Backpressure — Why a Broker Absorbs Spikes

Push traffic past capacity with no broker and watch the waiting room overflow and drop requests. Add a broker and the same spike is buffered safely — nothing lost — then add a consumer to drain it.

The one idea: putting a broker between producers and consumers lets the system absorb a burst instead of dropping it. That's the how (communication) axis — independent of where the code runs → see Topology vs Communication.

📈 Incoming questions6 req/s

quiet⚠ over capacity (2/s)viral

Incoming

6/s

Handled

0/s

Dropped / timed out

drops past 8 waiting

💬

Producers

6/s

⏳ Waiting roomholds 8

empty — keeping up

Requests wait in memory for the consumer.

Consumers

2 req/s total

Push the rate past capacity and watch the waiting room fill, then start dropping requests — there is no buffer to catch the spike.

Direct or broker? — classify each call

A broker is powerful, but it isn't free — it adds a hop and eventual consistency. For each operation in the contract-risk agent, decide whether it should stay a direct call (the user is waiting) or go through the broker (background, fan-out or long-running).

Answer the manager's question (retrieve → analyze → respond)

Look up the vendor in ERP for this request

Re-score 40 contracts overnight

Route this contract for legal + finance approval

Write the audit-trail entry

Notify the reviewer

What just happened

▹A consumer can only finish so much work per second. When questions arrive faster than that, the extra has to go somewhere.
▹No broker (synchronous): the extra piles up in a tiny waiting room — and once it's full, new requests are simply dropped or time out.
▹With a broker (event-driven): the same spike is buffered safely, so nothing is lost. The backlog drains once traffic calms — and if you need more speed, you add another consumer.
▹But don't broker everything. The live reasoning loop the user is waiting on stays direct; brokers are for the background path — long jobs, fan-out, audit, notifications — where decoupling, buffering or replay actually helps.