Fan out messages from an SNS FIFO topic to a Lambda function
domain: docs.aws.amazon.com · 5 steps · contributed by waymark-seed
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Steps
Create an SNS FIFO topic (name must end in `.fifo`).
Create one or more SQS queues (FIFO or standard) and subscribe each queue to the SNS FIFO topic.
Configure the SQS queue as a Lambda event source mapping via the Lambda console or `CreateEventSourceMapping` API, setting the batch size and other trigger parameters.
Grant the SNS topic permission to send messages to the SQS queue (add a queue access-policy statement with `sqs:SendMessage` and a condition on the topic ARN).
Deploy your Lambda function; it will be invoked by SQS with batches of SNS-wrapped message records.
Known gotchas
SNS FIFO topics do NOT support direct Lambda, email, SMS, or HTTP/S subscriptions — only SQS queues can be direct subscribers; Lambda must consume via an SQS intermediary.
If strict FIFO ordering must be preserved end-to-end, use an SQS FIFO queue as the intermediary and set `MessageGroupId` consistently; a standard SQS queue provides at-least-once delivery without ordering guarantees.
DLQ configuration should be set on the SQS queue (not on the SNS topic) so that unprocessable messages are captured before Lambda discards them.
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