Merge pull request #2 from keviryan/master

detail ec2 rate limit

Author: mwunderl

doc_source/scaling.md

@@ -36,6 +36,14 @@ For example, if there are five active shards on a stream \(that is, you have fiv
 
 ## Automatic Scaling<a name="scaling-behavior"></a>
 
+AWS Lambda will dynamically scale capacity in response to increased traffic, subject to your account's [Account Level Concurrent Execution Limit](concurrent-executions.md#concurrent-execution-safety-limit)\. To handle any burst in traffic, Lambda will immediately increase your concurrently executing functions by a predetermined amount, dependent on which region it's executed \(see table below\)\.
+
+ If the default **Immediate Concurrency Increase** value, as noted in the table below, is not sufficient to accommodate the traffic surge, Lambda will continue to increase the number of concurrent function executions by 500 per minute until your account safety limit has been reached or the number of concurrently executing functions is sufficient to successfully process the increased load\.
+
+**Note**  
+Because Lambda depends on Amazon EC2 to provide Elastic Network Interfaces for VPC\-enabled Lambda functions, these functions are also subject to Amazon EC2's rate limits as they scale\. If Amazon EC2 rate limits prevent VPC\-enabled functions from adding 500 concurrent invocations per minute, please request a limit increase by following the instructions in [Limits](limits.md). When requesting the limit increase however, please use the **Use Case Description** field to include any throttling responses that you may have recieved from EC2, along with details about any previous limit increase\.  
+Beyond this rate \(i\.e\. for applications taking advantage of the full Immediate concurrency increase\), your application should handle Amazon EC2 throttling \(502 EC2ThrottledException\) through client\-side retry and backoff\. For more details, see [Error Retries and Exponential Backoff in AWS](http://docs.aws.amazon.com/general/latest/gr/api-retries.html)\.
+
 AWS Lambda dynamically scales function execution in response to increased traffic, up to your [concurrency limit](limits.md)\. Under sustained load, your function's concurrency bursts to an initial level between 500 and 3000 concurrent executions that varies per region\. After the initial burst, the function's capacity increases by an additional 500 concurrent executions each minute until either the load is accommodated, or the total concurrency of all functions in the region hits the limit\.
 
 
@@ -57,4 +65,4 @@ AWS Lambda dynamically scales function execution in response to increased traffi
 **Note**  
 If your function is connected to a VPC, the [Amazon VPC network interface limit](https://docs.aws.amazon.com/general/latest/gr/aws_service_limits.html#limits_vpc) can prevent it from scaling\. For more information, see [Configuring a Lambda Function to Access Resources in an Amazon VPC](vpc.md)\.
 
-To limit scaling, you can configure functions with *reserved concurrency*\. For more information, see [Managing Concurrency](concurrent-executions.md)\.
+To limit scaling, you can configure functions with *reserved concurrency*\. For more information, see [Managing Concurrency](concurrent-executions.md)\.