Lambda function is near the concurrent limit

Why do I see this?

One of your Lambda functions has utilized more than 80% of its allocated concurrent limit in the last 24 hours.

What does this mean?

In AWS Lambda, concurrency is the number of requests that your function is serving at a given time. By default AWS Lambda has a soft limit of 1000 concurrent executions per region which applies to all of your functions in the same region.

From this pool of 1000 concurrent executions, you can set aside a reserved number of executions for any particular function using the concurrency configuration option available in the AWS console.

If your function exceeds the configured function-level concurrency limit, AWS Lambda service will start throttling that function by rejecting any further requests.

This event notifies you when more than 80% of the total allocated concurrent limit for one of your Lambda functions has been utilised in the last 24 hours. This will help you take the necessary actions on time to avoid failtures before it's too late.

How do I fix "Lambda function is near the concurrent limit"?

If you were notified of this event for any of your Lambda functions, you will need to determine if your function requires more concurrency. You can calculate your required concurrency limit by multiplying your function's average runtime duration in seconds by the average number of requests per second.

If your function needs an increase in the concurrency limit, you can adjust the function-level concurrency of your function using the concurrency configuration option in the console. In case you are hitting the AWS region limit of 1000 concurrent executions, you can request a concurrency limit increase by opening a quota increase case in Service Quota dashboard in AWS console.