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

    Geo-DNS: Location-Aware Routing

    📋 Overview

    Geo-DNS is a DNS resolution technique that returns different IP addresses based on the geographic location of the client. It is a critical component of Global Server Load Balancing (GSLB), used to reduce network latency by directing users to the data center physically closest to them, and to comply with regional data regulations.

    🏗️ Core Principles & Characteristics

    • IP Geolocation: The DNS server identifies the client's country, state, or city using an IP-to-location database.
    • EDNS Client Subnet (ECS): A protocol extension that allows the DNS resolver to pass a portion of the user's actual IP to the Geo-DNS server, ensuring accuracy even when using third-party resolvers (like Google DNS).
    • Traffic Steering: Routing traffic based on business rules (e.g., "Send all UK traffic to the London cluster").
    • Latency-Based Routing: An advanced form of Geo-DNS that chooses the center with the lowest measured network latency, rather than just the shortest physical distance.

    ⚖️ Trade-offs: Pros & Cons

    • Pros:
      • Low Latency: Significant reduction in "Time to First Byte" for global users.
      • Regulatory Compliance: Helps keep data within specific borders (e.g., GDPR/EU data).
      • Availability: Acts as a failover mechanism; if the "US-East" region fails, users can be routed to "US-West."
    • Cons:
      • Caching Issues: DNS records are cached by ISPs and browsers; updates are not instantaneous (TTL delay).
      • Inaccuracy: VPNs and proxies can hide a user's true location, leading to sub-optimal routing.
      • Complexity: Managing global IP ranges and health checks adds operational overhead.

    🌍 Real-World Implementation

    • Content Delivery Networks (CDNs): (Cloudflare, Akamai) use Geo-DNS to point users to the nearest "Edge" node.
    • Netflix/YouTube: Route users to local caches (OpenConnect) to stream heavy video data without crossing oceans.
    • AWS Route53: Offers "Geolocation Routing" and "Latency Routing" policies as managed services.

    💡 Interview "Gotchas" & Tips

    • The Resolver Problem: Explain that without ECS, the DNS server only sees the IP of the ISP's resolver, not the user.
    • Geo-DNS vs. Anycast: Know the difference. Anycast (BGP) is faster but gives less control than Geo-DNS.
    • Low TTL: Why use it? (Answer: To ensure fast failover and accurate routing changes).
    • Regulatory Fencing: How do you ensure German data stays in Germany? (Answer: Geo-DNS + Geo-fencing at the application layer).

    📐 Suggested Architecture Primitives

    • Anycast IP: For initial entry points.
    • Geo-DNS Records: With low TTL (e.g., 60-300 seconds).
    • EDNS-Enabled Resolvers: For accurate geolocation.
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