title: AWS Lambda Throughput
body: <p>From the AWS Lambda FAQ:</p>
  
  <blockquote>
    <p>Q: Is there a limit to the number of AWS Lambda functions I can execute at once?</p>
    
    <p>No. AWS Lambda is designed to run many instances of your functions in
    parallel. However, AWS Lambda has a default safety throttle of 100
    concurrent executions per account per region. If you wish to submit a
    request to increase the throttle of 100 concurrent executions you can
    visit our Support Center, click “Open a new case”, and file a service
    limit increase request.</p>
    
    <p>Q: What happens if my account exceeds the
    default throttle limit on concurrent executions?</p>
    
    <p>On exceeding the throttle limit, AWS Lambda functions being invoked
    synchronously will return a throttling error (429 error code). <strong>Lambda
    functions being invoked asynchronously can absorb reasonable bursts of
    traffic for approximately 15-30 minutes, after which incoming events
    will be rejected as throttled.</strong> In case the Lambda function is being
    invoked in response to Amazon S3 events, events rejected by AWS Lambda
    may be retained and retried by S3 for 24 hours. Events from Amazon
    Kinesis streams and Amazon DynamoDB streams are retried until the
    Lambda function succeeds or the data expires. Amazon Kinesis and
    Amazon DynamoDB Streams retain data for 24 hours.</p>
  </blockquote>
  
  <p>What constitutes 'reasonable bursts' above? Does anyone have specific numbers?</p>