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Part 6 of 7 · Housekeeping dispatcher series ~5 min read

What the housekeeping dispatcher costs

There is no model in this system and nothing is emailed: the output is a list on a phone. Six thousand room-days a month is a two-hundred-room hotel. Here is where each cent goes.

Key takeaways

  • About $10 a month at 6,000 room-days. Roughly $37 at 24,000 room-days.
  • One Bedrock read per room-day is the only line that scales. Everything else is rounding.
  • Nothing is always-on, so a quiet month genuinely costs almost nothing.
  • State changes and the morning allocation are the whole workload, and both are trivial at hotel scale.
  • The duplicate test runs before the read, so resends are free.
  • The three real risks: a retry loop, storage nobody expires, and a bigger model than the job needs.

The bill at three volumes

These are US East prices at the time of writing, at three volumes that bracket most small businesses. Find the bar closest to your own and read across.

Monthly cost of the housekeeping dispatcher at three volumesA stacked bar chart with three bars, one per volume tier: 1,500 room-days totalling about $4, 6,000 room-days totalling about $10, and 24,000 room-days totalling about $37. Each bar is stacked from bands. The largest and fastest-growing is Bedrock, one read per room-day, in teal. Then SES for the messages, in pink. Then S3 and DynamoDB storage in green. Then a fixed orange band for Secrets Manager and AWS Budgets, which is eighty-six cents at every volume. Then a grey band for Lambda, SQS and CloudWatch. A note says the read is the only bar that grows with the business and the orange band never moves.$0$20$40$60$80~$3.511,500 room-days~$10.36,000 room-days~$37.4824,000 room-daysBedrock — one read per room-daySES — asks, results, receiptsS3 + DynamoDBFixed — Secrets Manager, BudgetsLambda, SQS, CloudWatchThe read is the only bar that grows with the business. The orange fixed band never moves.
Fig 1. The monthly bill at three volumes. The teal band — one model read per room-day — is the only part that grows; the orange fixed band is the same 86 cents at every volume.

Line by line

LineAt 6,000 room-daysHow it scales
Bedrock read$0.00Linear. One call per room-day, roughly 1,800 in and 200 out tokens.
SES$3.00Linear. About 0 messages per room-day.
DynamoDB + S3$1.24Storage grows with what you retain, not with throughput.
Lambda + SQS$0.12Linear, and effectively free at this scale.
CloudWatch$0.16Flat, if you set retention. Unbounded if you do not.
Secrets Manager$0.40Flat. One secret, $0.40 a month.
AWS Budgets$0.46Flat. Two actions, so you find out before the bill does.

There is no read line and no messaging line. Compute for the morning allocation and writes for state changes are the entire variable cost.

The three ways this bill surprises you

Every one of these has happened to somebody, and all three are cheap to prevent.

  • Polling for room status from the device. Push the allocation once and let state changes flow the other way; a phone polling every ten seconds across a team is the only way to make this expensive.
  • Storing every state transition forever. The timing data is valuable for a year and not after. Roll up to per-room medians and expire the transitions.
  • Reallocating continuously through the day. Allocate in the morning and adjust by exception; a list that changes under somebody is not usable.

What it costs when nothing happens

This matters more than the headline number for a seasonal business. In a month with nothing to process the bill is the fixed band: Secrets Manager at forty cents, AWS Budgets at forty-six, and a few cents of storage. Call it a dollar. There is no instance to stop and nothing to remember to turn off.

The monthly bill at four volumes plus one failure modeA horizontal row of five boxes. Quiet month, about one dollar. 1,500 room-days, about $4. 6,000 room-days, about $10. 24,000 room-days, about $37. And one bad retry loop, about two hundred dollars. A note says four of these are the design working and the fifth is a missing dead-letter queue.THE BILL, AT A GLANCEQuiet month~$11,500 room-days~$46,000 room-days~$1024,000 room-days~$37One bad loop~$200Four of these are the design working. The fifth is a missing dead-letter queue.
Fig 2. The bill at a glance, including the one that is not a volume at all. A retry loop with no dead-letter queue costs more than every legitimate use of the system put together.
  • Management
  • Analytics
  • Front-end & mobile

Set these on day one

  • A dead-letter queue on every SQS queue, with a maximum receive count of three.
  • Thirty-day retention on every CloudWatch log group. There is no default that is safe.
  • An S3 lifecycle rule on the object prefix, tiering at 90 days and expiring at your actual record-keeping horizon.
  • Two AWS Budgets actions — one that emails at half your expected spend, one at double it. The second is how you find out about a loop in an hour instead of a month.
  • Provisioned concurrency: none. Nothing here is latency-sensitive enough to justify paying for a warm function.

Next: the same system drawn for engineers — service names, resource identifiers, IAM scopes, table schemas and the model id.

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