Quick Reference Guide for Amazon L6/L7 Interviews¶

🚀 Interview Day Cheat Sheet¶

Pre-Interview Checklist¶

📊 Key Numbers to Memorize¶

System Scale Metrics¶

Python
# Latency Numbers Every Engineer Should Know (2024)
L1_cache_reference = 0.5  # ns
Branch_mispredict = 5  # ns  
L2_cache_reference = 7  # ns
Mutex_lock_unlock = 25  # ns
Main_memory_reference = 100  # ns
Send_1KB_over_1Gbps = 10_000  # ns (10 μs)
SSD_random_read = 150_000  # ns (150 μs)
Read_1MB_from_SSD = 1_000_000  # ns (1 ms)
HDD_seek = 10_000_000  # ns (10 ms)
Read_1MB_from_HDD = 20_000_000  # ns (20 ms)
Send_packet_CA_to_Netherlands = 150_000_000  # ns (150 ms)

AWS Service Limits¶

Service	Key Limits	Notes
DynamoDB	40K RCU/WCU per table	Auto-scaling available
S3	3.5K PUT/POST/DELETE per prefix	5.5K GET/HEAD
Lambda	15 min timeout, 10GB memory	1000 concurrent default
SQS	256KB message size	14 days retention
API Gateway	10K requests/sec	29 sec timeout
EC2	20 instances default	Increasable via support

Capacity Planning¶

Python
# Quick Estimations
1M requests/day = ~12 requests/second
1B requests/month = ~400 requests/second
1 photo (compressed) = ~200KB
1 minute HD video = ~50MB
1TB = 1000GB = 1_000_000MB

🏗️ System Design Template¶

1. Requirements (5 min)¶

Markdown
Functional:
- Feature 1: [Description]
- Feature 2: [Description]

Non-Functional:
- Users: [Number]
- Requests: [QPS]
- Latency: [p50/p99]
- Availability: [99.9% or 99.99%]
- Data: [Volume]

2. Capacity Estimation (3 min)¶

Python
users = 100_000_000
daily_active = users * 0.1
requests_per_user = 10
total_requests = daily_active * requests_per_user
qps = total_requests / 86400
peak_qps = qps * 3  # 3x for peak

3. High-Level Design (10 min)¶

Text Only
1 2 3 4 5	`[Client] --> [CDN] --> [LB] --> [API Gateway] \| [Service Layer] \| [Cache] <-- [Database]`

4. Detailed Components (15 min)¶

API Design
Data Model
Algorithm Choice
Service Breakdown

5. Scale & Optimize (10 min)¶

Caching Strategy
Database Sharding
Load Balancing
CDN Usage

6. Handle Failures (5 min)¶

Single points of failure
Data loss scenarios
Network partitions
Cascading failures

💻 Coding Patterns Quick Reference¶

Two Pointers¶

Python
def two_sum_sorted(arr, target):
    left, right = 0, len(arr) - 1
    while left < right:
        curr_sum = arr[left] + arr[right]
        if curr_sum == target:
            return [left, right]
        elif curr_sum < target:
            left += 1
        else:
            right -= 1
    return []

Sliding Window¶

Python
def max_sum_subarray(arr, k):
    window_sum = sum(arr[:k])
    max_sum = window_sum

    for i in range(k, len(arr)):
        window_sum = window_sum - arr[i-k] + arr[i]
        max_sum = max(max_sum, window_sum)

    return max_sum

BFS Template¶

Python
from collections import deque

def bfs(root):
    if not root:
        return

    queue = deque([root])
    visited = set([root])

    while queue:
        node = queue.popleft()
        # Process node
        for neighbor in node.neighbors:
            if neighbor not in visited:
                visited.add(neighbor)
                queue.append(neighbor)

DFS Template¶

Python
def dfs(node, visited=None):
    if visited is None:
        visited = set()

    visited.add(node)
    # Process node

    for neighbor in node.neighbors:
        if neighbor not in visited:
            dfs(neighbor, visited)

    return visited

Binary Search¶

Python
def binary_search(arr, target):
    left, right = 0, len(arr) - 1

    while left <= right:
        mid = left + (right - left) // 2
        if arr[mid] == target:
            return mid
        elif arr[mid] < target:
            left = mid + 1
        else:
            right = mid - 1

    return -1

🎭 STAR Story Template¶

For comprehensive guidance: STAR Framework Mastery Guide

Quick STAR Format¶

Markdown

S: At [Company], our [system] was experiencing [problem]
   affecting [X users/$ impact].

T: As [role], I needed to [objective] within [constraints].

A: I [action 1], [action 2], and [action 3].
   Specifically, I [technical detail] and [leadership action].

R: This resulted in [metric improvement], saving [$X] and
   improving [customer metric]. I learned [lesson].

🎯 Leadership Principles Quick Guide¶

Most Important for L6¶

Deliver Results - Show consistent execution
Ownership - Take end-to-end responsibility
Dive Deep - Demonstrate technical depth
Earn Trust - Build team relationships
Learn and Be Curious - Show growth mindset

Most Important for L7¶

Think Big - Demonstrate vision
Invent and Simplify - Show innovation
Are Right, A Lot - Strategic decisions
Have Backbone - Influence upward
Hire and Develop - Build organizations

🔧 AWS Services Quick Reference¶

Compute¶

EC2: Virtual servers
Lambda: Serverless functions
ECS/EKS: Container orchestration

Storage¶

S3: Object storage
EBS: Block storage
EFS: File storage

Database¶

RDS: Relational (MySQL, PostgreSQL)
DynamoDB: NoSQL key-value
ElastiCache: In-memory cache
Redshift: Data warehouse

Networking¶

VPC: Virtual private cloud
CloudFront: CDN
Route 53: DNS
API Gateway: API management

Messaging¶

SQS: Queue service
SNS: Pub/sub notifications
EventBridge: Event bus
Kinesis: Stream processing

📝 Common Behavioral Questions¶

L6 Level¶

Tell me about a time you disagreed with your manager
Describe a situation where you had to make a decision with incomplete information
How did you handle an underperforming team member?
Give an example of when you failed
Describe your most challenging technical project

L7 Level¶

How did you drive organizational change?
Describe influencing a decision at VP level
Tell me about building a platform used by multiple teams
How did you handle competing priorities from different VPs?
Describe creating a multi-year technical strategy

⚡ Time Management Tips¶

Coding Interview (45 min)¶

0-5 min: Understand problem
5-10 min: Discuss approach
10-30 min: Code solution
30-35 min: Test and debug
35-40 min: Optimize
40-45 min: Questions

System Design (60 min)¶

0-5 min: Requirements
5-10 min: Estimation
10-25 min: High-level design
25-45 min: Deep dive
45-55 min: Scale and optimize
55-60 min: Wrap up

Behavioral (45 min)¶

0-5 min: Introduction
5-40 min: 3-4 STAR stories
40-45 min: Your questions

🚨 Red Flags to Avoid¶

Technical¶

❌ Over-engineering simple problems
❌ Ignoring requirements
❌ Not considering trade-offs
❌ Forgetting about failures
❌ No cost consideration

Behavioral¶

❌ Blaming others
❌ No quantified results
❌ Theoretical examples
❌ Not showing growth
❌ Weak leadership examples

Communication¶

❌ Not asking questions
❌ Rambling answers
❌ Getting defensive
❌ Not thinking out loud
❌ Poor time management

✅ Success Formulas¶

System Design Success¶

Text Only
1 2 3 4 5	`Success = Clear Communication + Structured Approach + Trade-off Analysis + Scale Considerations + Practical Experience`

Coding Success¶

Text Only
1 2 3 4 5	`Success = Problem Understanding + Clean Code + Optimal Algorithm + Edge Cases + Clear Explanation`

Behavioral Success¶

Text Only
1 2 3 4 5	`Success = Relevant Stories + STAR Structure + Quantified Impact + Leadership Principles + Self-Reflection`

🎯 Final Interview Tips¶

Be yourself - Authenticity matters
Think out loud - Share your process
Ask questions - Show curiosity
Stay calm - Mistakes are okay
Be specific - Use real examples
Show impact - Quantify results
Demonstrate growth - Learn from failures
Prepare questions - Show interest

📞 Questions to Ask Interviewers¶

About the Role¶

What are the biggest challenges facing this team?
What does success look like in this role?
How is the team structured?

About the Team¶

What's the team's tech stack?
How do you handle on-call?
What's the team culture like?

About Growth¶

What learning opportunities are available?
How is performance evaluated?
What's the path to L7/L8?

You're Ready!

Keep this guide handy during your preparation and review it the night before your interview. Remember: you've prepared thoroughly, trust your preparation, and show them what you can do!

Good luck with your interview! 🚀