My First AWS Lambda Using .NET Core

As I prepare for the AWS Certified Solutions Architect – Associate exam, I have a need to play with more services. It’s crucial to gain hands on experience with these AWS services. It’s not enough to just read white-papers and faqs. I’ve heard good thing about AWS Lambda and now it’s time to build something with it. In this post I want to share how I was able to create my first Lambda function using .NET Core.

Before we dive into AWS Lambda, let’s understand what it is. Lambda is a service that allows you to run code without thinking about provisioning or managing servers. You upload your code and AWS handles the rest. Nice! Here is the official summary, “AWS Lambda lets you run code without provisioning or managing servers. With Lambda, you can run code for virtually any type of application or backend service – all with zero administration. Just upload your code and Lambda takes care of everything required to run and scale your code with high availability. You can set up your code to automatically trigger from other AWS services or call it directly from any web or mobile app.”

Now that we know what Lambda is, let’s install the require software to create a Lambda function using .NET Core. First install the lambda templates using nuget. Using a terminal or command prompt, type “dotnet new -i Amazon.Lambda.Templates”. It will install lambda templates so you can get up and running quickly. To test it, type “dotnet new” and press enter. You should see the following templates:

As you can see from the screenshot above, there are 2 categories of templates: lambda functions and lambda serverless. To keep it simple, I’m going to use a simple lambda function that integrates with S3. Now we need to install the AWS Lambda global tool. Using a terminal/command, type “dotnet tool install -g Amazon.Lambda.Tools”.

With the required software installed, it’s time to create our first Lambda using .NET Core. Using a terminal/command, create a new directory called “firstLambda” and cd into it. Now type dotnet new lambda.S3 to create a new function using AWS lambda templates. After creating the function, we need to update a config files with a profile and region. Using a text editor or IDE, open up the new project and update the profile and region setting in aws-lambda-tools-defaults.json.

AWS Lambda will use these settings to deploy and run your function. Let’s take a look at the Function.cs file.

The constructor takes an IAmazonS3 object and the async method FunctionHandler is where our main logic lives. Our lambda function is triggered by a S3 event like a delete object or put object event. Using the same event information, we retrieve the object’s metadata using GetObjectMetadataAsync and finally returning the contentType.

Let’s deploy our first lambda function to AWS using the CLI. Using a terminal/command window, type “dotnet lambda deploy-function agileraymond-1st-lambda”. I’m using agileraymond-1st-lambda as my function name. This command uses the profile and region in our config file so you have to make sure permissions are set correctly. Otherwise you will get errors. Also the command will ask you to provide a role or give you the option to create a new role. If you want to verify that your function made it to AWS, check the AWS lambda console.

To test our new lambda function locally, we can use the test project that was created along with our new function.

Go back to the terminal window and type “dotnet test” to run the integration test. If everything is setup correctly, you will see 1 passing test. That’s it for this post. In a future post, I’m going to test it using the AWS console.