Welcome to the wonderful world of AWS API Gateway! In this article, we'll be discussing what API Gateway is, how it can be used, and how to use API Gateway VTL Mapping Templates to transform your API requests and responses.

Introduction

So, what is AWS API Gateway? Simply put, it is a fully managed service that makes it easy for developers to create, publish, maintain, monitor, and secure APIs at any scale. API Gateway handles all of the tasks involved in accepting and processing API requests, including traffic management, authorization and access control, monitoring, and API version management.

One of the key features of API Gateway is the ability to transform API requests and responses using VTL (Velocity Template Language) Mapping Templates. VTL is a simple, powerful language that allows you to manipulate the data in your API requests and responses in a variety of ways. For example, you might use VTL to extract specific values from a request, add or remove fields from a response, or even invoke other AWS services.

To use VTL Mapping Templates in API Gateway, you'll first need to define a "template" that specifies how you want to transform the request or response. You can then specify this template in the API Gateway configuration for a particular API method. When a request is made to that method, API Gateway will automatically execute the template and apply the transformation to the request or response.

Use Cases

So, why might you want to use VTL Mapping Templates? There are many possible use cases, but here are a few examples:

• Data transformation: You might use VTL to extract specific values from a request and use them to create a new request to another API, or to transform a response from one format to another.
• Conditional logic: VTL includes support for basic conditional statements, so you can use templates to apply different transformations based on the contents of the request or response.
• Invoking other AWS services: VTL includes built-in support for invoking other AWS services, so you can use templates to trigger Lambda functions, send messages to SNS topics, and more.

Examples

Now that you have a basic understanding of what API Gateway is and how VTL Mapping Templates can be used, let's take a look at a simple example. Suppose we have an API that receives a POST request with a JSON payload containing a customer name and address. We want to use this information to create a new customer record in a database, so we need to extract the name and address from the request and send them to the database.

To do this, we'll use a VTL Mapping Template to extract the name and address from the request and create a new JSON payload containing just those fields. We'll then use another template to send this payload to the database using the AWS SDK for Java.

Here's what the VTL Mapping Template for extracting the name and address from the request might look like:

#set($inputRoot = $input.path('$'))
{
  "name": "$inputRoot.name",
  "address": "$inputRoot.address"
}

And here's the template for sending the payload to the database:

#set($sdk = $util.import("com.amazonaws.util.IOUtils"))
#set($json = $sdk.toJsonString($input))
#set($dbClient = $util.getAwsClient("rds", ["us-east-1"]))

{
  "operation": "putItem",
  "tableName": "customers,
  "item": $json
}

To use these templates, we would define them in the API Gateway configuration for the relevant API method, and API Gateway would automatically execute them whenever a request is made to that method.

Conclusion

That's just a basic example of how you can use VTL Mapping Templates in API Gateway, but the possibilities are virtually endless. With VTL, you can create complex transformations and integrations with other AWS services, all within the easy-to-use API Gateway interface.

We hope this introduction to AWS API Gateway and VTL Mapping Templates has been helpful, and we encourage you to start exploring these powerful tools for yourself. Whether you're building a simple API for your own applications or a complex, multi-faceted integration platform, API Gateway has the features and functionality you need to succeed. Happy coding!