Backpressure when pipeline is saturated

An ingestion pipeline with no backpressure mechanism is a cost bomb waiting for a large import. A bulk upload of 500,000 contacts from a newly purchased list can exhaust database connection pools, max out queue worker memory, and cause cascading failures in unrelated services sharing the same infrastructure. CWE-400 (Uncontrolled Resource Consumption) applies when there is no ceiling on how fast upstream producers can push work into the pipeline. ISO 25010:2011 §4.2.6 (resource utilization) requires that systems manage resource consumption under load. The fix cost is low; the blast radius of omitting it is high.

Configure a concurrency ceiling on queue workers and add a queue-depth check in the producer before enqueuing large batches.

// BullMQ worker — cap concurrent jobs
const worker = new Worker('contact-ingestion', processJob, {
  connection,
  concurrency: 5,  // max 5 jobs in flight simultaneously
})

// Producer — check queue depth before bulk enqueue
const queue = new Queue('contact-ingestion', { connection })

export async function enqueueIfNotSaturated(job: ContactIngestionJob) {
  const waiting = await queue.getWaitingCount()
  if (waiting > 1000) {
    throw new Error(
      `Ingestion queue depth is ${waiting} — pipeline is saturated. Retry after current backlog clears.`
    )
  }
  await queue.add('ingest', job)
}

For synchronous ingestion endpoints (no queue), add a rate limit middleware that returns HTTP 429 when request volume exceeds the database's sustainable write throughput.