The Node.js Mistake That Cost My Client $3,000 in AWS Bills

Last year I was asked to investigate a startup's AWS bill.

It had jumped from roughly $200/month to over $3,000 in a few weeks.

Nobody knew why.

After digging through logs, metrics, and database traffic, I found the culprit: a polling loop with no backoff strategy.

The code looked harmless:

async function processQueue() {
  const jobs = await getJobs()

  for (const job of jobs) {
    await processFile(job)
  }

  processQueue()
}

processQueue()

At first glance, this seems reasonable. Process all available jobs, then check again.

The problem appears when the queue is empty.

When getJobs() returned no work, the loop immediately queried the database again. And again. And again.

There was no delay, no backoff, and no event-driven trigger.

As a result, the service continuously hammered the database looking for work that didn't exist.

Each iteration generated:

A database query
Network traffic
CPU usage
Logging overhead
Additional infrastructure load

Individually, each operation was cheap.

Executed hundreds of thousands of times per day, they became expensive.

The fix was simple:

async function processQueue() {
  while (true) {
    const jobs = await getJobs()

    for (const job of jobs) {
      await processFile(job)
    }

    await new Promise(resolve => setTimeout(resolve, 5000))
  }
}