Updating an AWS Lambda app to from .NET Core 2.1 to 3.1

April 2, 2020 - 2 minutes read - 404 words

The long awaited support for .NET Core 3.1 on AWS Lambda has finally been released. My Twitter bot runs on .NET Core 2.1 in a Lambda function and I have been meaning to update it to .NET Core 3.1 since the beginning. So let’s do just that!

I’ll be following the steps on the announcement blog post to migrate to 3.1.

Project file

First up, the TargetFrameowrk in the project file (csproj) needs to be updated, so let’s do that:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>netcoreapp3.1</TargetFramework>
    ...
  </PropertyGroup>
</Project>

CloudFormation template

The runtime also needs to be updated in my CloudFormation template:

...
Resources:
  Retweet:
    ....
    Properties:
      ...
      Runtime: dotnetcore3.1
      ...

CodeBuild script

I’m using AWS CodeBuild for CI, and I should also update the .NET version that is used to build the app:

version: 0.2
phases:
  install:
    runtime-versions:
        dotnet: 3.1
        ...

Note: I had to update my CodeBuild image to aws/codebuild/standard:4.0 as this is the version they added support for 3.1 in. See this comment for more details.

NuGet packages

The last step for my project is to update any NuGet packages to the latest versions. For that, I’ll use the very helpful .NET Tool dotnet-outdated, which can automatically update package versions for you:

$ dotnet-outdated src/DotNetTwitterBot/DotNetTwitterBot.csproj -u
» DotNetTwitterBot
  [.NETCoreApp,Version=v3.1]
  AWSSDK.SecretsManager  3.3.101.72 -> 3.3.102.18

Version color legend:
<red>   : Major version update or pre-release version. Possible breaking changes.
<yellow>: Minor version update. Backwards-compatible features added.
<green> : Patch version update. Backwards-compatible bug fixes.

Upgrading package AWSSDK.SecretsManager...
Project DotNetTwitterBot [.NETCoreApp,Version=v3.1] upgraded successfully

Elapsed: 00:00:26.1976434

New features

There are lots of new features that come with .NET Core 3.1 that can be utilised in AWS Lambda, such as:

New Lambda JSON serializer
ReadyToRun for better cold start performance
Updated AWS Mock .NET Lambda Test Tool

But, I thought to leave these for other blog posts.

Cool! That’s it for my app then. Let’s merge this into master and see how it goes!

Summary

In this post, we updated my Twitter bot app from .NET Core 2.1 to 3.1. This was pretty straight forward, just updating a the version in a few files and updating some NuGet packages. It was a very painless exercise and I recommend everyone do it for their apps; there’s lots of performance improvements in 3.1 so if all of our code runs faster, that hopefully a lot of CO2 we could be saving!