Protocol & Design Interview Questions - Medium

calendarDec 13, 2025 · 2 min read · protocol interview medium distributed-systems  ·
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Medium-level protocol and design interview questions covering advanced networking and distributed systems concepts.

Q1: Explain HTTP/2 improvements over HTTP/1.1.

Answer:

HTTP/1.1 vs HTTP/2

Multiplexing

Benefits:

  • No head-of-line blocking
  • Reduced latency
  • Better bandwidth utilization
  • Fewer connections

Q2: Explain gRPC and Protocol Buffers.

Answer:

gRPC Communication Types

Unary RPC

Server Streaming

Protocol Buffers

Advantages over REST/JSON:

  • Smaller payload (binary)
  • Faster serialization
  • Strong typing
  • Backward compatibility
  • Streaming support

Q3: Explain distributed consensus (Raft/Paxos basics).

Answer:

Raft Overview

Leader Election

Log Replication

Use Cases:

  • Distributed databases (etcd, Consul)
  • Coordination services
  • Configuration management

Q4: Explain message queues and pub/sub patterns.

Answer:

Point-to-Point Queue

Publish-Subscribe

Message Flow

Benefits:

  • Decoupling: Producers/consumers independent
  • Buffering: Handle traffic spikes
  • Reliability: Messages persisted
  • Scalability: Add consumers

Use Cases:

  • Task queues (background jobs)
  • Event streaming
  • Log aggregation
  • Microservice communication

Q5: Explain idempotency in distributed systems.

Answer:

Idempotent vs Non-Idempotent

Making POST Idempotent

Retry Scenario

Implementation Strategies:

  • Idempotency keys (client-generated)
  • Natural keys (order ID, transaction ID)
  • Database constraints (unique indexes)
  • Distributed locks

Q6: Explain rate limiting strategies.

Answer:

Token Bucket

Characteristics:

  • Allows bursts (up to bucket size)
  • Smooth rate over time
  • Most flexible

Fixed Window

Problem: Burst at window boundary

Sliding Window

Advantages: More accurate, prevents boundary bursts

Q7: Explain circuit breaker pattern.

Answer:

State Transitions

Configuration:

  • Failure threshold: 5 failures
  • Timeout: 30 seconds
  • Success threshold: 2 successes to close

Benefits:

  • Prevent cascading failures
  • Fail fast
  • Give service time to recover
  • Improve user experience

Q8: Explain service mesh architecture.

Answer:

Architecture

Request Flow

Features:

  • Traffic Management: Load balancing, routing, retries
  • Security: mTLS, authentication, authorization
  • Observability: Metrics, logs, traces
  • Resilience: Circuit breakers, timeouts

Popular Service Meshes:

  • Istio
  • Linkerd
  • Consul Connect

Q9: Explain event sourcing and CQRS.

Answer:

Traditional vs Event Sourcing

Event Store

CQRS (Command Query Responsibility Segregation)

Benefits:

  • Complete audit trail
  • Time travel (replay to any point)
  • Separate read/write optimization
  • Event-driven architecture

Challenges:

  • Complexity
  • Eventual consistency
  • Event schema evolution

Q10: Explain distributed tracing.

Answer:

Trace Structure

Trace Timeline

Context Propagation

Benefits:

  • Identify bottlenecks
  • Understand dependencies
  • Debug distributed systems
  • Measure latency

Tools:

  • Jaeger
  • Zipkin
  • OpenTelemetry

Summary

Medium protocol and design topics:

  • HTTP/2: Multiplexing, header compression
  • gRPC: Binary protocol, streaming, Protocol Buffers
  • Consensus: Raft/Paxos for distributed agreement
  • Message Queues: Point-to-point and pub/sub patterns
  • Idempotency: Safe retries in distributed systems
  • Rate Limiting: Token bucket, sliding window
  • Circuit Breaker: Prevent cascading failures
  • Service Mesh: Traffic management, security, observability
  • Event Sourcing/CQRS: Event-driven architecture
  • Distributed Tracing: End-to-end request tracking

These concepts enable building robust distributed systems.

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