Stateful query throttling. Currently only throttles ANY queries.

We should throttle ANY and RRSIG queries to discourage use of our authoritative name servers for reflection/amplification attacks.

Configuration

{erldns, [
    {query_throttle, #{
        enabled := boolean(), %% defaults to true
        limit := non_neg_integer(), %% Number of queries to allow, defaults to 1
        ttl := non_neg_integer(), %% Seconds, defaults to 30
    }}
]}

Telemetry events

[erldns, pipeline, throttle]

Emitted when the query throttle pipe stops the request (e.g. UDP client over limit); response is truncated.

• Measurements: #{count => non_neg_integer()} — request count that triggered throttle
• Metadata: #{transport => udp, host => host()}