Before we move on to use cases for AWS Lambda, let's quickly touch on some default resource limits. For each AWS account, there are specific limits for the service and runtime:

• For concurrency, there is a soft limit of 1,000 executions at a time. This can be raised by submitting a service limit increase request in the support center console.
• The size of environment variables can't be greater than 4 KB. You can have an unlimited number of envars, but the whole set cannot exceed 4 KB.
• The size of the invocation payload can be no greater than 6 MB for synchronous requests and 256 KB for asynchronous requests (invocations types will be explained later in this section). This means that, when you invoke a Lambda function, there is a limit to the amount of data you can include with the request. 

Now that we've covered the fundamentals, let's apply this to some use cases to get an idea of how we can use Lambda.