Skip to content
allanninal.dev/build
Collaborate

Part 6 of 7 · Allergen checker series ~5 min read

What the allergen checker costs

The only model call is reading a specification document, and those arrive a few times a week rather than daily. Four hundred ingredients is a substantial menu across a few sites. Here is where each cent goes.

Key takeaways

  • About $202 a month at 400 ingredients. Roughly $754 at 1,500 ingredients.
  • One Bedrock read per ingredient is the only line that scales. Everything else is rounding.
  • Nothing is always-on, so a quiet month genuinely costs almost nothing.
  • Specification reading is the only variable, and it falls as suppliers move to structured data.
  • 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 allergen checker at three volumesA stacked bar chart with three bars, one per volume tier: 120 ingredients totalling about $61, 400 ingredients totalling about $202, and 1,500 ingredients totalling about $754. Each bar is stacked from bands. The largest and fastest-growing is Bedrock, one read per ingredient, 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$250$500$750$1000~$61.42120 ingredients~$201.84400 ingredients~$753.521,500 ingredientsBedrock — one read per ingredientSES — 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 ingredient — is the only part that grows; the orange fixed band is the same 86 cents at every volume.

Line by line

LineAt 400 ingredientsHow it scales
Bedrock read$200.00Linear. One call per ingredient, roughly 1,800 in and 200 out tokens.
SES$0.20Linear. About 0.05 messages per ingredient.
DynamoDB + S3$0.34Storage 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.

The read band is specification documents rather than ingredients; it is expressed per ingredient for comparability. Messaging is the daily briefing and change flags.

The three ways this bill surprises you

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

  • Re-reading a specification on every roll-up. The declaration is extracted once per document version and cached against its hash.
  • Recursing the full recipe tree on every lookup. Roll-ups are computed when something changes and stored, not derived at the moment a customer asks.
  • Storing only the latest specification. Not a cost problem: it makes change detection impossible, which is the main thing this system does.

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. 120 ingredients, about $61. 400 ingredients, about $202. 1,500 ingredients, about $754. 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~$1120 ingredients~$61400 ingredients~$2021,500 ingredients~$754One 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.

All posts