Lambda pricing model in AWS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What are the two main factors that determine AWS Lambda pricing?

AWS Lambda pricing is mainly based on the number of requests and the duration of code execution measured in GB-seconds.

beginner

How does AWS Lambda measure the duration for billing?

Duration is measured from the time your code begins executing until it returns or otherwise terminates, rounded up to the nearest 1 millisecond.

intermediate

What is a GB-second in AWS Lambda pricing?

A GB-second is the amount of memory allocated to your function multiplied by the execution time in seconds. For example, 1 GB of memory running for 1 second equals 1 GB-second.

beginner

Does AWS Lambda charge for idle time when your function is not running?

No, AWS Lambda only charges for the actual compute time your function runs, not for idle time.

beginner

What is the AWS Lambda free tier offer?

AWS Lambda offers 1 million free requests and 400,000 GB-seconds of compute time per month at no charge.

Which of the following does NOT affect AWS Lambda pricing?

A Number of concurrent users accessing your website

B Execution duration

C Amount of memory allocated

D Number of requests

AWS Lambda pricing depends on requests, execution duration, and memory allocated, not on website user count.

How is the execution duration rounded for billing in AWS Lambda?

A To the nearest second

B To the nearest 100 milliseconds

C To the nearest 1 millisecond

D To the nearest minute

AWS Lambda rounds execution duration up to the nearest 1 millisecond for billing.

What does 1 GB-second represent in AWS Lambda pricing?

A 1 GB of storage used for 1 second

B 1 GB of CPU usage for 1 second

C 1 GB of network bandwidth used for 1 second

D 1 GB of memory used for 1 second

1 GB-second means your function used 1 GB of memory for 1 second of execution time.

What is included in the AWS Lambda free tier each month?

A 500,000 requests and 200,000 GB-seconds

B 1 million requests and 400,000 GB-seconds

C Unlimited requests and 100,000 GB-seconds

D 1 million requests and unlimited GB-seconds

The free tier includes 1 million requests and 400,000 GB-seconds of compute time monthly.

Does AWS Lambda charge for the time your function is waiting (idle) between executions?

A No, only for actual execution time

B Only during peak hours

C Yes, always

D Only if memory is above 1 GB

AWS Lambda charges only for the actual time your function runs, not for idle waiting time.

Explain how AWS Lambda pricing works including the main factors that affect cost.

Think about what AWS counts and charges you for when your function runs.

Describe what a GB-second means in the context of AWS Lambda and why it matters for pricing.

Consider how memory and time combine to form the billing metric.

Practice

1. What two main factors determine the cost of an AWS Lambda function?

easy

A. Number of requests and compute time

B. Storage size and network bandwidth

C. Number of users and API calls

D. Memory size and database queries

Solution

1. Step 1: Understand AWS Lambda pricing basics

   AWS Lambda charges based on how many times your function runs (requests) and how long it runs (compute time).

2. Step 2: Identify the pricing factors

   Memory size affects compute time cost but the main factors are requests and compute time.

3. Final Answer:

   Number of requests and compute time -> Option A

4. Quick Check:

   Requests + compute time = cost [OK]

Hint: Remember: pay for calls and duration only [OK]

Common Mistakes:

• Confusing storage or bandwidth as pricing factors
• Thinking memory size alone determines cost
• Mixing API calls with requests

2. Which of the following is the correct way to express AWS Lambda pricing units?

easy

A. Memory in MB and network packets

B. Requests per hour and CPU cycles

C. Number of requests and GB-seconds

D. Storage in GB and function calls

Solution

1. Step 1: Recall AWS Lambda pricing units

   Lambda pricing is based on number of requests and compute time measured in GB-seconds (memory size x execution time).

2. Step 2: Match correct units

   Requests count how many times function runs; GB-seconds measure memory used over time.

3. Final Answer:

   Number of requests and GB-seconds -> Option C

4. Quick Check:

   Requests + GB-seconds = pricing units [OK]

Hint: Think requests and memory-time units [OK]

Common Mistakes:

• Using CPU cycles or network packets incorrectly
• Confusing storage with compute time
• Mixing units like MB with packets

3. If a Lambda function runs 1,000,000 times with 512 MB memory for 1 second each, which factor mainly increases the cost?

medium

A. Execution time of 1 second per request

B. Network bandwidth used by the function

C. Memory size doubling from 256 MB to 512 MB

D. Number of requests being 1,000,000

Solution

1. Step 1: Understand cost components

   Cost depends on requests and GB-seconds (memory size x execution time x requests).

2. Step 2: Analyze impact of memory size

   Doubling memory from 256 MB to 512 MB doubles GB-seconds, increasing cost significantly, but the number of requests (1,000,000) is the main driver of total cost.

3. Final Answer:

   Number of requests being 1,000,000 -> Option D

4. Quick Check:

   Requests x GB-seconds = total cost [OK]

Hint: Number of requests greatly impacts total cost [OK]

Common Mistakes:

• Ignoring number of requests effect
• Thinking network bandwidth affects Lambda cost
• Assuming execution time or memory alone drives cost

4. A developer notices their Lambda cost is higher than expected. They set memory to 1024 MB but function runs only 100 ms. What is the likely issue?

medium

A. Memory size is too high for short execution time

B. Number of requests is too low

C. Function execution time is too long

D. Free tier is not applied to this function

Solution

1. Step 1: Review memory and execution time relation

   Cost depends on memory size multiplied by execution time. High memory with short time still costs more than lower memory.

2. Step 2: Identify cost cause

   Setting memory to 1024 MB increases GB-seconds cost even if function runs only 100 ms.

3. Final Answer:

   Memory size is too high for short execution time -> Option A

4. Quick Check:

   High memory + short time can increase cost [OK]

Hint: High memory with short run still costs more [OK]

Common Mistakes:

• Assuming short execution time always means low cost
• Ignoring memory size impact
• Thinking free tier always applies

5. A company uses Lambda functions with 256 MB memory running 200 ms per request. They want to reduce cost without changing code. Which approach helps most?

hard

A. Switch to EC2 instances for better pricing

B. Reduce memory size to 128 MB if function still runs correctly

C. Increase number of requests to use free tier fully

D. Increase memory size to reduce execution time

Solution

1. Step 1: Understand cost relation to memory and time

   Cost = requests x memory size x execution time. Reducing memory lowers GB-seconds cost if function still works.

2. Step 2: Evaluate options

   Reducing memory to 128 MB saves cost if performance is acceptable. Increasing memory or requests raises cost. Switching to EC2 is a different model and may not be cheaper.

3. Final Answer:

   Reduce memory size to 128 MB if function still runs correctly -> Option B

4. Quick Check:

   Lower memory reduces GB-seconds cost [OK]

Hint: Lower memory if function still works to save cost [OK]

Common Mistakes:

• Increasing memory without checking cost impact
• Thinking more requests reduce cost
• Assuming EC2 always cheaper than Lambda