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Once the message has been processed, it should be deleted to keep your queue clean.

While rare, it is possible for a message to show up twice because of AWS SQS at-least-once delivery. Be sure to design your applications to be idempotent (the software should not be adversely affected when processing the same message more than once).    

Resources

• AWS Documentation using the Console
  https://docs.aws.amazon.com/sns/latest/dg/sns-send-message-to-sqs-cross-account.html
• AWS has great documentation and code examples in many different languages.
  https://github.com/awsdocs/aws-doc-sdk-examples
• UMM-Sub schema can be found: 
  https://git.earthdata.nasa.gov/projects/EMFD/repos/unified-metadata-model/browse/subscription/v1.1.1/umm-sub-json-schema.json
  https://cdn.earthdata.nasa.gov/umm/subscription/v1.1.1/umm-sub-json-schema.json
• CMR API documention: 
  https://cmr.earthdata.nasa.gov/ingest/site/docs/ingest/api.html#subscription

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