SYS ARCHITECTLearning Platform

Phase 1

  • Interview Framework
  • Back-of-the-Envelope Estimation
  • ACID
  • CAP
  • Consistency vs Integrity
  • Idempotency
  • NFR
  • SPOF
  • Stateless vs Stateful
  • SOLID
  • SRP
  • OCP
  • LSP
  • DIP vs LSP
  • Clear Architecture Principles
  • 12-Factor App

    • Phase 2

  • SQL vs NoSQL
  • Normalization vs Denormalization
  • Partition vs Sharding
  • Sharding
  • Partition Tolerance
  • Serializable Transactions
  • MVCC
  • Optimistic vs Pessimistic Locking
  • Row Level Locking
  • Distributed Locks
  • Redis Lock
  • Replication
  • Primary Replica Setup
  • Eventual Consistency
  • Data Consistency
  • Quorum
  • Write Ahead Logs
  • Redo Logs
  • DB Durability
  • Data Recovery
  • Two Phase Commit
  • Saga Pattern
  • Cassandra
  • S3
  • HDFS
  • Timeseries DB

    • Phase 3

  • Caching
  • Cache Eviction Policies
  • Hot Keys
  • Hot Reads and Writes
  • Latency
  • Latency vs Throughput
  • Tail Latency
  • Low Latency Patterns
  • Backpressure
  • Sudden Traffic Spike
  • Buffer Burst

    • Phase 4

  • Replication
  • Consistent Hashing
  • Leader Election
  • Distributed Locking
  • Fault Tolerance
  • Resiliency
  • Raft Consensus
  • Paxos
  • Event Driven Architecture
  • Event Sourcing
  • Outbox Pattern
  • CQRS

    • Phase 5

  • How HTTP Works
  • HTTP vs HTTPS
  • TCP vs UDP
  • TLS
  • Long Polling vs WebSockets
  • Server Sent Events
  • Load Balancer
  • L4 vs L7
  • Load Balancer vs Reverse Proxy vs API Gateway
  • CDN
  • Geo DNS

    • Phase 6

  • JWT
  • OAuth2
  • Opaque vs JWT Token
  • TLS
  • OWASP
  • Secrets Management

    • Phase 7

  • Creating Docker Image
  • Kubernetes ConfigMap
  • Kubernetes Ingress
  • Persistent Volume
  • Prometheus and Grafana

    • Phase 8

  • Monolith vs Microservices
  • API Gateway
  • Unique ID Generator
  • Retry Mechanism
  • Deployment Strategy
  • Rate Limiting

    • Phase 9

  • URL Shortener
  • Chat System
  • News Feed
  • Web Crawler
  • Notifications Design
  • System Design Problems
    • Settings
    Theory

    Layer 4 vs. Layer 7 Load Balancing

    📋 Overview

    Load balancing is the process of distributing network traffic across multiple servers. In the OSI model, this can happen at the Transport Layer (Layer 4) or the Application Layer (Layer 7). Choosing between L4 and L7 is a trade-off between the raw speed and efficiency of connection-level routing versus the intelligence and flexibility of content-aware routing.

    🏗️ Core Principles & Characteristics

    • Layer 4 (Transport):
      • Data Used: IP addresses and TCP/UDP ports.
      • Action: Forwards packets blindly without "looking inside" the data.
      • NAT: Uses Network Address Translation to redirect traffic.
    • Layer 7 (Application):
      • Data Used: HTTP headers, Cookies, URLs, and JSON payloads.
      • Action: Terminates the connection, parses the request, and makes a routing decision based on the content.

    ⚖️ Trade-offs: Pros & Cons

    • Layer 4 Pros:
      • Ultra-Fast: Minimal CPU overhead since it doesn't parse application data.
      • Protocol Agnostic: Works for any TCP/UDP service (MySQL, DNS, SMTP).
    • Layer 7 Pros:
      • Smart Routing: Can send /images to one server and /api to another.
      • Security: Can detect and block malicious payloads (WAF) or handle SSL termination.
      • Stickiness: More reliable "Sticky Sessions" based on cookies rather than just IP.

    🌍 Real-World Implementation

    • L4 Use Case: Handling massive, low-level traffic for a database cluster or a gaming server where latency is the #1 priority. (Tools: HAProxy, AWS NLB).
    • L7 Use Case: Modern microservices where different URL paths are served by different teams/pods. (Tools: Nginx, AWS ALB, Traefik).

    💡 Interview "Gotchas" & Tips

    • The "Termination" Point: L7 load balancers terminate the TCP connection, while L4 balancers just forward the packets. This means L7 is inherently a "Man-in-the-Middle."
    • Latency: L7 is slower because it has to wait for the full HTTP request to arrive before it can decide where to send it.
    • SSL Termination: If the LB handles SSL, it must be at least L7 (or L4 with SSL Passthrough) to read the encrypted headers.

    📐 Suggested Architecture Primitives

    • Network Load Balancer (NLB): For L4 high-throughput needs.
    • Application Load Balancer (ALB): For L7 feature-rich needs.
    • Reverse Proxy: The base technology for L7 balancing.
    • WAF (Web Application Firewall): Usually sits on top of an L7 balancer.
    Canvas