AWS Developer Blog

AWS Lambda Support in Visual Studio

by Norm Johanson | on | in .NET | | Comments

Today we released version 1.9.0 of the AWS Toolkit for Visual Studio with support for AWS Lambda. AWS Lambda is a new compute service in preview that runs your code in response to events and automatically manages the compute resources for you, making it easy to build applications that respond quickly to new information.

Lambda functions are written in Node.js. To help Visual Studio developers, we have integrated with the Node.js Tools for Visual Studio plugin, which you can download here. Once the Node.js plugin and the latest AWS Toolkit are installed, it is easy to develop and debug locally and then deploy to AWS Lambda when you are ready. Let’s walk through the process of developing and deploying a Lambda function.

Setting up the project

To get started, we need to create a new project. There is a new AWS Lambda project template in the Visual Studio New Project dialog.

The Lambda project wizard has three ways to get started. The first option is to create a simple project that just contains the bare necessities to get started developing and testing. The second option allows you to pull down the source of a function that was already deployed. The last option allows you to create a project from a sample. For this walkthrough, select the the "Thumbnail Creator" sample and choose Finish.

Once this function is deployed, it will get called when images are uploaded to an S3 bucket. The function will then resize the image into a thumbnail, and will upload the thumbnail to another bucket. The destination bucket for the thumbnail will be the same name as the bucket containing the original image plus a "-thumbnails" suffix.

The project will be set up containing three files and the dependent Node.js packages. This sample also has a dependency on the ImageMagick CLI, which you can download from Lambda has ImageMagick pre-configured on the compute instances that will be running the Lambda function.

Let’s take a look at the files added to the project.

app.js Defines the function that Lambda will invoke when it receives events.
_sampleEvent.json An example of what an event coming from S3 looks like.
_testdriver.js Utility code for executing the Lambda function locally. It will read in the _sampleEvent.json file and pass it into the Lambda function defined in app.js


To access AWS resources from Lamdba, functions use the AWS SDK for Node.js which has a different path for finding credentials than the AWS SDK for .NET. The AWS SDK for Node.js looks for credentials in the environment variables AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY or through the shared credentials file. For further information about configuring the AWS SDK for Node.js refer to the AWS SDK for Node.js documentation

Running locally

To run this sample, you will need to create the source and target S3 buckets. Pick a bucket name for the source bucket, and then create the bucket using AWS Explorer. Create a second bucket with the same name as the source bucket but with the "-thumbnails" suffix. For example, you could have a pair of buckets called foobar and foobar-thumbnails. Note: the _testdriver.js defaults the region to us-west-2, so be sure to update this to whatever region you create the buckets in. Once the buckets are created, upload an image to the source bucket so that you have an image to test with.

Open the _sampleEvent.js file and update the bucket name property to the source bucket and the object key property to the image that was uploaded.

Now, you can run and debug this like any other Visual Studio project. Go ahead and open up _testdriver.js and set a breakpoint and press F5 to launch the debugger.

Deploying the function to AWS Lambda

Once we have verified the function works correctly locally, it is time to deploy it. To do that, right-click on the project and select Upload to AWS Lambda….

This opens the Upload Lambda Function dialog.

You need to enter a Function Name to identify the function. You can leave the File Name and Handler fields at the default, which indicates what function to call on behalf of the event. You then need to configure an IAM role that Lambda can use to invoke your function. For this walkthrough, you are going to create a new role by selecting that we need Amazon S3 access and Amazon CloudWatch access. It is very useful to give access to CloudWatch so that Lambda can write debugging information to Amazon CloudWatch Logs and give you monitoring on the usage of the function. You can always refine these permissions after the function is uploaded. Once all that is set, go ahead and choose OK.

Once the upload is complete the Lambda Function status view will be displayed. The last step is to tell Amazon S3 to send events to your Lambda function. To do that, click the Add button for adding an event source.

Leave the Source Type set to Amazon S3 and select the Source bucket. S3 will need permission to send events to Lambda. This is done by assigning a role to the event source. By default, the dialog will create a role that gives S3 permission. Event sources to S3 are unique in that the configuration is actually done to the S3 bucket’s notification configuration. When you choose OK on this dialog, the event source will not show up here, but you can view it by right-clicking on the bucket and selecting properties.


Now that the function is deployed and S3 is configured to send events to our function, you can test it by uploading an image to the source bucket. Very shortly after uploading an image to the source bucket, your thumbnail will show up in the thumbnails bucket.


Calling from S3 Browser

Your function is set up to create thumbnails for any newly uploaded images. But what if you want to run our Lambda function on images that have already been uploaded? You can do that by opening the S3 bucket from AWS Explorer and navigating to the image you need the Lambda function to run against and choosing Invoke Lambda Function.

Next select the function we want to invoke and choose OK. The toolkit will then create the event object that S3 would have sent to Lambda and then calls Invoke on the function.

This can be done for an individual file or by selecting multiple files or folders in the S3 Browser. This is helpful when you make a code change to your Lambda function and you want to reprocess all the objects in your bucket with the new code.


Creating thumbnails is just one example you can use AWS Lambda for, but I’m sure you can imagine many ways you can use the power of Lambda’s event-based compute power. Currently, you can create event sources to Amazon S3, Amazon Kinesis, and Amazon DynamoDB Streams, which is currently in preview. It is also possible to invoke Lambda functions for your own custom events using any of AWS SDKs.

Try out the new Lambda features in the toolkit and let us know what you think. Given that AWS Lambda is in preview, we would love to get your feedback about these new features and what else we can add to make you successful using Lambda.