Quoting the official announcement:
“Today we released support for the new .NET Core 2.1.0 runtime in AWS Lambda. You can now take advantage of this version’s more performant HTTP client. This is particularly important when integrating with other AWS services from your AWS Lambda function. You can also start using highly anticipated new language features such as Span<T> and Memory<T>.
“We encourage you to update your .NET Core 2.0 AWS Lambda functions to use .NET Core 2.1 as soon as possible. Microsoft is expected to provide long-term support (LTS) for .NET Core 2.1 starting later this summer, and will continue that support for three years. Microsoft will end its support for .NET Core 2.0 at the beginning of October, 2018. At that time, .NET Core 2.0 AWS Lambda functions will be subject to deprecation per the AWS Lambda Runtime Support Policy. After three months, you will no longer be able to create AWS Lambda functions using .NET Core 2.0, although you will be able to update existing functions. After six months, update functionality will also be disabled.
The choice here seems obvious: upgrade and get faster HttpClient, new language features, and long-term support; or lose support for your functions targeting .NET Core 2.0 (whatever that actually means).
In order to migrate to .NET Core 2.1, you’ll need the latest tooling – either version 220.127.116.11 of the AWS Toolkit for Visual Studio, or version 2.2.0 of the Amazon.Lambda.Tools NuGet package.
Check out the official announcement at the AWS blog for more information, including additional tips on upgrading.