HAProxy Full config for MCP Streaming HTTP

haproxy.cfg

# /etc/haproxy/haproxy.cfg

global
    log stdout format raw local0

defaults
    mode http
    timeout client 50000
    timeout server 50000
    timeout connect 5000

frontend mcp_frontend
    bind :80
    log global

    # --- Request Validation ---
    # Define ACLs to check for required Accept header values.
    acl accept_events req.hdr(accept) -m sub text/event-stream
    acl accept_json   req.hdr(accept) -m sub application/json

    # Deny GET requests if they don't accept event-stream.
    http-request deny if METH_GET !accept_events

    # Deny POST requests if they don't accept both event-stream and json.
    http-request deny if METH_POST !accept_events or METH_POST !accept_json

    # Send valid requests to the backend servers.
    default_backend mcp_servers

backend mcp_servers
    balance roundrobin

    # --- Session Persistence ---
    # Define a stick table to track sessions.
    # - type: string (for the session ID)
    # - len: 64 (max length of the ID)
    # - size: 1m (can store 1 million entries)
    # - expire: 1h (remove entries after 1 hour of inactivity)
    stick-table type string len 64 size 1m expire 1h

    # For subsequent requests, stick to a server if the client
    # sends the mcp-session-id header we already know.
    stick on hdr(mcp-session-id)

    # For the first response, learn and store the session ID
    # that the server sends back.
    stick store-response res.hdr(mcp-session-id)

    # --- Server Definitions ---
    # Add your MCP servers here.
    server mcp_server_1 10.0.1.10:8000 check
    server mcp_server_2 10.0.1.11:8000 check
    
    # server mcp_server_3 ...