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AwsClientFactories

README.md

AWS Client Factories Example

This example illustrates the use of both the IServiceCollection.UseAwsServices helper and IAwsFactory features. It also takes advantage of IDisposable to dispose the AWS client used in the invocation once it is complete.

Files

Steps to Recreate

  1. Create a new netcoreapp3.1 and add the following packages:

    • Lambdajection
    • AWSSDK.Service (replace service with the aws service you want to use)
    • AWSSDK.SecurityToken
    • Amazon.Lambda.Serialization.SystemTextJson (optional - may use other serializer)

  2. Add a Startup Class and configure services that will be injected into your Lambda Handler in here.

    • For each AWS service, add a line like this: 
      services.UseAwsService<TAmazonService>(); // Replace TAmazonService with the interface type of the client you want to add

  3. Add a Lambda Handler containing the code that will run when the Lambda is invoked.

    • In the constructor, add a parameter like this:
    Handler(IAwsFactory<TAmazonService> serviceFactory) // Replace TAmazonService with the interface type of the client you want to add
    • When you need to assume a role, do the following:
    var client = await serviceFactory.Create("arn:aws:iam::account:role/RoleName");

  4. Create a CloudFormation template for your Lambda.

    • Create a lambda execution role (the serverless transform creates one for us automatically)
    • Create another role that the execution role can assume
    • Give the role that the lambda assumes permissions to do something the execution role cannot
    • Note that we are using the serverless transform in the example, however using the transform is optional.

How it Works

  1. During a build, the Code Generator scans your startup class for instances of serviceCollection.UseAwsService<>().
  2. For each invocation, it figures out the implementation type and adds it to the IoC container, by putting the following in the ConfigureAwsServices method of the LambdaConfigurator subclass: 
    services.AddSingleton<TInterface, TImplementation>();
services.AddSingleton<IAwsFactory<TInterface>, AwsFactory>();
    • A basic IAwsFactory implementation is generated for each service and is added as a subclass to the configurator. If AWSSDK.SecurityToken is not a dependency of your project, the factory is not generated.
  3. When building the Lambda Host / IoC container, the LambdaConfigurator.ConfigureAwsServices method is called, adding the appropriate Amazon Service Clients and factories.