCP_*.h, lib/MCP_*.cpp
  • Documentation: doc/MCP/Architecture.md
  • Variables: doc/MCP/VARIABLES.md
  • Test Script: scripts/mcp/test_mcp_tools.sh
  • Configuration Script: scripts/mcp/configure_mcp.sh

Reference

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