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The 429 responses issued by API Gateway (when lowering the max concurrent requests and exceeding it) do not have the CORS headers, so the ajax request in the browser just throws error without any info that could selectively make it trigger a retry.

Any workaround but for retrying any error in the client app / i.e. any work around to have AWS include the CORS headers in the 429 response? CORS is enabled in API gateway, the OPTIONS method is there and responds the headers, and a lambda responds them itself (proxy integration) - all works well but for the 429.

Questionless
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I had a similar issue that was resolved by this answer. You need to create a custom response for 4** and 5** templates. You can do it manually in the AWS console, like so: enter image description here Remember to redeploy the API after changing this.

If API Gateway returns 429 you're probably hitting the limit for Lambda's lambda concurrency (or at least that was in my case). The CORS headers are not being sent to the client, since API Gateway blocks the request before hitting your Lambda.

Khrone
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