# How to trigger a S3 event using Cross-Stack References

**URL:** https://discourse.sst.dev/t/how-to-trigger-a-s3-event-using-cross-stack-references/1134
**Category:** General
**Created:** [July 11, 2019, 5:07pm UTC](https://discourse.sst.dev/t/how-to-trigger-a-s3-event-using-cross-stack-references/1134 "2019-07-11T17:07:16Z")
**Posts on this page:** 2
**Page:** 1

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### Author: ![robo](https://avatars.discourse-cdn.com/v4/letter/r/bb73d2/32.png) [@robo](https://discourse.sst.dev/u/robo)
#### Post date: [July 11, 2019, 5:07pm UTC](https://discourse.sst.dev/t/how-to-trigger-a-s3-event-using-cross-stack-references/1134/1 "2019-07-11T17:07:16Z")

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What is the recommended way to setup the serverless.yml file in the case where you are triggering lambda (function) event from an externally created S3 resource?

If you include the events: tag in the function definition, the system fails as it tries to create a new S3 resource instead of using the existing resource created in the other stack.

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### Author: ![jayair](https://yyz2.discourse-cdn.com/flex032/user_avatar/discourse.sst.dev/jayair/32/9_2.png) [@jayair](https://discourse.sst.dev/u/jayair)
#### Post date: [July 15, 2019, 6:03pm UTC](https://discourse.sst.dev/t/how-to-trigger-a-s3-event-using-cross-stack-references/1134/2 "2019-07-15T18:03:25Z")

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I’m not entirely sure about this but are you not referencing the externally created bucket?