Extends agent to execute HTTP, TCP, and DNS service checks.
Agent Changes:
- Extended protobuf schema with Check, CheckResult, CheckList messages
- Added checks.go with HTTP/TCP/DNS executors (completely stateless)
- Added checks worker pool (50 workers)
- Handles check_jobs WebSocket event from Phoenix
- Reports check_result back to Phoenix
Check Executors:
- HTTP: Full request support with regex, SSL, headers
- TCP: Port connectivity with send/expect patterns
- DNS: Resolution for A, AAAA, CNAME, MX, TXT records
Architecture: Agent is stateless - receives jobs, executes, reports back.
Phoenix handles all scheduling and state tracking.
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
The old code only tried unprivileged UDP ICMP (udp4), which relies on
the ping_group_range sysctl — not CAP_NET_RAW. Docker doesn't set that
sysctl, so pings always timed out and fell through to exec. Now tries
raw ICMP sockets (ip4:icmp) first, which properly uses CAP_NET_RAW.
Also sets cap_net_raw+ep on the agent binary in the Dockerfile.
Previously the agent proceeded to the main loop without confirming
the server accepted the channel join. A rejected join (e.g. invalid
token) left the agent running but silently non-functional. Now waits
for the join reply with a 10s timeout, returns error on rejection.
Reader goroutine starts before join send so the reply can be received.
Writer goroutine starts after join confirmation.
Previously, resetting slice length to 0 left previous protobuf data
(device IDs, OID values, credentials) in the backing array. Now zeros
the full capacity before returning to the pool.
handleMessage returns bool to signal session end instead of calling
osExit directly. Defers (pool stop, writeCh close, writerWg wait)
now run before exit, preventing in-flight result loss and panics
from writes to closed channels.
Fix 1: Limit inbound job payload size to 4MB to prevent OOM from malicious server
Fix 2: Worker pool submit accepts context and returns bool, prevents blocking event loop
Fix 3: Panic recovery in worker pool goroutines prevents permanent worker death
Fix 4: WebSocket handshake timeout (30s) prevents indefinite blocking on slow server
Fix 5: Writer goroutine propagates errors to main loop via writeErrCh
Use sync.Pool to reuse 4KB byte slices for protobuf marshaling via
MarshalAppend instead of allocating fresh buffers per result message.
Reduces GC pressure under high-throughput polling.
Accumulate SNMP results and flush in batches of 50 or every 100ms,
whichever comes first. Reduces per-message overhead when thousands
of devices produce results near-simultaneously. Also flushes
remaining results on disconnect/shutdown.
Build the entire frame (header + mask key + masked payload) in one
buffer and write it with a single syscall instead of two separate
writes. Removes the failOnNthWrite test that tested the old
two-write implementation detail.
Wrap the WebSocket connection in an 8KB bufio.Reader so that small
reads (2-byte frame headers, length extensions) are served from
buffer instead of making individual syscalls.
Raise write channel from 500 to 10000, SNMP/monitoring result
channels from 1000 to 10000, MikroTik/credential channels to 5000.
Prevents silent data loss when polling thousands of devices.
Replace unbounded goroutine spawning with fixed-size worker pools:
100 workers for SNMP, 20 for MikroTik, 50 for ping. Prevents file
descriptor exhaustion and device overload when handling thousands
of concurrent jobs. Pool provides backpressure when saturated.
Use strconv.FormatInt/FormatUint instead of fmt.Sprintf for integer
conversions in snmpValueToString. Use encoding/hex + strings.Builder
instead of fmt.Sprintf loop in formatHex. Use strconv.FormatUint for
WebSocket ref counter. Reduces allocations per OID significantly.
Previously each OID was fetched individually, meaning 1000 OIDs
required 1000 round trips. Now OIDs are batched into groups of 60
(the SNMP max PDU size), reducing round trips by ~50x. Also
pre-sizes the OID value map to avoid repeated rehashing.
Docker tags cannot contain colons. Use a separate tag-safe format
(colons replaced with hyphens) for Docker tags while keeping the
RFC 3339 timestamp as the version baked into the binary.
add libcap and setcap cap_net_raw+p on /bin/ping so ICMP works
without container-level capabilities. add NET_RAW cap_add to
docker-compose.example.yml as fallback.
- Dockerfile: add BuildKit cache mounts for Go module and build caches,
pin both stages to Alpine 3.23
- CI: replace BUILDKIT_INLINE_CACHE with registry-based layer caching
(mode=max) for branch and release builds
- .dockerignore: exclude test files, Rust legacy, nix, and other
non-build artifacts from Docker context
- SNMP: lower MaxRepetitions from default 50 to 10 to prevent Mikrotik
routers from timing out during bulk walks
