Are triggers lost when new lambda instances cannot be spawned?

Question

I would like to trigger an Amazon Lambda Function for every new object uploaded to a bucket in S3. However, I am worried that new instances could fail if more than 100 objects are uploaded at once. This is because lambda has a default concurrency limit of 100 Lambda instances. Meaning that, new instances would not be spawned immediately.

Answer 1

No, events are not lost when lambda hits the Concurrent execution limit.

Amazon S3 invoke lambda asynchronously, asynchronous events are queued first before they are used to invoke the lambda function, and when these events exceed the safety limit (i.e., 100 concurrent executions per region by default) the throttled events are automatically retried for up to six hours, with delays between retries.

Refer Safety Limit in concurrent executions.