Become an AWS pro by learning to run serverless applications with AWS Lambda. Developed by AWS Solution Certified Architects. Get hands-on, no setup, no cleanup, no hassle.

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In the world of modern development, serverless computing has become table stakes. Serverless computing has seen a major uptake with AWS Lambda having an increased adoption of 667% in 2018. Companies are making the switch to serverless for shorter time to market and decreased operational costs, but for you the advantage lies in the ability to offload the burden of managing infrastructure to serverless platforms, so you can focus on building even better apps.

In this course, you will learn how to run serverless applications using AWS Lambda. You’ll start with the basics such as creating a web service where you’ll learn the steps to deploy an AWS Serverless Application Model (SAM). You’ll then move on to more advanced topics such as handling HTTP Requests, using external storage, and managing sessions and user workflows. By the end of this course, you will be ready to work with AWS Lambda in a professional setting, and you’ll have a great, transferable skill that employers will love to see.

Running Serverless Applications with AWS Lambda

## Another URL is required
In the previous chapter, you used the same URL for both the form display function and the form processing function. This was possible because the browser web form workflow used two different HTTP methods. To display the form, it sent a GET request. To upload the submission details, it sent a POST request. Because S3 redirects work as GET method calls, you cannot use the same URL with different methods anymore. The browser will send a POST request directly to S3, which will redirect to another URL. You'll need a different URL to handle that redirect, so you can create a new API endpoint.

When S3 sends a redirect after the upload, it will include information about the uploaded file in the query string. This allows you to do some post-processing on the uploaded file or to let the users access it. To keep things simple for now, just allow users to download a file they uploaded. In theory, you could read the file out using a Lambda function and send it back through API Gateway. By now, though, you know that there is a better way to handle that.
## Configuring access
S3 can serve public files directly to browsers. For example, public files in a bucket called `testbucket` in the `us-east-1` region will be accessible directly from `https://testbucket.s3.amazonaws.com`. For other regions, the second URL component is `s3-` followed by the region (for example `https://testbucket.s3-eu-west-1.amazonaws.com`). Letting users download files is a great option if you don't care about protecting read access, for example if you are making a public gallery. To upload publicly readable files, just change the access control list in the upload policy from `private` to `public-read` (line 19 in `show-form.js`).

To tightly control who can read the uploaded files, instead of a public link you can pre-sign a download request. A signed download request effectively provides a temporary grant to access a particular file on S3 directly. Similar to file uploads, directly downloading files from S3 is so common that the AWS SDK has a shortcut operation for it. You can use `s3.getSignedUrl` to sign generic S3 requests. You need to give it the related object key and the expiry time for the grant​ and specify the type of the S3 REST API operation. For retrieving objects, the REST API operation is called `getObject`. The signature method returns a URL with query string parameters prepared according to the authorised grant.

A new file is created in the Lambda code directory, called `confirm-upload.js`, using the following listing:



# Another URL is required
In the previous chapter, you used the same URL for both the form display function and the form processing function. This was possible because the browser web form workflow used two different HTTP methods. To display the form, it sent a GET request. To upload the submission details, it sent a POST request. Because S3 redirects work as GET method calls, you cannot use the same URL with different methods anymore. The browser will send a POST request directly to S3, which will redirect to another URL. You'll need a different URL to handle that redirect, so you can create a new API endpoint.

When S3 sends a redirect after the upload, it will include information about the uploaded file in the query string. This allows you to do some post-processing on the uploaded file or to let the users access it. To keep things simple for now, just allow users to download a file they uploaded. In theory, you could read the file out using a Lambda function and send it back through API Gateway. By now, though, you know that there is a better way to handle that.
# Configuring access
S3 can serve public files directly to browsers. For example, public files in a bucket called `testbucket` in the `us-east-1` region will be accessible directly from `https://testbucket.s3.amazonaws.com`. For other regions, the second URL component is `s3-` followed by the region (for example `https://testbucket.s3-eu-west-1.amazonaws.com`). Letting users download files is a great option if you don't care about protecting read access, for example if you are making a public gallery. To upload publicly readable files, just change the access control list in the upload policy from `private` to `public-read` (line 19 in `show-form.js`).

To tightly control who can read the uploaded files, instead of a public link you can pre-sign a download request. A signed download request effectively provides a temporary grant to access a particular file on S3 directly. Similar to file uploads, directly downloading files from S3 is so common that the AWS SDK has a shortcut operation for it. You can use `s3.getSignedUrl` to sign generic S3 requests. You need to give it the related object key and the expiry time for the grant​ and specify the type of the S3 REST API operation. For retrieving objects, the REST API operation is called `getObject`. The signature method returns a URL with query string parameters prepared according to the authorised grant.

A new file is created in the Lambda code directory, called `confirm-upload.js`, using the following listing:



In this lesson, you will learn how to sign download URLs and configure access to the files after they are uploaded. 

Signed Download URLs

Getting Started

Setup Tools for Local Development

Creating a Web Service

Host a Serverless Application on AWS Lambda

Development and Troubleshooting

Core Features of AWS Lambda

Handling HTTP Requests

Using External Storage

Cheaper, Faster, Serverless

Handling Platform Events

Using Application Components

Managing Sessions and User Workflows

Designing Robust Applications

Deployment Options

Process Amazon SNS Notifications with AWS Lambda

Signed Download URLs

Another URL is required #