chnage service discovery
This commit is contained in:
Worph
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"""meta-discovery v1 — UDP multicast service discovery.
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Replaces the two file-based mechanisms that required a shared /meta-core
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volume: ``locks/kv-leader.info`` (locating meta-core at boot) and
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``services/<name>-<host>.json`` (the dashboard nav registry). Both answered the
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same question — where is meta-core, and who else is on this network — so one
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announce packet answers both, and discovery scope becomes the docker network
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rather than the mounted volume.
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The normative spec is docs/project-architecture/service-discovery.md.
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Two details this module must get right, both of which fail silently:
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1. **Per-interface fan-out.** A socket that joins with ``INADDR_ANY`` and sends
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via the default route covers exactly one interface. Containers here are
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routinely attached to two docker networks, so we enumerate interfaces and
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join/send on each using a hand-packed ``ip_mreqn``.
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2. **The pin wins.** When ``META_CORE_URL`` is set, the wire is never consulted
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for core selection — otherwise a container that can see two cores could
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latch onto the wrong one.
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"""
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from __future__ import annotations
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import json
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import os
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import socket
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import struct
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import threading
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import time
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from typing import Callable, Dict, List, Optional
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PROTOCOL_VERSION = 1
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DEFAULT_GROUP = "239.255.77.1"
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DEFAULT_PORT = 9399
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DEFAULT_INTERVAL = 10.0
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# A neighbour unseen for interval * this is dropped. Replaces the reaper.
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LIVENESS_FACTOR = 3
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READ_BUFFER = 8192
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TYPE_DISCOVERY = "discovery"
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TYPE_ANNOUNCE = "announce"
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ROLE_CORE = "core"
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ROLE_SERVICE = "service"
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def _env_flag(name: str, default: bool = True) -> bool:
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raw = os.environ.get(name)
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if raw is None or raw == "":
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return default
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return raw.strip().lower() not in ("false", "0", "no", "off")
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def _interface_indexes() -> List[tuple]:
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"""(name, index, ipv4) for every up, non-loopback interface.
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Falls back to a single unspecified entry when the platform cannot
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enumerate, so discovery still works on the default route.
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"""
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out: List[tuple] = []
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try:
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for idx, name in socket.if_nameindex():
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if name == "lo":
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continue
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try:
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# Cheap way to get the interface's IPv4 without netifaces.
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addr = _ipv4_of(name)
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except OSError:
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continue
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if addr:
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out.append((name, idx, addr))
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except (AttributeError, OSError):
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pass
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return out
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def _ipv4_of(ifname: str) -> Optional[str]:
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"""SIOCGIFADDR — avoids a netifaces dependency."""
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import fcntl
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s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
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try:
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packed = struct.pack("256s", ifname[:15].encode("utf-8"))
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return socket.inet_ntoa(fcntl.ioctl(s.fileno(), 0x8915, packed)[20:24])
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except OSError:
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return None
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finally:
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s.close()
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def local_ipv4() -> str:
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"""First non-loopback IPv4, else the hostname. Matches the Go helper."""
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ifaces = _interface_indexes()
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if ifaces:
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return ifaces[0][2]
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return socket.gethostname()
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class MeshNode:
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"""Announces this service, answers probes, tracks neighbours."""
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def __init__(
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self,
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name: str,
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role: str = ROLE_SERVICE,
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instance: Optional[str] = None,
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version: str = "",
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group: str = DEFAULT_GROUP,
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port: int = DEFAULT_PORT,
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interval: float = DEFAULT_INTERVAL,
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enabled: bool = True,
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payload: Optional[Callable[[], dict]] = None,
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) -> None:
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self.name = name
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self.role = role
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self.instance = instance or socket.gethostname()
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self.version = version
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self.group = group
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self.port = port
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self.interval = interval
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self.enabled = enabled
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self._payload = payload
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self._sock: Optional[socket.socket] = None
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self._ifaces: List[tuple] = []
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self._neighbors: Dict[str, dict] = {}
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self._lock = threading.Lock()
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self._send_lock = threading.Lock()
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self._running = False
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self._threads: List[threading.Thread] = []
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self._listeners: List[Callable[[dict], None]] = []
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# -- lifecycle ---------------------------------------------------------
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def start(self) -> None:
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if self._running or not self.enabled:
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if not self.enabled:
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print("[meshdisco] Disabled by configuration")
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return
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sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
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sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
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try:
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sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT, 1)
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except (AttributeError, OSError):
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pass
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sock.bind(("0.0.0.0", self.port))
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# TTL 1: link-local only, never routed.
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sock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, 1)
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self._ifaces = _interface_indexes()
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group_bin = socket.inet_aton(self.group)
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joined = 0
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for ifname, idx, addr in self._ifaces:
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try:
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# ip_mreqn: multiaddr, address (INADDR_ANY), ifindex. The
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# ifindex is what makes this a per-interface join instead of
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# "whatever the routing table picks".
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mreq = group_bin + socket.inet_aton("0.0.0.0") + struct.pack("@i", idx)
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sock.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, mreq)
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joined += 1
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except OSError as e:
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print(f"[meshdisco] Warning: join {self.group} on {ifname} failed: {e}")
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self._sock = sock
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self._running = True
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print(
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f"[meshdisco] Listening on {self.group}:{self.port} as "
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f"{self.name}/{self.instance} (joined {joined} of {len(self._ifaces)} interfaces)"
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)
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for target in (self._read_loop, self._announce_loop):
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t = threading.Thread(target=target, daemon=True)
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t.start()
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self._threads.append(t)
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def stop(self) -> None:
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if not self._running:
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return
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self._running = False
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# Final announce so neighbours drop us immediately rather than waiting
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# out the staleness window.
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try:
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self._send(self._build_announce("stopping"))
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except OSError:
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pass
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if self._sock:
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try:
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self._sock.close()
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except OSError:
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pass
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self._sock = None
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# -- api ---------------------------------------------------------------
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def probe(self) -> None:
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"""Multicast a probe; every listener replies immediately."""
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self._send({"v": PROTOCOL_VERSION, "type": TYPE_DISCOVERY})
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def neighbors(self) -> List[dict]:
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cutoff = time.time() - self.interval * LIVENESS_FACTOR
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with self._lock:
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for key in [k for k, v in self._neighbors.items() if v["lastSeen"] < cutoff]:
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del self._neighbors[key]
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out = list(self._neighbors.values())
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return sorted(out, key=lambda n: n.get("name") or "")
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def neighbors_by_name(self) -> List[dict]:
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best: Dict[str, dict] = {}
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for nb in self.neighbors():
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cur = best.get(nb.get("name") or "")
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if cur is None or nb["lastSeen"] > cur["lastSeen"]:
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best[nb.get("name") or ""] = nb
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return sorted(best.values(), key=lambda n: n.get("name") or "")
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def cores(self) -> List[dict]:
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return [n for n in self.neighbors() if n.get("role") == ROLE_CORE and n.get("urls")]
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def self_announce(self) -> dict:
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msg = self._build_announce("running")
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msg["addr"] = ""
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msg["lastSeen"] = time.time()
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return msg
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def on_announce(self, cb: Callable[[dict], None]) -> None:
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self._listeners.append(cb)
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# -- internals ---------------------------------------------------------
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def _build_announce(self, status: str) -> dict:
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msg = {
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"v": PROTOCOL_VERSION,
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"type": TYPE_ANNOUNCE,
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"name": self.name,
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"instance": self.instance,
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"role": self.role,
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"version": self.version,
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"status": status,
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}
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if self._payload:
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try:
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p = self._payload() or {}
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except Exception:
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p = {}
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if p.get("baseUrl"):
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msg["baseUrl"] = p["baseUrl"]
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if p.get("status") and status == "running":
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msg["status"] = p["status"]
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# Only a core may carry a URLs block.
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if self.role == ROLE_CORE and p.get("urls"):
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msg["urls"] = p["urls"]
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return msg
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def _send(self, msg: dict, dest: Optional[tuple] = None) -> None:
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sock = self._sock
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if sock is None:
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return
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body = json.dumps(msg).encode("utf-8")
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with self._send_lock:
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if dest is not None:
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try:
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sock.sendto(body, dest)
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except OSError as e:
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print(f"[meshdisco] Reply to {dest} failed: {e}")
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return
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# One write per interface — the default route alone reaches a
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# single network.
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for ifname, idx, addr in self._ifaces:
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try:
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sock.setsockopt(
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socket.IPPROTO_IP,
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socket.IP_MULTICAST_IF,
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socket.inet_aton(addr) + socket.inet_aton("0.0.0.0") + struct.pack("@i", idx),
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)
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sock.sendto(body, (self.group, self.port))
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except OSError as e:
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print(f"[meshdisco] Warning: send on {ifname} failed: {e}")
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def _read_loop(self) -> None:
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while self._running:
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sock = self._sock
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if sock is None:
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return
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try:
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data, addr = sock.recvfrom(READ_BUFFER)
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except OSError:
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if not self._running:
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return
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continue
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try:
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msg = json.loads(data.decode("utf-8"))
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except (ValueError, UnicodeDecodeError):
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continue # foreign traffic on the group
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if msg.get("v") != PROTOCOL_VERSION:
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continue
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# Drop our own multicast echo.
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if msg.get("instance") == self.instance and msg.get("name") == self.name:
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continue
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if msg.get("type") == TYPE_DISCOVERY:
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self._send(self._build_announce("running"), dest=addr)
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continue
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if msg.get("type") != TYPE_ANNOUNCE or not msg.get("name"):
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continue
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key = f"{msg['name']}|{msg.get('instance', '')}"
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if msg.get("status") == "stopping":
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with self._lock:
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self._neighbors.pop(key, None)
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continue
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# Source address comes from the packet, never the payload.
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msg["addr"] = addr[0]
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msg["lastSeen"] = time.time()
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with self._lock:
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self._neighbors[key] = msg
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for cb in list(self._listeners):
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try:
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cb(msg)
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except Exception as e:
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print(f"[meshdisco] Listener raised: {e}")
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def _announce_loop(self) -> None:
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self._send(self._build_announce("running"))
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self.probe()
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while self._running:
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time.sleep(self.interval)
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if not self._running:
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return
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try:
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self._send(self._build_announce("running"))
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except OSError:
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pass
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class MetaCoreLocator:
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"""Locates meta-core over UDP, replacing the kv-leader.info read."""
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def __init__(
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self,
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service_name: str,
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base_url: Optional[str] = None,
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version: str = "",
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meta_core_url: Optional[str] = None,
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enabled: Optional[bool] = None,
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) -> None:
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self._pin = (meta_core_url or "").strip() or None
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self._current: Optional[dict] = None
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self._change_callbacks: List[Callable[[], None]] = []
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self._node = MeshNode(
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name=service_name,
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role=ROLE_SERVICE,
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version=version,
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enabled=_env_flag("ENABLE_UDP_DISCOVERY", True) if enabled is None else enabled,
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payload=lambda: {"baseUrl": base_url or f"http://{local_ipv4()}"},
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)
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self._node.on_announce(self._on_announce)
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def _on_announce(self, nb: dict) -> None:
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if nb.get("role") != ROLE_CORE or not nb.get("urls"):
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return
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if self._pin:
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return # pinned: the wire cannot move us
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prev = self._current
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if prev is None:
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self._current = nb["urls"]
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print(f"[meshdisco] meta-core discovered at {nb['urls']['apiUrl']} ({nb.get('addr')})")
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for cb in list(self._change_callbacks):
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try:
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cb()
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except Exception as e:
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print(f"[meshdisco] Change callback raised: {e}")
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return
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if prev.get("apiUrl") == nb["urls"].get("apiUrl"):
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self._current = nb["urls"]
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return
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# A second, different core. Do not flap — keep the first and say so,
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# because on a PCS box this means a client container can see a core it
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# must not use.
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print(
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f"[meshdisco] Ignoring a second meta-core at {nb['urls']['apiUrl']} "
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f"({nb.get('addr')}); staying with {prev.get('apiUrl')}. "
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f"Set META_CORE_URL to pin this explicitly."
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)
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def start(self) -> None:
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if self._pin:
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print(f"[meshdisco] meta-core pinned to {self._pin}; discovery is advisory")
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self._node.start()
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def stop(self) -> None:
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self._node.stop()
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self._change_callbacks = []
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def get_api_url(self) -> Optional[str]:
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if self._pin:
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return self._pin
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if self._current:
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return self._current.get("apiUrl")
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return None
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def get_urls(self) -> Optional[dict]:
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return self._current
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def wait_for_core(self, timeout: Optional[float] = 30.0) -> Optional[str]:
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"""Block until meta-core is located.
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``timeout=None`` waits forever, which is meta-stremio's default
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(LEADER_WAIT_TIMEOUT=0). Re-probes every 500ms rather than waiting out
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an announce interval.
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"""
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deadline = None if timeout is None else time.time() + timeout
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logged = False
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while deadline is None or time.time() < deadline:
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url = self.get_api_url()
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if url:
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return url
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if not logged:
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print("[meshdisco] Waiting for meta-core...")
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logged = True
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self._node.probe()
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time.sleep(0.5)
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return None
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def on_change(self, cb: Callable[[], None]) -> None:
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self._change_callbacks.append(cb)
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def neighbors(self) -> List[dict]:
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return self._node.neighbors_by_name()
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def self_announce(self) -> dict:
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return self._node.self_announce()
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def probe(self) -> None:
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self._node.probe()
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