A simple AWS Lambda for .NET7 + Dependency Injection

ApplicationSettings.cs

namespace SomeLambdaFunction
{
    public class ApplicationSettings
    {
        private const string ConnectionStringEnvironmentalVariableName = "MY_POSTGRES_CONNECTIONSTRING";

        public ApplicationSettings()
        {
            var isMissingEnvironmentalVariableData = false;

            var connectionString = Environment.GetEnvironmentVariable(ConnectionStringEnvironmentalVariableName);
            if (string.IsNullOrWhiteSpace(connectionString))
            {
                Console.WriteLine($"Missing database connection string via Environment Variables: {ConnectionStringEnvironmentalVariableName}");
                isMissingEnvironmentalVariableData = true;
            }
            else
            {
                PostgressDatabaseConnectionString = connectionString;
            }

            // TODO: Add more "config" entries here

            if (isMissingEnvironmentalVariableData)
            {
                throw new Exception("Failed to create application settings because missing at least 1 environmental setting.");
            }
        }

        public string PostgressDatabaseConnectionString { get; }
    }
}

Function.cs

using Amazon.Lambda.Core;
using Amazon.Lambda.RuntimeSupport;
using Amazon.Lambda.Serialization.SystemTextJson;
using Microsoft.Extensions.DependencyInjection;

// *****
// Start of application initialize. AKA cold-start initialization.
// *****

ApplicationSettings applicationSettings = new();

IServiceCollection serviceCollection = new ServiceCollection();

serviceCollection
    .AddLogging() // For services that require an ILogger<T> via ctor injection.
    .AddSingleton<IDatabase>(implementationInstance =>
    {
        Database database = new(applicationSettings.PostgressDatabaseConnectionString);

        return database;

    });

// TODO: Add your own services here.
serviceColltion
    .AddSingleton<IFoo, Foo>()
    .AddSingleton<IBar, Bar>();

var serviceProvider = serviceCollection.BuildServiceProvider();


// *****
// Function handler - where the main business logic goes.
// *****
var handler = new Func<ILambdaContext, Task<bool>>(async (ILambdaContext context) =>
{
    // NOTE: Can this be injected instead? Like, what happens if the host has to shutdown?
    var cancellationToken = new CancellationToken();

    context.Logger.LogDebug("Starting some function - pew pew!");
    
    // Business logic goes here
    
    return true;
});


await LambdaBootstrapBuilder.Create<Task<int>>(handler, new DefaultLambdaJsonSerializer())
        .Build()
        .RunAsync();
        
        
// What happens if you don't want the Function to return anything?
// Use this instead!
//var handler = async (ILambdaContext context) =>
//{
//}
//
//await LambdaBootstrapBuilder.Create<Task>(handler, new DefaultLambdaJsonSerializer())
//        .Build()
//        .RunAsync();