Configure C#.Net project to use dll from Lambda layer

Create and Publish Your Lambda Layer

1. Prepare the Layer Directory: Create a directory structure that Lambda expects. For .NET libraries, Lambda layers expect the structure to be as follows:

layer/
└── bin/
    └── netcoreapp3.1/  (or your target framework version)
        └── ABC.dll

2. Zip the Layer: Compress the layer/ directory into a .zip file.
3. Publish the Layer: Use the AWS CLI to publish the layer:

aws lambda publish-layer-version --layer-name "MyDotNetLayer" --zip-file "fileb://layer.zip" --compatible-runtimes dotnetcore3.1

Replace dotnetcore3.1 with your target runtime if different.

Configure Your C#.NET Lambda Project Now, modify your C#.NET project to avoid including ABC.dll in its build output.

1. Reference the DLL Conditionally: In your .csproj file, reference ABC.dll but set it to not copy to the output directory. Assuming you have the DLL locally for development, your reference might look like this:

<ItemGroup>
  <Reference Include="ABC">
    <HintPath>path\to\ABC.dll</HintPath>
    <Private>false</Private> <!-- This prevents the DLL from being included in the output -->
  </Reference>
</ItemGroup>

Setting <Private>false</Private> ensures the DLL is used during development but not packaged into the deployment.

2. Build Your Project: Build your project as usual. Confirm that ABC.dll is not in the build output directory.

Deploy Your Lambda Function

After configuring the layer and the project:

1. Assign the Layer to Your Lambda Function: When creating or updating your Lambda function, specify the layer that includes ABC.dll. This can be done in the AWS Management Console or using the AWS CLI. For example:

aws lambda update-function-configuration --function-name MyFunction --layers arn:aws:lambda:region:account-id:layer:MyDotNetLayer:version-number

2. Deploy Your Function: Deploy your Lambda function package without ABC.dll. Lambda will use the version of ABC.dll provided in the layer.