HTTP/2

HTTP/2 (RFC 7540, 2015) fixes the performance limitations of HTTP/1.1 with multiplexing, header compression, and server push.

HTTP/1.1 vs HTTP/2

HTTP/1.1 (Sequential):
Connection 1: [Request 1][Response 1][Request 2][Response 2]
Connection 2: [Request 3][Response 3][Request 4][Response 4]

HTTP/2 (Multiplexed):
Connection 1: [Req1][Req2][Req3][Req4]
              [Res1][Res2][Res3][Res4]  (interleaved)

Key HTTP/2 Features

Feature	Description	Benefit
Multiplexing	Multiple requests over one connection	Eliminates HOL blocking
Header Compression	HPACK compression for headers	Reduces overhead
Server Push	Server proactively sends resources	Faster page loads
Stream Priority	Prioritize important requests	Better UX

Multiplexing

HTTP/1.1:
  Connection 1: [===Request 1===]
  Connection 2: [===Request 2===]
  Connection 3: [===Request 3===]
  (6 connections max per domain)

HTTP/2:
  Single Connection:
  [Req1][Req2][Req3][Req4][Req5]
  [Res1][Res3][Res2][Res4][Res5]
  (all interleaved on one connection)

Header Compression (HPACK)

HTTP/1.1 Headers (uncompressed):
Host: api.example.com              (25 bytes)
Authorization: Bearer eyJhbG...    (50+ bytes)
Accept: application/json           (20 bytes)
Content-Type: application/json     (25 bytes)
                                  ─────────
Total: ~120 bytes (sent EVERY request)

HTTP/2 Headers (HPACK compressed):
First request: Full headers (~120 bytes)
Subsequent:    Only changed headers (~10-20 bytes)

Server Push

Client requests: GET /index.html

Without Push:
1. GET /index.html → Response
2. GET /style.css → Response
3. GET /app.js → Response
(Total: 3 round trips)

With Push:
1. GET /index.html
2. Server pushes: /style.css, /app.js
3. All arrive together
(Total: 1 round trip)

Enabling HTTP/2

Nginx:

server {
    listen 443 ssl http2;
    server_name api.example.com;
    # HTTP/2 automatically enabled with SSL
}

Spring Boot:

# application.properties
server.http2.enabled=true

HTTP/2 Priority

Streams can be prioritized:

Stream 1 (High Priority): /critical-api/data
Stream 2 (Low Priority):  /analytics/event
Stream 3 (Medium):        /user/profile

Server allocates bandwidth based on priority

When HTTP/2 Helps Most

Scenario	Improvement
Many small requests	Multiplexing eliminates connection overhead
Large headers	HPACK compression reduces size
Page with many resources	Server push reduces round trips
Mobile connections	Fewer connections = less battery drain