mirror of
https://github.com/samjage/metro-warden.git
synced 2026-06-06 01:20:42 +00:00
131 lines
4.1 KiB
Python
131 lines
4.1 KiB
Python
"""
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DNS Plugin — monitors DNS resolution, configured resolvers, and query health.
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Publishes to:
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dns.resolvers — list of configured nameservers
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dns.health — last query round-trip time and result
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dns.query.result — result of a DNS query
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"""
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from __future__ import annotations
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import asyncio
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import logging
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import socket
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import time
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from typing import Any, Dict, List, Optional
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from plugins.base import BasePlugin
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log = logging.getLogger(__name__)
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DEFAULT_POLL_INTERVAL = 30.0
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HEALTH_CHECK_HOST = "one.one.one.one"
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def _read_resolvers() -> List[str]:
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"""Parse /etc/resolv.conf for nameserver entries."""
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resolvers: List[str] = []
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try:
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with open("/etc/resolv.conf") as fh:
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for line in fh:
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line = line.strip()
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if line.startswith("nameserver"):
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parts = line.split()
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if len(parts) >= 2:
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resolvers.append(parts[1])
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except OSError:
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pass
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return resolvers
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def _check_dns_health(host: str) -> Dict:
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"""Perform a synchronous DNS health check and return timing info."""
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start = time.monotonic()
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error: Optional[str] = None
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resolved: Optional[str] = None
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try:
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resolved = socket.gethostbyname(host)
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except socket.gaierror as exc:
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error = str(exc)
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elapsed_ms = (time.monotonic() - start) * 1000.0
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return {
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"host": host,
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"resolved": resolved,
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"elapsed_ms": round(elapsed_ms, 2),
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"error": error,
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"healthy": error is None,
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}
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class DNSPlugin(BasePlugin):
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"""
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Monitors DNS resolver configuration and performs periodic health checks.
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Publishes resolver info and query health to the event bus.
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"""
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name = "dns"
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version = "1.0.0"
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description = "Monitors DNS resolver configuration and query health"
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tags = ["network", "dns"]
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def __init__(
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self,
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bus=None,
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state=None,
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poll_interval: float = DEFAULT_POLL_INTERVAL,
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health_host: str = HEALTH_CHECK_HOST,
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) -> None:
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super().__init__(bus=bus, state=state)
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self._poll_interval = poll_interval
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self._health_host = health_host
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self._task: asyncio.Task | None = None
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self._running = False
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def on_load(self) -> None:
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super().on_load()
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self.subscribe("dns.query") # allow other plugins to request queries
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self._running = True
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try:
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loop = asyncio.get_running_loop()
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self._task = loop.create_task(self._poll_loop())
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except RuntimeError:
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self._log.debug("no running event loop at load time; task deferred")
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def on_unload(self) -> None:
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self._running = False
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if self._task and not self._task.done():
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self._task.cancel()
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super().on_unload()
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async def _poll_loop(self) -> None:
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self._log.debug("dns poll loop started (interval=%.1fs)", self._poll_interval)
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while self._running:
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try:
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resolvers = await asyncio.to_thread(_read_resolvers)
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self.state_set("dns.resolvers", resolvers)
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if self._bus:
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await self._bus.publish("dns.resolvers", {"nameservers": resolvers})
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health = await asyncio.to_thread(_check_dns_health, self._health_host)
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self.state_set("dns.health", health)
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if self._bus:
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await self._bus.publish("dns.health", health)
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except asyncio.CancelledError:
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break
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except Exception as exc:
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self._log.error("dns poll error: %s", exc)
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await asyncio.sleep(self._poll_interval)
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self._log.debug("dns poll loop stopped")
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def on_event(self, topic: str, data: Any) -> None:
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if topic == "dns.query" and isinstance(data, dict):
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host = data.get("host", "")
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if host:
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asyncio.ensure_future(self._resolve_and_publish(host))
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async def _resolve_and_publish(self, host: str) -> None:
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result = await asyncio.to_thread(_check_dns_health, host)
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if self._bus:
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await self._bus.publish("dns.query.result", result)
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