Resources and methods in AWS - Time & Space Complexity

Time Complexity: Resources and methods

O(n)

Understanding Time Complexity

When working with AWS resources and methods, it's important to understand how the time to complete tasks grows as you add more resources or methods.

We want to know how the number of API calls or operations changes when we increase resources or methods.

Scenario Under Consideration

Analyze the time complexity of creating multiple resources and attaching methods to them.

for resource_name in resource_list:
    resource = api_gateway.create_resource(restApiId=api_id, parentId=parent_id, pathPart=resource_name)
    api_gateway.put_method(restApiId=api_id, resourceId=resource['id'], httpMethod='GET', authorizationType='NONE')
    

This sequence creates a resource for each name and adds a GET method to it.

Identify Repeating Operations

• Primary operation: Creating a resource and adding a method for each item.
• How many times: Once per resource in the list.

How Execution Grows With Input

Each new resource requires one create call and one method call.

Input Size (n)	Approx. Api Calls/Operations
10	20 (10 creates + 10 methods)
100	200 (100 creates + 100 methods)
1000	2000 (1000 creates + 1000 methods)

Pattern observation: The number of API calls grows directly with the number of resources.

Final Time Complexity

Time Complexity: O(n)

This means the time to complete grows in a straight line as you add more resources.

Common Mistake

[X] Wrong: "Adding more methods to the same resource does not increase the number of API calls significantly."

[OK] Correct: Each method requires its own API call, so adding methods increases calls linearly with the number of methods.

Interview Connect

Understanding how operations scale with resources helps you design efficient cloud setups and shows you can think about costs and delays realistically.

Self-Check

"What if we batch create resources instead of one by one? How would the time complexity change?"

Practice

1. What does a resource represent in AWS API Gateway?

easy

A. A URL path that clients can access

B. A backend database connection

C. A security policy for API access

D. A method to deploy the API

Solution

1. Step 1: Understand the role of resources in API Gateway

   Resources define the URL paths that clients use to reach your API endpoints.

2. Step 2: Differentiate resources from other components

   Resources are not backend connections, security policies, or deployment methods; they are URL paths.

3. Final Answer:

   A URL path that clients can access -> Option A

4. Quick Check:

   Resource = URL path [OK]

Hint: Resources are the API's URL paths clients call [OK]

Common Mistakes:

• Confusing resources with backend services
• Thinking resources are security settings
• Mixing resources with deployment steps

2. Which HTTP method is correctly defined in AWS API Gateway to retrieve data?

easy

A. GET

B. POST

C. DELETE

D. PUT

Solution

1. Step 1: Identify the HTTP method for data retrieval

   GET is the standard HTTP method used to retrieve or read data from a resource.

2. Step 2: Confirm other methods' purposes

   POST creates data, DELETE removes data, and PUT updates data, so they are not for retrieval.

3. Final Answer:

   GET -> Option A

4. Quick Check:

   GET = retrieve data [OK]

Hint: GET method is for reading data from resources [OK]

Common Mistakes:

• Using POST instead of GET to fetch data
• Confusing DELETE with data retrieval
• Mixing PUT with GET for reading data

3. Given this API Gateway setup: a resource /items with a POST method integrated to a Lambda function. What happens when a client sends a POST request to /items?

medium

A. The API Gateway returns a static mock response

B. The API Gateway returns a 404 Not Found error

C. The Lambda function is triggered to process the request

D. The request is ignored because POST is not allowed

Solution

1. Step 1: Understand the integration of POST method with Lambda

   The POST method on the /items resource is connected to a Lambda function, so requests trigger that function.

2. Step 2: Analyze the client request effect

   When a client sends a POST request to /items, API Gateway forwards it to Lambda for processing.

3. Final Answer:

   The Lambda function is triggered to process the request -> Option C

4. Quick Check:

   POST + Lambda integration = Lambda triggered [OK]

Hint: POST method triggers Lambda if integrated [OK]

Common Mistakes:

• Assuming POST is not allowed without checking method setup
• Thinking API Gateway returns 404 if resource exists
• Confusing mock responses with Lambda integration

4. You created a resource /users and added a GET method, but clients get a 403 Forbidden error when calling it. What is the most likely cause?

medium

A. The client is using POST instead of GET

B. The resource path is misspelled

C. The API Gateway is not deployed

D. The method does not have an integration configured

Solution

1. Step 1: Check method integration setup

   A 403 Forbidden often means the method exists but lacks proper integration or permissions.

2. Step 2: Rule out other causes

   If the resource path was misspelled, the error would be 404. If API Gateway was not deployed, the error would differ. Using POST instead of GET would cause a 405 Method Not Allowed.

3. Final Answer:

   The method does not have an integration configured -> Option D

4. Quick Check:

   403 Forbidden = missing integration or permissions [OK]

Hint: 403 often means method lacks integration or permissions [OK]

Common Mistakes:

• Confusing 403 with 404 or 405 errors
• Ignoring deployment status
• Assuming client method is always correct

5. You want to create an API with a resource /orders that supports both GET and POST methods. The GET method returns a mock response, and the POST method triggers a Lambda function. Which configuration correctly sets this up?

hard

A. Create /orders resource; add GET and POST methods both with MOCK integration

B. Create /orders resource; add GET method with MOCK integration; add POST method with Lambda integration

C. Create /orders resource; add GET method with Lambda integration; add POST method with MOCK integration

D. Create /orders resource; add GET and POST methods both with Lambda integration

Solution

1. Step 1: Match method to integration type

   The GET method should use MOCK integration to return a static response without backend calls.

2. Step 2: Configure POST method to trigger Lambda

   The POST method must be integrated with Lambda to process incoming data.

3. Step 3: Verify the correct combination

   Create /orders resource; add GET method with MOCK integration; add POST method with Lambda integration correctly assigns MOCK to GET and Lambda to POST on the /orders resource.

4. Final Answer:

   Create /orders resource; add GET method with MOCK integration; add POST method with Lambda integration -> Option B

5. Quick Check:

   GET=MOCK, POST=Lambda [OK]

Hint: GET with MOCK, POST with Lambda for mixed behavior [OK]

Common Mistakes:

• Swapping MOCK and Lambda integrations between methods
• Using same integration for both methods incorrectly
• Forgetting to create the resource before methods