test0r
17af91a99b
Three fixes addressing the recurring "hub wedges on offline backends" class
of failures (2 incidents in 24h, root-caused to single-threaded Lua + an
uninterruptible os.execute ssh call):
1. Hard wall-clock cap on ssh fallback via GNU `timeout --kill-after=2 30`.
ConnectTimeout alone only bounds TCP connect; a half-dead sshd (auth
stall, remote bash-s hang) used to freeze the whole event loop
indefinitely. Configurable via LMCP_HUB_SSH_HARD_TIMEOUT. Also adds
ServerAliveInterval=5/Count=2 so an established-but-dead tunnel dies.
2. Parallel lmcp probes for remote_list_hosts. Shells out a single bash
fan-out of curl -m 3 calls, bounded by PROBE_BUDGET. Wall clock for a
full 12-backend probe went from ~28 s (sum of per-host ssh connect
timeouts) to ~3 s.
3. Probe is lmcp-only — ssh is no longer used as health check. The hub
exists to absorb lots of offline hosts, so an expensive ssh per probe
was the exact wrong tradeoff. Actual remote_* tool calls still fall
through to ssh fallback when lmcp is down.
4. Sticky DOWN cache with exponential backoff: 60 → 120 → 240 → 480 →
900 s. Prevents a sleeping fleet from burning probe budget on every
health check. UP hosts still use 30 s TTL. Tunable via
LMCP_HUB_PROBE_TTL_{UP,DOWN_MIN,DOWN_MAX}.
5. Per-request logging to stderr (tool, host, via, elapsed) — invisible
before, now captured in journal for the next hang's RCA.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
lmcp — Lua MCP server
Lightweight Model Context Protocol (MCP) server in pure Lua.
Runtime dependencies
- Lua 5.1+
- luasocket — needed for the TCP
listener. Packaged as
lua-socketon Arch/ALARM,lua-socketon Debian.
Files
| File | Role |
|---|---|
lmcp.lua |
library: protocol handling, tool registration |
server.lua |
HTTP server loop |
json.lua |
vendored JSON encoder/decoder |
example_server.lua |
sample server with a couple of tools |
Install
Packaged as lmcp in the marfrit overlay repo:
# Arch / ALARM
sudo pacman -S lmcp
# Debian
sudo apt install lmcp
Files land under /usr/share/lua/5.4/ (Lua LUA_PATH).
The example server installs as /usr/bin/lmcp-example.