Periodic UDP heartbeat sender.

Opens a UDP socket and periodically transmits a phi_accrual_udp heartbeat packet to each configured target. Fire-and-forget — UDP delivery failure is the receiver's problem to detect (which is exactly what phi_accrual is for).

Targets

Each target is a {host, port} tuple. Host can be an IP tuple, a charlist, or an atom; port is an integer. Resolution happens on every send so DNS changes are picked up without restart, at the cost of a lookup per tick.

Sender.start_link(
  targets: [
    {{10, 0, 0, 2}, 4370},
    {~c"peer-c.internal", 4370}
  ],
  interval_ms: 1_000
)

Timestamp source

By default the sender stamps packets with :erlang.system_time(:millisecond) (wall clock, NTP-corrected on most systems). Pass :timestamp_fn to override — for example, to use monotonic time if you don't trust the wall clock.

Telemetry

[:phi_accrual_udp, :sender, :started]
  measurements: %{}
  metadata:     %{interval_ms, target_count}

[:phi_accrual_udp, :sender, :tick]
  measurements: %{sent, errors}
  metadata:     %{}