How to store and load custom json appsettings and Connection Strings in an AWS Lambda Project?

Question

I am developing an Alexa Skills Kit app in Visual Studio and have created and AWS Lambda Project in .NET Core 2.0. When creating the project, it automatically comes with a file called aws-lambda-tools-defaults.json. The settings here are used by the AWS Lambda function.

Now, I want to store my own appsettings and Connection Strings for use by the application. What is the preferred route on how I can store my settings and get them in code?

I've gotten as far as adding the NuGet package called Microsoft.Extensions.Configuration.Json. But I'm not sure what I do from here.

1) Do I need to create another json file, or can I use the existing file aws-lambda-tools-defaults.json? If I do need to create a new file, what should it be called?

2) Is there a Constructor I need to add to the Function.cs file in order to load json file?

3) What code can I write that will actually get my settings and Connection Strings?

I'm a bit lost here, so really any advice would be helpful! Thank you!

Answer 1

1. Yes, you do need to create another files, which will be used depending on the environment. However, aws-lambda-tools-defaults.json is not the file that needs to hold the connection strings, and other app configuration settings. Instead, it is the appsettings.json file.

2 and 3. You can follow microsoft's instructions on how to use the configuration files from here on.

Basically, in the Startup file, you can get the configurations via IConfiguration :

Configuration.GetValue<string>("myConfigValue");

Specifically, for aws serverless application with netcore 2.1, if you want to use appsettings.{environment}.json , you can do the following:

    /// <summary>
    /// The Main function can be used to run the ASP.NET Core application locally using the Kestrel webserver.
    /// </summary>
    public static class LocalEntryPoint
    {
        public static IWebHost BuildWebHost(string[] args) =>
            WebHost.CreateDefaultBuilder(args)
                .ConfigureAppConfiguration((builderContext, config) =>
                {
                    string defaultAppSettingsFile = "appsettings.json";

                    // because of a bug in Visual Studio 2017 version 15.8.2 (newest at this time) with NetCore projects, simply changing the configuration won't work
                    // you have to Close, and then Re-open the project in order for the Conditional Compilation Symbols to be taken in effect
#if Debug
                    string appSettingsFileToAdd = "appsettings.Debug.json";
#elif Beta
                    string appSettingsFileToAdd = "appsettings.Beta.json";
#elif Release
                    string appSettingsFileToAdd = "appsettings.Release.json";
#else
                    string appSettingsFileToAdd = "appsettings.Debug.json";
#endif
                    config
                        .AddJsonFile(
                            defaultAppSettingsFile,
                            optional: false,
                            reloadOnChange: true)
                        .AddJsonFile(
                            appSettingsFileToAdd,
                            optional: true,
                            reloadOnChange: true);
                })
                .UseStartup<Startup>()
                .Build();

        public static void Main(string[] args)
        {
            BuildWebHost(args).Run();
        }
    }

Answer 2

You would need to create your own ServiceCollection and the IConfiguration to it. I've created some attraction called ILambdaHost, that does it in a similar way to IHose. I don't no recommend using IWebHost because you don't need a web host functionality inside a Lambda, it would be a lot of overhead.

Here is how you create the configuration class and add the appsettings.json to it.

using Microsoft.Extensions.Configuration;
using System;
using System.IO;

namespace MyNamespace
{
    public static class LambdaConfigurationBuilder
    {
         public static IConfiguration Build() => new ConfigurationBuilder()
           .SetBasePath(Directory.GetCurrentDirectory())
           .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
           .Build();
    }
}