API Gateway to DynamoDB - Mini Project: Build & Apply

API Gateway to DynamoDB

📖 Scenario: You are building a serverless REST API for a product catalog. Instead of using Lambda functions, you want API Gateway to connect directly to DynamoDB to reduce latency and cost. You need to create the request and response mapping templates for GET and POST operations.

🎯 Goal: Write the VTL mapping templates that transform HTTP requests into DynamoDB API calls and DynamoDB responses into clean JSON for the client.

📋 What You'll Learn

Create a GetItem request mapping template

Create a PutItem request mapping template

Write a response mapping for GetItem that strips DynamoDB type descriptors

Add error handling for missing items

💡 Why This Matters

🌍 Real World

Direct API Gateway to DynamoDB integration is used in high-performance serverless APIs where simple CRUD operations don't need Lambda compute overhead.

💼 Career

AWS developers use this pattern to build cost-effective APIs for catalogs, configurations, and metadata services that need sub-50ms response times.

1

GetItem request mapping template

Create a JSON request mapping template for GET /products/{id}. Set TableName to "Products" and Key to an object with "id" of type "S" using $input.params('id') to read the path parameter.

DynamoDB

// GET /products/{id} → DynamoDB GetItem
// Request mapping template:
// Your code here

Hint

DynamoDB GetItem needs TableName and Key. The key value uses type descriptor S for strings.

2

PutItem request mapping template

Create a JSON request mapping template for POST /products. Set TableName to "Products" and Item with three fields: "id" (type "S") from $input.path('$.id'), "name" (type "S") from $input.path('$.name'), and "price" (type "N") from $input.path('$.price').

DynamoDB

// POST /products → DynamoDB PutItem
// Request mapping template:
// Your code here

Hint

Use $input.path('$.field') to read JSON body fields. Numbers use type N, strings use S.

3

GetItem response mapping template

Write a VTL response mapping template that extracts the item from $input.path('$.Item') into a variable $item using #set, then returns a JSON object with id from $item.id.S, name from $item.name.S, and price from $item.price.N (without quotes for the number).

DynamoDB

// GetItem response mapping template:
// Transform DynamoDB typed JSON to clean JSON
// Your code here

Hint

Use #set to assign the item, then access typed values like $item.id.S. Leave numbers unquoted.

4

Add error handling for missing items

Wrap the response template in a VTL conditional. Check if $input.path('$.Item') is empty using #if($input.path('$.Item') == ''). If empty, set the response status to 404 with #set($context.responseOverride.status = 404) and return {"error": "Product not found"}. Otherwise return the normal mapped response from step 3.

DynamoDB

// GetItem response with error handling:
// Check if item exists, return 404 if not
// Your code here

Hint

Use #if/#else/#end for conditional logic. Override the HTTP status with $context.responseOverride.status.

Practice

1. What is the primary role of API Gateway when used with DynamoDB?

easy

A. To replace DynamoDB as a database

B. To store data directly in DynamoDB

C. To securely expose DynamoDB operations over HTTP

D. To perform complex data analytics on DynamoDB data

Solution

1. Step 1: Understand API Gateway's function

   API Gateway acts as a secure interface that translates HTTP requests into backend service calls.

2. Step 2: Identify its role with DynamoDB

   It exposes DynamoDB operations securely over HTTP, enabling controlled access and monitoring.

3. Final Answer:

   To securely expose DynamoDB operations over HTTP -> Option C

4. Quick Check:

   API Gateway = Secure HTTP access to DynamoDB [OK]

Hint: API Gateway acts as a secure HTTP front for DynamoDB [OK]

Common Mistakes:

• Thinking API Gateway stores data
• Confusing API Gateway with DynamoDB itself
• Assuming API Gateway performs data analytics

2. Which of the following is the correct way to define a GET method in API Gateway to fetch an item from DynamoDB?

easy

A. Use HTTP GET with a path parameter for the key and integrate with DynamoDB GetItem action

B. Use HTTP POST with a JSON body containing the key and integrate with DynamoDB PutItem action

C. Use HTTP DELETE with query parameters and integrate with DynamoDB DeleteItem action

D. Use HTTP PUT with path parameters and integrate with DynamoDB UpdateItem action

Solution

1. Step 1: Match HTTP method to DynamoDB action

   GET method is used to retrieve data, so it should map to DynamoDB's GetItem action.

2. Step 2: Use path parameter for key

   The key identifying the item is passed as a path parameter in the GET request.

3. Final Answer:

   Use HTTP GET with a path parameter for the key and integrate with DynamoDB GetItem action -> Option A

4. Quick Check:

   GET + path key = GetItem [OK]

Hint: GET method fetches data; use path parameter for key [OK]

Common Mistakes:

• Using POST instead of GET for fetching
• Confusing PutItem with GetItem
• Using wrong HTTP methods for actions

3. Given this API Gateway integration request mapping template snippet:

{
  "TableName": "Users",
  "Key": {
    "UserId": { "S": "$input.params('userId')" }
  }
}

What DynamoDB operation does this template prepare for?

medium

A. PutItem to insert a new user

B. GetItem to fetch a user by UserId

C. DeleteItem to remove a user

D. UpdateItem to modify user attributes

Solution

1. Step 1: Analyze the template structure

   The template specifies a TableName and a Key with UserId, which matches the input for a GetItem request.

2. Step 2: Match to DynamoDB operation

   GetItem requires TableName and Key to fetch an item; PutItem or UpdateItem would include Item or UpdateExpression fields.

3. Final Answer:

   GetItem to fetch a user by UserId -> Option B

4. Quick Check:

   TableName + Key = GetItem [OK]

Hint: TableName + Key in template means GetItem [OK]

Common Mistakes:

• Confusing GetItem with PutItem
• Assuming DeleteItem without DeleteExpression
• Ignoring the Key field meaning

4. You configured API Gateway to integrate with DynamoDB PutItem but receive a 400 Bad Request error. Which of these is the most likely cause?

medium

A. Missing required 'Item' field in the request mapping template

B. Using HTTP GET method instead of POST

C. Incorrect table name in the DynamoDB action

D. Not enabling CORS on API Gateway

Solution

1. Step 1: Understand PutItem requirements

   PutItem requires an 'Item' field specifying the data to insert; missing it causes a bad request.

2. Step 2: Evaluate other options

   Using GET instead of POST may cause issues but usually not 400 if mapping is correct; wrong table name causes 500 errors; CORS issues cause client-side errors, not 400 from API Gateway.

3. Final Answer:

   Missing required 'Item' field in the request mapping template -> Option A

4. Quick Check:

   PutItem needs 'Item' field [OK]

Hint: PutItem must include 'Item' in request template [OK]

Common Mistakes:

• Confusing HTTP method errors with mapping errors
• Ignoring required fields in request templates
• Assuming CORS causes 400 errors

5. You want to design a scalable API Gateway to DynamoDB system that supports thousands of requests per second with minimal latency. Which combination of design choices is best?

hard

A. Use API Gateway without caching, DynamoDB with provisioned capacity, and open access without authentication

B. Use API Gateway with caching disabled, DynamoDB with manual scaling, and no monitoring enabled

C. Use API Gateway with throttling disabled, DynamoDB with global tables disabled, and API keys for access control

D. Use API Gateway with caching enabled, DynamoDB with on-demand capacity mode, and IAM roles for secure access

Solution

1. Step 1: Choose scalable DynamoDB capacity mode

   On-demand capacity mode automatically scales to handle high request volumes without manual intervention.

2. Step 2: Enable API Gateway caching and secure access

   Caching reduces latency and load on DynamoDB; IAM roles provide secure, managed access.

3. Step 3: Avoid options that disable throttling or monitoring

   Disabling throttling or monitoring risks overload and lack of visibility; open access is insecure.

4. Final Answer:

   Use API Gateway with caching enabled, DynamoDB with on-demand capacity mode, and IAM roles for secure access -> Option D

5. Quick Check:

   Caching + on-demand + IAM = scalable & secure [OK]

Hint: Enable caching and on-demand capacity for scalability [OK]

Common Mistakes:

• Disabling throttling causing overload
• Using provisioned capacity without scaling
• Ignoring security best practices