haproxy-mcp/mcp/server.py

#!/usr/bin/env python3
"""HAProxy MCP Server - Direct Runtime API Integration

This module provides an MCP (Model Context Protocol) server for managing HAProxy
configuration and runtime state. It supports dynamic domain/server management
with HTTP backends (SSL termination at HAProxy frontend).
"""

import socket
import subprocess
import re
import json
import logging
import os
import tempfile
import time
import fcntl
from typing import Any, Dict, Generator, List, Optional, Set, Tuple
from mcp.server.fastmcp import FastMCP

# Configure structured logging
logging.basicConfig(
    level=logging.INFO,
    format='%(asctime)s [%(levelname)s] %(message)s',
    datefmt='%Y-%m-%d %H:%M:%S'
)
logger = logging.getLogger(__name__)

mcp = FastMCP("haproxy", host="0.0.0.0", port=8000)

# Constants
HAPROXY_SOCKET: Tuple[str, int] = ("localhost", 9999)
STATE_FILE: str = "/opt/haproxy/data/servers.state"
MAP_FILE: str = "/opt/haproxy/conf/domains.map"
MAP_FILE_CONTAINER: str = "/usr/local/etc/haproxy/domains.map"
SERVERS_FILE: str = "/opt/haproxy/conf/servers.json"
POOL_COUNT: int = 100
MAX_SLOTS: int = 10

# Validation patterns - compiled once for performance
DOMAIN_PATTERN = re.compile(
    r'^[a-zA-Z0-9]([a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])?'
    r'(\.[a-zA-Z0-9]([a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])?)*$'
)
IP_PATTERN = re.compile(r'^(\d{1,3}\.){3}\d{1,3}$')
# Backend/server names: alphanumeric, underscore, hyphen only
BACKEND_NAME_PATTERN = re.compile(r'^[a-zA-Z0-9_-]+$')
# Pattern for converting domain to backend name
NON_ALNUM_PATTERN = re.compile(r'[^a-zA-Z0-9]')

# Limits
MAX_RESPONSE_SIZE = 10 * 1024 * 1024  # 10 MB max response from HAProxy
SUBPROCESS_TIMEOUT = 30  # seconds
STARTUP_RETRY_COUNT = 10  # HAProxy ready check retries
STATE_MIN_COLUMNS = 19  # Minimum columns in HAProxy server state output
SOCKET_TIMEOUT = 5  # seconds for HAProxy socket connection


class HaproxyError(Exception):
    """HAProxy operation error"""
    pass


# CSV field indices for HAProxy stats (show stat command)
class StatField:
    """HAProxy CSV stat field indices."""
    PXNAME = 0      # Proxy name (frontend/backend)
    SVNAME = 1      # Server name (or FRONTEND/BACKEND)
    SCUR = 4        # Current sessions
    SMAX = 6        # Max sessions
    STATUS = 17     # Status (UP/DOWN/MAINT/etc)
    WEIGHT = 18     # Server weight
    CHECK_STATUS = 36  # Check status


# Field indices for HAProxy server state (show servers state command)
class StateField:
    """HAProxy server state field indices."""
    BE_ID = 0       # Backend ID
    BE_NAME = 1     # Backend name
    SRV_ID = 2      # Server ID
    SRV_NAME = 3    # Server name
    SRV_ADDR = 4    # Server address
    SRV_OP_STATE = 5    # Operational state
    SRV_ADMIN_STATE = 6  # Admin state
    SRV_PORT = 18   # Server port


def haproxy_cmd(command: str) -> str:
    """Send command to HAProxy Runtime API.

    Args:
        command: The HAProxy runtime API command to execute

    Returns:
        The response from HAProxy

    Raises:
        HaproxyError: If connection fails or response exceeds size limit
    """
    try:
        with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
            s.settimeout(SOCKET_TIMEOUT)
            s.connect(HAPROXY_SOCKET)
            s.sendall(f"{command}\n".encode())
            s.shutdown(socket.SHUT_WR)
            response = b""
            while True:
                data = s.recv(8192)
                if not data:
                    break
                response += data
                if len(response) > MAX_RESPONSE_SIZE:
                    raise HaproxyError(f"Response exceeded {MAX_RESPONSE_SIZE} bytes limit")
            return response.decode().strip()
    except socket.timeout:
        raise HaproxyError("Connection timeout")
    except ConnectionRefusedError:
        raise HaproxyError("Connection refused - HAProxy not running?")
    except UnicodeDecodeError:
        raise HaproxyError("Invalid UTF-8 in response")
    except HaproxyError:
        raise
    except Exception as e:
        raise HaproxyError(str(e)) from e


def reload_haproxy() -> Tuple[bool, str]:
    """Validate and reload HAProxy configuration.

    Returns:
        Tuple of (success, message)
    """
    try:
        validate = subprocess.run(
            ["podman", "exec", "haproxy", "haproxy", "-c", "-f", "/usr/local/etc/haproxy/haproxy.cfg"],
            capture_output=True, text=True, timeout=SUBPROCESS_TIMEOUT
        )
        if validate.returncode != 0:
            return False, f"Config validation failed:\n{validate.stderr}"

        result = subprocess.run(
            ["podman", "kill", "--signal", "USR2", "haproxy"],
            capture_output=True, text=True, timeout=SUBPROCESS_TIMEOUT
        )
        if result.returncode != 0:
            return False, f"Reload failed: {result.stderr}"
        return True, "OK"
    except subprocess.TimeoutExpired:
        return False, f"Command timed out after {SUBPROCESS_TIMEOUT} seconds"
    except FileNotFoundError:
        return False, "podman command not found"
    except OSError as e:
        return False, f"OS error: {e}"


def validate_domain(domain: str) -> bool:
    """Validate domain format.

    Args:
        domain: The domain name to validate

    Returns:
        True if domain is valid, False otherwise
    """
    if not domain or len(domain) > 253:
        return False
    return bool(DOMAIN_PATTERN.match(domain))


def validate_ip(ip: str, allow_empty: bool = False) -> bool:
    """Validate IPv4 address format.

    Args:
        ip: The IP address to validate
        allow_empty: If True, empty string is considered valid

    Returns:
        True if IP is valid, False otherwise
    """
    if not ip:
        return allow_empty
    if not IP_PATTERN.match(ip):
        return False
    return all(0 <= int(octet) <= 255 for octet in ip.split('.'))


def validate_backend_name(name: str) -> bool:
    """Validate backend or server name to prevent command injection.

    Args:
        name: The backend or server name to validate

    Returns:
        True if name contains only safe characters
    """
    if not name or len(name) > 255:
        return False
    return bool(BACKEND_NAME_PATTERN.match(name))


def domain_to_backend(domain: str) -> str:
    """Convert domain to backend name (alphanumeric + underscore only).

    Args:
        domain: The domain name to convert

    Returns:
        Backend name with non-alphanumeric characters replaced by underscores

    Raises:
        ValueError: If resulting name is invalid
    """
    result = NON_ALNUM_PATTERN.sub('_', domain)
    if not validate_backend_name(result):
        raise ValueError(f"Invalid backend name after conversion: {result}")
    return result


def parse_stat_csv(stat_output: str) -> Generator[Dict[str, str], None, None]:
    """Parse HAProxy stat CSV output into structured data.

    Args:
        stat_output: Raw output from 'show stat' command

    Yields:
        Dictionaries with parsed stat fields for each row
    """
    for line in stat_output.split("\n"):
        if not line or line.startswith("#"):
            continue
        parts = line.split(",")
        if len(parts) > StatField.STATUS:
            yield {
                "pxname": parts[StatField.PXNAME],
                "svname": parts[StatField.SVNAME],
                "scur": parts[StatField.SCUR] if len(parts) > StatField.SCUR else "0",
                "smax": parts[StatField.SMAX] if len(parts) > StatField.SMAX else "0",
                "status": parts[StatField.STATUS],
                "weight": parts[StatField.WEIGHT] if len(parts) > StatField.WEIGHT else "0",
                "check_status": parts[StatField.CHECK_STATUS] if len(parts) > StatField.CHECK_STATUS else "",
            }


def validate_port(port: str) -> bool:
    """Validate port number is in valid range.

    Args:
        port: Port number as string

    Returns:
        True if port is valid (1-65535), False otherwise
    """
    if not port or not port.isdigit():
        return False
    port_num = int(port)
    return 1 <= port_num <= 65535


def get_map_contents() -> List[Tuple[str, str]]:
    """Read domains.map file and return list of (domain, backend) tuples.

    Returns:
        List of (domain, backend) tuples from the map file
    """
    entries = []
    try:
        with open(MAP_FILE, "r", encoding="utf-8") as f:
            try:
                fcntl.flock(f.fileno(), fcntl.LOCK_SH)
            except OSError:
                pass  # Continue without lock if not supported
            try:
                for line in f:
                    line = line.strip()
                    if not line or line.startswith("#"):
                        continue
                    parts = line.split()
                    if len(parts) >= 2:
                        entries.append((parts[0], parts[1]))
            finally:
                try:
                    fcntl.flock(f.fileno(), fcntl.LOCK_UN)
                except OSError:
                    pass
    except FileNotFoundError:
        pass
    return entries


def find_available_pool() -> Optional[str]:
    """Find first unused pool from pool_1 to pool_{POOL_COUNT}.

    Returns:
        Pool name (e.g., 'pool_1') if available, None if all pools are used
    """
    used_pools: Set[str] = set()
    for domain, backend in get_map_contents():
        if backend.startswith("pool_"):
            used_pools.add(backend)

    for i in range(1, POOL_COUNT + 1):
        pool_name = f"pool_{i}"
        if pool_name not in used_pools:
            return pool_name
    return None


def get_domain_backend(domain: str) -> Optional[str]:
    """Look up the backend for a domain from domains.map.

    Args:
        domain: The domain to look up

    Returns:
        Backend name if found, None otherwise
    """
    for map_domain, backend in get_map_contents():
        if map_domain == domain:
            return backend
    return None


def is_legacy_backend(backend: str) -> bool:
    """Check if backend is a legacy static backend (not a pool).

    Args:
        backend: Backend name to check

    Returns:
        True if this is a legacy backend, False if it's a pool
    """
    return not backend.startswith("pool_")


def get_legacy_backend_name(domain: str) -> str:
    """Convert domain to legacy backend name format.

    Args:
        domain: Domain name

    Returns:
        Legacy backend name (e.g., 'api_example_com_backend')
    """
    return f"{domain_to_backend(domain)}_backend"


def save_map_file(entries: List[Tuple[str, str]]) -> None:
    """Save entries to domains.map file atomically.

    Uses temp file + rename for atomic write to prevent race conditions.

    Args:
        entries: List of (domain, backend) tuples to write

    Raises:
        IOError: If the file cannot be written
    """
    dir_path = os.path.dirname(MAP_FILE)
    fd = None
    temp_path = None
    try:
        fd, temp_path = tempfile.mkstemp(dir=dir_path, prefix='.domains.map.')
        with os.fdopen(fd, 'w', encoding='utf-8') as f:
            fd = None  # fd is now owned by the file object
            f.write("# Domain to Backend mapping\n")
            f.write("# Format: domain backend_name\n")
            f.write("# Wildcard: .domain.com matches *.domain.com\n\n")
            for domain, backend in entries:
                f.write(f"{domain} {backend}\n")
        os.rename(temp_path, MAP_FILE)
        temp_path = None  # Rename succeeded, don't unlink
    except OSError as e:
        raise IOError(f"Failed to save map file: {e}") from e
    finally:
        if fd is not None:
            try:
                os.close(fd)
            except OSError:
                pass
        if temp_path is not None:
            try:
                os.unlink(temp_path)
            except OSError:
                pass


def load_servers_config() -> Dict[str, Any]:
    """Load servers configuration from JSON file with file locking.

    Returns:
        Dictionary with server configurations
    """
    try:
        with open(SERVERS_FILE, "r", encoding="utf-8") as f:
            try:
                fcntl.flock(f.fileno(), fcntl.LOCK_SH)
            except OSError:
                logger.debug("File locking not supported for %s", SERVERS_FILE)
            try:
                return json.load(f)
            finally:
                try:
                    fcntl.flock(f.fileno(), fcntl.LOCK_UN)
                except OSError:
                    pass
    except FileNotFoundError:
        return {}
    except json.JSONDecodeError as e:
        logger.warning("Corrupt config file %s: %s", SERVERS_FILE, e)
        return {}


def save_servers_config(config: Dict[str, Any]) -> None:
    """Save servers configuration to JSON file atomically.

    Uses temp file + rename for atomic write to prevent race conditions.

    Args:
        config: Dictionary with server configurations
    """
    dir_path = os.path.dirname(SERVERS_FILE)
    fd = None
    temp_path = None
    try:
        fd, temp_path = tempfile.mkstemp(dir=dir_path, prefix='.servers.json.')
        with os.fdopen(fd, 'w', encoding='utf-8') as f:
            fd = None  # fd is now owned by the file object
            json.dump(config, f, indent=2)
        os.rename(temp_path, SERVERS_FILE)
        temp_path = None  # Rename succeeded, don't unlink
    except OSError as e:
        raise IOError(f"Failed to save servers config: {e}") from e
    finally:
        if fd is not None:
            try:
                os.close(fd)
            except OSError:
                pass
        if temp_path is not None:
            try:
                os.unlink(temp_path)
            except OSError:
                pass


def add_server_to_config(domain: str, slot: int, ip: str, http_port: int) -> None:
    """Add server configuration to persistent storage.

    Args:
        domain: Domain name
        slot: Server slot (1 to MAX_SLOTS)
        ip: Server IP address
        http_port: HTTP port
    """
    config = load_servers_config()
    if domain not in config:
        config[domain] = {}
    config[domain][str(slot)] = {
        "ip": ip,
        "http_port": http_port
    }
    save_servers_config(config)


def remove_server_from_config(domain: str, slot: int) -> None:
    """Remove server configuration from persistent storage.

    Args:
        domain: Domain name
        slot: Server slot to remove
    """
    config = load_servers_config()
    if domain in config and str(slot) in config[domain]:
        del config[domain][str(slot)]
        if not config[domain]:
            del config[domain]
        save_servers_config(config)


def remove_domain_from_config(domain: str) -> None:
    """Remove all server configurations for a domain.

    Args:
        domain: Domain name to remove
    """
    config = load_servers_config()
    if domain in config:
        del config[domain]
        save_servers_config(config)


def get_server_suffixes(http_port: int) -> List[Tuple[str, int]]:
    """Get server suffixes and ports based on port configuration.

    Args:
        http_port: HTTP port for backend

    Returns:
        List of (suffix, port) tuples - always HTTP only
    """
    return [("", http_port)]


def get_backend_and_prefix(domain: str) -> Tuple[str, str]:
    """Look up backend and determine server name prefix for a domain.

    Args:
        domain: The domain name to look up

    Returns:
        Tuple of (backend_name, server_prefix)

    Raises:
        ValueError: If domain cannot be mapped to a valid backend
    """
    backend = get_domain_backend(domain)
    if not backend:
        backend = get_legacy_backend_name(domain)

    if backend.startswith("pool_"):
        server_prefix = backend
    else:
        server_prefix = domain_to_backend(domain)

    return backend, server_prefix


def restore_servers_from_config() -> int:
    """Restore all servers from configuration file.

    Returns:
        Number of servers restored
    """
    config = load_servers_config()
    restored = 0

    for domain, slots in config.items():
        backend = get_domain_backend(domain)
        if not backend:
            continue

        try:
            _, server_prefix = get_backend_and_prefix(domain)
        except ValueError as e:
            logger.warning("Invalid domain '%s': %s", domain, e)
            continue

        for slot_str, server_info in slots.items():
            try:
                slot = int(slot_str)
            except ValueError:
                logger.warning("Invalid slot '%s' for %s, skipping", slot_str, domain)
                continue

            ip = server_info.get("ip", "")
            if not ip:
                continue

            try:
                http_port = int(server_info.get("http_port", 80))
            except (ValueError, TypeError):
                logger.warning("Invalid port for %s slot %d, skipping", domain, slot)
                continue

            try:
                for suffix, port in get_server_suffixes(http_port):
                    server = f"{server_prefix}{suffix}_{slot}"
                    haproxy_cmd(f"set server {backend}/{server} addr {ip} port {port}")
                    haproxy_cmd(f"set server {backend}/{server} state ready")
                restored += 1
            except HaproxyError as e:
                logger.warning("Failed to restore %s slot %d: %s", domain, slot, e)

    return restored


@mcp.tool()
def haproxy_list_domains() -> str:
    """List all configured domains with their backend servers.

    Returns:
        List of domains with their associated backend servers
    """
    try:
        domains = []
        state = haproxy_cmd("show servers state")

        # Build server map from HAProxy state
        server_map: Dict[str, list] = {}
        for line in state.split("\n"):
            parts = line.split()
            if len(parts) >= STATE_MIN_COLUMNS and parts[StateField.SRV_ADDR] != "0.0.0.0":
                backend = parts[StateField.BE_NAME]
                if backend not in server_map:
                    server_map[backend] = []
                server_map[backend].append(
                    f"{parts[StateField.SRV_NAME]}={parts[StateField.SRV_ADDR]}:{parts[StateField.SRV_PORT]}"
                )

        # Read from domains.map (skip wildcard entries starting with .)
        seen_domains: Set[str] = set()
        for domain, backend in get_map_contents():
            if domain.startswith("."):
                continue
            if domain in seen_domains:
                continue
            seen_domains.add(domain)
            servers = server_map.get(backend, ["(none)"])
            backend_type = "pool" if backend.startswith("pool_") else "static"
            domains.append(f"• {domain} -> {backend} ({backend_type}): {', '.join(servers)}")

        return "\n".join(domains) if domains else "No domains configured"
    except HaproxyError as e:
        return f"Error: {e}"


@mcp.tool()
def haproxy_add_domain(domain: str, ip: str = "", http_port: int = 80) -> str:
    """Add a new domain to HAProxy using map-based routing (no reload required).

    Args:
        domain: The domain name to add (e.g., api.example.com)
        ip: Optional IP address for initial server; if provided, adds to slot 1
        http_port: HTTP port for the backend server (default: 80)

    Returns:
        Success message or error description
    """
    # Validate inputs
    if not validate_domain(domain):
        return "Error: Invalid domain format"
    if not validate_ip(ip, allow_empty=True):
        return "Error: Invalid IP address format"
    if not (1 <= http_port <= 65535):
        return "Error: Port must be between 1 and 65535"

    # Check if domain already exists
    existing_backend = get_domain_backend(domain)
    if existing_backend:
        return f"Error: Domain {domain} already exists (mapped to {existing_backend})"

    # Find available pool
    pool = find_available_pool()
    if not pool:
        return f"Error: No available pools (all {POOL_COUNT} pools are in use)"

    try:
        # Update HAProxy map via Runtime API first (immediate effect)
        haproxy_cmd(f"add map {MAP_FILE_CONTAINER} {domain} {pool}")
        haproxy_cmd(f"add map {MAP_FILE_CONTAINER} .{domain} {pool}")

        # Read current map entries and save to file (persistence)
        entries = get_map_contents()
        entries.append((domain, pool))
        entries.append((f".{domain}", pool))
        save_map_file(entries)

        # If IP provided, add server to slot 1
        if ip:
            for suffix, port in get_server_suffixes(http_port):
                server = f"{pool}{suffix}_1"
                haproxy_cmd(f"set server {pool}/{server} addr {ip} port {port}")
                haproxy_cmd(f"set server {pool}/{server} state ready")

            # Save to persistent config
            add_server_to_config(domain, 1, ip, http_port)

            return f"Domain {domain} added to {pool} with server {ip}:{http_port}"

        return f"Domain {domain} added to {pool} (no servers configured)"

    except HaproxyError as e:
        return f"Error: {e}"
    except IOError as e:
        return f"Error: Failed to update map file: {e}"


@mcp.tool()
def haproxy_remove_domain(domain: str) -> str:
    """Remove a domain from HAProxy (no reload required for pool-based domains).

    Args:
        domain: The domain name to remove

    Returns:
        Success message or error description
    """
    if not validate_domain(domain):
        return "Error: Invalid domain format"

    # Look up the domain in the map
    backend = get_domain_backend(domain)
    if not backend:
        return f"Error: Domain {domain} not found"

    # Check if this is a legacy backend (not a pool)
    if is_legacy_backend(backend):
        return f"Error: Cannot remove legacy domain {domain} (uses static backend {backend})"

    try:
        # Clear map entries via Runtime API first (immediate effect)
        haproxy_cmd(f"del map {MAP_FILE_CONTAINER} {domain}")
        haproxy_cmd(f"del map {MAP_FILE_CONTAINER} .{domain}")

        # Remove entries from map file (persistence)
        entries = get_map_contents()
        new_entries = [(d, b) for d, b in entries if d != domain and d != f".{domain}"]
        save_map_file(new_entries)

        # Disable all servers in the pool (reset to 0.0.0.0:0)
        for slot in range(1, MAX_SLOTS + 1):
            server = f"{backend}_{slot}"
            try:
                haproxy_cmd(f"set server {backend}/{server} state maint")
                haproxy_cmd(f"set server {backend}/{server} addr 0.0.0.0 port 0")
            except HaproxyError:
                pass  # Ignore errors for individual servers

        # Remove from persistent config
        remove_domain_from_config(domain)

        return f"Domain {domain} removed from {backend}"

    except HaproxyError as e:
        return f"Error: {e}"
    except IOError as e:
        return f"Error: Failed to update map file: {e}"


@mcp.tool()
def haproxy_list_servers(domain: str) -> str:
    """List all servers for a specific domain.

    Args:
        domain: The domain name to list servers for

    Returns:
        List of servers with their addresses and status
    """
    if not validate_domain(domain):
        return "Error: Invalid domain format"

    try:
        backend, _ = get_backend_and_prefix(domain)
        servers = []
        state = haproxy_cmd("show servers state")

        for line in state.split("\n"):
            parts = line.split()
            if len(parts) >= STATE_MIN_COLUMNS and parts[StateField.BE_NAME] == backend:
                addr = parts[StateField.SRV_ADDR]
                status = "active" if addr != "0.0.0.0" else "disabled"
                servers.append(
                    f"• {parts[StateField.SRV_NAME]}: {addr}:{parts[StateField.SRV_PORT]} ({status})"
                )

        if not servers:
            return f"Backend {backend} not found"

        return f"Servers for {domain} ({backend}):\n" + "\n".join(servers)
    except (HaproxyError, ValueError) as e:
        return f"Error: {e}"


@mcp.tool()
def haproxy_add_server(domain: str, slot: int, ip: str, http_port: int = 80) -> str:
    """Add a server to a domain's backend at specified slot.

    Args:
        domain: The domain name to add the server to
        slot: Server slot number (1 to MAX_SLOTS)
        ip: IP address of the server (required)
        http_port: HTTP port (default: 80)

    Returns:
        Success message or error description
    """
    if not validate_domain(domain):
        return "Error: Invalid domain format"
    if not ip:
        return "Error: IP address is required"
    if not validate_ip(ip):
        return "Error: Invalid IP address format"
    if not (1 <= slot <= MAX_SLOTS):
        return f"Error: Slot must be between 1 and {MAX_SLOTS}"
    if not (1 <= http_port <= 65535):
        return "Error: Port must be between 1 and 65535"

    try:
        backend, server_prefix = get_backend_and_prefix(domain)

        results = []
        for suffix, port in get_server_suffixes(http_port):
            server = f"{server_prefix}{suffix}_{slot}"
            haproxy_cmd(f"set server {backend}/{server} addr {ip} port {port}")
            haproxy_cmd(f"set server {backend}/{server} state ready")
            results.append(f"{server} → {ip}:{port}")

        # Save to persistent config
        add_server_to_config(domain, slot, ip, http_port)

        return f"Added to {domain} ({backend}) slot {slot}:\n" + "\n".join(results)
    except (HaproxyError, ValueError, IOError) as e:
        return f"Error: {e}"


@mcp.tool()
def haproxy_remove_server(domain: str, slot: int) -> str:
    """Remove a server from a domain's backend at specified slot.

    Args:
        domain: The domain name to remove the server from
        slot: Server slot number (1 to MAX_SLOTS) to remove

    Returns:
        Success message or error description
    """
    if not validate_domain(domain):
        return "Error: Invalid domain format"
    if not (1 <= slot <= MAX_SLOTS):
        return f"Error: Slot must be between 1 and {MAX_SLOTS}"

    try:
        backend, server_prefix = get_backend_and_prefix(domain)

        # HTTP only - single server per slot
        server = f"{server_prefix}_{slot}"
        haproxy_cmd(f"set server {backend}/{server} state maint")
        haproxy_cmd(f"set server {backend}/{server} addr 0.0.0.0 port 0")

        # Remove from persistent config
        remove_server_from_config(domain, slot)

        return f"Removed server at slot {slot} from {domain} ({backend})"
    except (HaproxyError, ValueError, IOError) as e:
        return f"Error: {e}"


@mcp.tool()
def haproxy_stats() -> str:
    """Get HAProxy status and statistics.

    Returns:
        Key HAProxy metrics (name, version, uptime, connections, etc.)
    """
    try:
        result = haproxy_cmd("show info")
        stats = {}
        for line in result.split("\n"):
            if ":" in line:
                key, value = line.split(":", 1)
                stats[key.strip()] = value.strip()

        important = ["Name", "Version", "Uptime_sec", "CurrConns", "MaxConn", "Run_queue", "Tasks"]
        output = []
        for key in important:
            if key in stats:
                output.append(f"• {key}: {stats[key]}")

        return "\n".join(output) if output else result
    except HaproxyError as e:
        return f"Error: {e}"


@mcp.tool()
def haproxy_backends() -> str:
    """List all HAProxy backends.

    Returns:
        List of all configured backend names
    """
    try:
        result = haproxy_cmd("show backend")
        backends = [line for line in result.split("\n") if line and not line.startswith("#")]
        return "Backends:\n" + "\n".join(f"• {b}" for b in backends)
    except HaproxyError as e:
        return f"Error: {e}"


@mcp.tool()
def haproxy_list_frontends() -> str:
    """List all HAProxy frontends with their status.

    Returns:
        List of frontends with status and session counts
    """
    try:
        result = haproxy_cmd("show stat")
        frontends = []
        for stat in parse_stat_csv(result):
            if stat["svname"] == "FRONTEND":
                frontends.append(
                    f"• {stat['pxname']}: {stat['status']} (sessions: {stat['scur']})"
                )
        if not frontends:
            return "No frontends found"
        return "Frontends:\n" + "\n".join(frontends)
    except HaproxyError as e:
        return f"Error: {e}"


@mcp.tool()
def haproxy_set_server_state(backend: str, server: str, state: str) -> str:
    """Set server state. States: ready (enable), drain (graceful shutdown), maint (maintenance/disable)

    Args:
        backend: Backend name (alphanumeric, underscore, hyphen only)
        server: Server name within the backend
        state: Target state - ready, drain, or maint

    Returns:
        Success message or error description
    """
    if not validate_backend_name(backend):
        return "Error: Invalid backend name (use alphanumeric, underscore, hyphen only)"
    if not validate_backend_name(server):
        return "Error: Invalid server name (use alphanumeric, underscore, hyphen only)"
    if state not in ["ready", "drain", "maint"]:
        return "Error: state must be 'ready', 'drain', or 'maint'"
    try:
        result = haproxy_cmd(f"set server {backend}/{server} state {state}")
        return result if result else f"Server {backend}/{server} set to {state}"
    except HaproxyError as e:
        return f"Error: {e}"


@mcp.tool()
def haproxy_get_server_health(backend: str = "") -> str:
    """Get health status of all servers or servers in a specific backend.

    Args:
        backend: Optional backend name to filter results

    Returns:
        Server health status or error description
    """
    if backend and not validate_backend_name(backend):
        return "Error: Invalid backend name (use alphanumeric, underscore, hyphen only)"
    try:
        result = haproxy_cmd("show stat")
        servers = []
        for stat in parse_stat_csv(result):
            if stat["svname"] not in ["FRONTEND", "BACKEND", ""]:
                if backend and stat["pxname"] != backend:
                    continue
                servers.append(
                    f"• {stat['pxname']}/{stat['svname']}: {stat['status']} "
                    f"(weight: {stat['weight']}, check: {stat['check_status']})"
                )
        return "\n".join(servers) if servers else "No servers found"
    except HaproxyError as e:
        return f"Error: {e}"


@mcp.tool()
def haproxy_set_server_weight(backend: str, server: str, weight: int) -> str:
    """Set server weight (0-256). Weight 0 disables the server for new connections.

    Args:
        backend: Backend name (alphanumeric, underscore, hyphen only)
        server: Server name within the backend
        weight: Server weight from 0 to 256

    Returns:
        Success message or error description
    """
    if not validate_backend_name(backend):
        return "Error: Invalid backend name (use alphanumeric, underscore, hyphen only)"
    if not validate_backend_name(server):
        return "Error: Invalid server name (use alphanumeric, underscore, hyphen only)"
    if not (0 <= weight <= 256):
        return "Error: weight must be between 0 and 256"
    try:
        result = haproxy_cmd(f"set server {backend}/{server} weight {weight}")
        return result if result else f"Server {backend}/{server} weight set to {weight}"
    except HaproxyError as e:
        return f"Error: {e}"


@mcp.tool()
def haproxy_get_connections(backend: str = "") -> str:
    """Get active connections per server.

    Args:
        backend: Optional backend name to filter results

    Returns:
        Connection statistics or error description
    """
    if backend and not validate_backend_name(backend):
        return "Error: Invalid backend name (use alphanumeric, underscore, hyphen only)"
    try:
        result = haproxy_cmd("show stat")
        connections = []
        for stat in parse_stat_csv(result):
            if backend and stat["pxname"] != backend:
                continue
            if stat["svname"] in ["FRONTEND", "BACKEND"]:
                connections.append(
                    f"• {stat['pxname']} ({stat['svname']}): {stat['scur']} current, {stat['smax']} max"
                )
            elif stat["svname"]:
                connections.append(f"  - {stat['svname']}: {stat['scur']} connections")
        return "\n".join(connections) if connections else "No connection data"
    except HaproxyError as e:
        return f"Error: {e}"


@mcp.tool()
def haproxy_reload() -> str:
    """Reload HAProxy configuration (validates config first).

    Returns:
        Success message or error details if validation/reload failed
    """
    success, msg = reload_haproxy()
    if not success:
        return msg
    return "HAProxy configuration reloaded successfully"


@mcp.tool()
def haproxy_check_config() -> str:
    """Validate HAProxy configuration file syntax.

    Returns:
        Validation result or error details
    """
    try:
        result = subprocess.run(
            ["podman", "exec", "haproxy", "haproxy", "-c", "-f", "/usr/local/etc/haproxy/haproxy.cfg"],
            capture_output=True, text=True, timeout=SUBPROCESS_TIMEOUT
        )
        if result.returncode == 0:
            return "Configuration is valid"
        return f"Configuration errors:\n{result.stderr}"
    except subprocess.TimeoutExpired:
        return f"Error: Command timed out after {SUBPROCESS_TIMEOUT} seconds"
    except FileNotFoundError:
        return "Error: podman command not found"
    except OSError as e:
        return f"Error: OS error: {e}"


@mcp.tool()
def haproxy_save_state() -> str:
    """Save current server state to disk atomically.

    Returns:
        Success message or error description
    """
    try:
        state = haproxy_cmd("show servers state")
        dir_path = os.path.dirname(STATE_FILE)
        fd = None
        temp_path = None
        try:
            fd, temp_path = tempfile.mkstemp(dir=dir_path, prefix='.servers.state.')
            with os.fdopen(fd, 'w', encoding='utf-8') as f:
                fd = None  # fd is now owned by the file object
                f.write(state)
            os.rename(temp_path, STATE_FILE)
            temp_path = None  # Rename succeeded, don't unlink
        except OSError as e:
            raise IOError(f"Failed to save state: {e}") from e
        finally:
            if fd is not None:
                try:
                    os.close(fd)
                except OSError:
                    pass
            if temp_path is not None:
                try:
                    os.unlink(temp_path)
                except OSError:
                    pass
        return "Server state saved"
    except HaproxyError as e:
        return f"Error: {e}"
    except IOError as e:
        return f"Error: {e}"


@mcp.tool()
def haproxy_restore_state() -> str:
    """Restore server state from disk.

    Returns:
        Summary of restored servers or error description
    """
    try:
        with open(STATE_FILE, "r", encoding="utf-8") as f:
            try:
                fcntl.flock(f.fileno(), fcntl.LOCK_SH)
            except OSError:
                pass  # Continue without lock if not supported
            try:
                state = f.read()
            finally:
                try:
                    fcntl.flock(f.fileno(), fcntl.LOCK_UN)
                except OSError:
                    pass

        restored = 0
        skipped = 0
        for line in state.split("\n"):
            parts = line.split()
            if len(parts) >= STATE_MIN_COLUMNS and not line.startswith("#"):
                backend = parts[StateField.BE_NAME]
                server = parts[StateField.SRV_NAME]
                addr = parts[StateField.SRV_ADDR]
                port = parts[StateField.SRV_PORT]

                # Skip disabled servers
                if addr == "0.0.0.0":
                    continue

                # Validate names from state file to prevent injection
                if not validate_backend_name(backend) or not validate_backend_name(server):
                    skipped += 1
                    continue

                # Validate IP and port
                if not validate_ip(addr) or not validate_port(port):
                    skipped += 1
                    continue

                haproxy_cmd(f"set server {backend}/{server} addr {addr} port {port}")
                haproxy_cmd(f"set server {backend}/{server} state ready")
                restored += 1

        result = f"Server state restored ({restored} servers)"
        if skipped:
            result += f", {skipped} entries skipped due to validation"
        return result
    except FileNotFoundError:
        return "Error: No saved state found"
    except HaproxyError as e:
        return f"Error: {e}"


def startup_restore() -> None:
    """Restore servers from config file on startup."""
    # Wait for HAProxy to be ready
    for _ in range(STARTUP_RETRY_COUNT):
        try:
            haproxy_cmd("show info")
            break
        except HaproxyError:
            time.sleep(1)
    else:
        logger.warning("HAProxy not ready, skipping restore")
        return

    try:
        count = restore_servers_from_config()
        if count > 0:
            logger.info("Restored %d servers from config", count)
    except (HaproxyError, OSError, ValueError, json.JSONDecodeError) as e:
        logger.warning("Failed to restore servers: %s", e)


if __name__ == "__main__":
    startup_restore()
    mcp.run(transport="streamable-http")