Server Push

Purpose

• Compare Server Push technologies
• Solve Load Balance questions in Server Push

Compare

Short Polling

• Easy
• HTTP basic, load balance compatibility good
• Make a lot of request, including lot of HTTP header (wasteful)
• No need to manage connections
• Simplex

Long Polling

• Easy
• HTTP basic, load balance compatibility good
• Make one request, but server will hold connection (less wasteful)
• Need to manage connections
• Simplex

Sse

• Normal
• HTTP basic, load balance compatibility good
• Server push (saving)
• Auto manage connections
• Simplex

WS

• Hard
• Handshake by HTTP, next ws tunnel, load balance compatibility bad
• Server push, without HTTP header (more saving)
• Need manage to connections
• Duplex
• It is the combination of low latency, high frequency and high volume that make the best case for the use WebSocket

Sse

Define

Server-sent Event

Procedure

• Generated SseEmitter
• Register SseEmitter Event
• Save SseEmitter for other programs
• Return SseEmitter in Controller

Ref

Sse Spring

WS

Define

WebSocket

Req & Res for begin

GET /spring-websocket-portfolio/portfolio HTTP/1.1
Host: localhost:8080
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Key: Uc9l9TMkWGbHFD2qnFHltg==
Sec-WebSocket-Protocol: v10.stomp, v11.stomp
Sec-WebSocket-Version: 13
Origin: http://localhost:8080

HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Accept: 1qVdfYHU9hPOl4JYYNXF623Gzn0=
Sec-WebSocket-Protocol: v10.stomp

Spring extensions

• @EnableWebSocket，启用 WebSocket
• WebSocketConfigurer，配置 WebSocket
• WebSocketHandler，处理 WebSocket 传输的信息
• HandshakeInterceptor，配置 WebSocket 连接建立之前、之后的处理
• ServletServerContainerFactoryBean，配置 WebSocket 信息大小等限制

STOMP

Procedure

• 建立 WS
• 建立 STOMP 客户端
• 客户端订阅服务端推送主题
• 客户端向服务端订阅的主题发布消息
• 服务端订阅客户端推送主题
• 服务端向客户端订阅的主题发布消息

Usage

• WebSocketMessageBrokerConfigurer，STOMP 配置
• @EnableWebSocketMessageBroker，启用 STOMP
• @MessageMapping，客户端发布消息，服务端订阅主题
• @SendTo，客户端订阅主题，服务端发布消息

Ref

Spring WebSocket doc

Server Push comparision

Spring WebSocket guide

Server Push Load Balance questions

Bug

前提：服务器A、服务器B、网页客户端A、手机客户端B

假设请求是扫码登录请求

• 进入用户登录页面，服务器 A 和网页客户端 A 建立 Server Push 连接（WS、SSE）
• 用户手机扫码，确认登录，发出登录请求，手机客户端 B 向服务器 B 发出登录请求
• 服务器 B 确认登录请求，由于 Server Push 连接是在服务器 A 上，服务器 B 无法推送消息到网页客户端 A

Solution

TDB