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UDP Send (udp-out)

Sends msg.payload as a UDP datagram. Three modes share the same write path; the differences are setsockopt-level — SO_BROADCAST for broadcast and TTL / loopback / outbound interface for multicast.

Inputs Outputs
1 0

Modes

Mode Behaviour
unicast Send to a single host:port.
broadcast Set SO_BROADCAST on the socket; send to a broadcast address (255.255.255.255 or directed).
multicast IPv4 multicast send with configurable TTL, loopback, and outbound interface.

Configuration

Field Default Description
mode unicast unicast, broadcast, or multicast.
host — Destination host. msg.host overrides.
port — Destination port. msg.port overrides.
bindHost — Multicast only: name of the outbound interface (e.g. eth0).
multicastTTL 1 Multicast only. 1 = LAN-local. Range 0–255.
multicastLoopback true Multicast only. Loopback to the sending host.
reuseSocket true Keep one outbound socket across messages.

Incoming message

Field Description
payload Body to send. string, []byte, []int (number array), or any other type (fmt.Sprint-rendered). Empty is allowed (zero-length datagram is legal in UDP).
host Per-message destination override.
port Per-message destination override.

Status

  • Green sent · 137B → host:port after each successful send.
  • Yellow send: … on transient errors (DNS, kernel buffer full).
  • Red on configuration errors.

Notes

  • Broadcast: the node sets SO_BROADCAST on the socket so the kernel allows writes to broadcast addresses. The default unicast socket would silently fail.
  • Multicast TTL: 1 keeps the packet on the local link. Bump it to traverse routed subnets — but coordinate with your network team because most routers drop multicast.
  • reuseSocket=false opens a fresh socket for every send. Rare; useful only when source-port randomisation is required per packet.

Examples

Send a syslog event.

[Inject every 1s] → [Function format syslog] → [udp-out 192.0.2.5:514]

Multicast discovery beacon.

[Inject every 30s] → [Change payload=…] → [udp-out 224.0.0.251:5353  mode=multicast TTL=1]

Broadcast a heartbeat to the local subnet.

[Inject every 5s] → [udp-out 255.255.255.255:9999  mode=broadcast]

See also