This document discusses the technology behind LINE QR Code login. It describes the system architecture which uses a QR code login server, web browser for long polling session IDs, and Redis for publishing and subscribing to session channels. It also covers how Spring WebFlux is used, including its non-blocking request handling model and support for both reactive and traditional styles of coding.

1. Tech behind
LINE QR Code Login

2. Agenda 1. What is LINE Login?
2. Tech behind LINE QR Code Login
1. System Architecture
2. Spring WebFlux

3. Agenda 1. What is LINE Login?
2. Tech behind LINE QR Code Login
1. System Architecture
2. Spring WebFlux

4. • Social Login Service
• OAuth 2.0 / OpenID Connect 1.0
• Extended Features
• Messaging / Profile APIs
• Auto Login on smartphone web browser
• QR Code Login on PC web browser NEW!
• FIDO2 Support COMING SOON!
What is LINE Login?

5. What is QR Code Login?

6. Agenda 1. What is LINE Login?
2. Tech behind LINE QR Code Login
1. System Architecture
2. Spring WebFlux

7. backend
servers
System Architecture
REST/thrift
backend APIs
Login server
QR Code
Login server
gateway
server
web browser Redis Cluster
Session Storage
long polling
long polling
gateway
server
LINE
client app
QR Code Read Event
QR Code Read Event
Redis
PubSub

8. System Architecture
QR Code
Login server
web browser
long polling for sessionId
QR Code Read Event
including sessionId
Redis
PubSub
LINE
client app
via gateway server
via gateway/backend server
QR Code
Login server
publish to channel-{sessionId}
subscribe channel-{sessionId}
・・・・・
QR Code
including
sessionId

9. Agenda 1. What is LINE Login?
2. Tech behind LINE QR Code Login
1. System Architecture
2. Spring WebFlux

10. ● Each requests block and occupy a thread
up to 3 minutes
● Web framework based on event loop
concurrency model
● Each reqeusts do not block and do share the
thread
Spring WebFlux
request
request
request
request
request
request
Spring MVC (Servlet API)
Spring WebFlux

11. WebFlux with WebMVC
dependency spring-boot-
starter-web
○ ○ -
WebApplicationType (default) REACTIVE (default)
Filter ServletFilter WebFilter WebFilter
ThreadLocal OK ✗ ✗
@Controller Style OK OK OK
App Container Servlet
Reactive
via 'ServletAdapter'
Reactive
Reactive Style can block thread *1 OK *1 OK
MVC (blocking) Style block thread block thread block thread
*1 Flux stream operation runs on @Async threads

12. WebFlux with WebMVC
dependency spring-boot-
starter-web
○ ○ -
WebApplicationType (default) REACTIVE (default)
Filter ServletFilter WebFilter WebFilter
ThreadLocal OK ✗ ✗
@Controller Style OK OK OK
App Container Servlet
Reactive
via 'ServletAdapter'
Reactive
Reactive Style can block thread *1 OK *1 OK
MVC (blocking) Style block thread block thread block thread
*1 Flux stream operation runs on @Async threads
want to reuse
component

13. WebFlux with WebMVC
dependency spring-boot-
starter-web
○ ○ -
WebApplicationType (default) REACTIVE (default)
Filter ServletFilter WebFilter WebFilter
ThreadLocal OK ✗ ✗
@Controller Style OK OK OK
App Container Servlet
Reactive
via 'ServletAdapter'
Reactive
Reactive Style can block thread *1 OK *1 OK
MVC (blocking) Style block thread block thread block thread
*1 Flux stream operation runs on @Async threads
thread blocked

14. WebFlux with WebMVC
dependency spring-boot-
starter-web
○ ○ -
WebApplicationType (default) REACTIVE (default)
Filter ServletFilter WebFilter WebFilter
ThreadLocal OK ✗ ✗
@Controller Style OK OK OK
App Container Servlet
Reactive
via 'ServletAdapter'
Reactive
Reactive Style can block thread *1 OK *1 OK
MVC (blocking) Style block thread block thread block thread
*1 Flux stream operation runs on @Async threads
Hybrid container is expected....but ,actually,
both style code runs on same container and
same thread pool

15. WebFlux with WebMVC
dependency spring-boot-
starter-web
○ ○ -
WebApplicationType (default) REACTIVE (default)
Filter ServletFilter WebFilter WebFilter
ThreadLocal OK ✗ ✗
@Controller Style OK OK OK
App Container Servlet
Reactive
via 'ServletAdapter'
Reactive
Reactive Style can block thread *1 OK *1 OK
MVC (blocking) Style block thread block thread block thread
*1 Flux stream operation runs on @Async threads
cannot reuse
component

16. WebFlux with WebMVC
dependency spring-boot-
starter-web
○ ○ -
WebApplicationType (default) REACTIVE (default)
Filter ServletFilter WebFilter WebFilter
ThreadLocal OK ✗ ✗
@Controller Style OK OK OK
App Container Servlet
Reactive
via 'ServletAdapter'
Reactive
Reactive Style can block thread *1 OK *1 OK
MVC (blocking) Style block thread block thread block thread
*1 Flux stream operation runs on @Async threads
'Pure' WebFlux applied'Pure' WebFlux applied

17. WebFlux with WebMVC
dependency spring-boot-
starter-web
○ ○ -
WebApplicationType (default) REACTIVE (default)
Filter ServletFilter WebFilter WebFilter
ThreadLocal OK ✗ ✗
@Controller Style OK OK OK
App Container Servlet
Reactive
via 'ServletAdapter'
Reactive
Reactive Style can block thread *1 OK *1 OK
MVC (blocking) Style block thread block thread block thread
*1 Flux stream operation runs on @Async threads
need to rewrite ServletFilter
need ThreadLocal alternative

18. WebFilter
ServletFilter WebFilter
blocking OK NG
request HttpServerRequest ServerWebExchge.request
response HttpServerResponse ServerWebExchge.response
request attri
butes
HttpServerRequest.attributes[] ServerWebExchange.attributes[]
req/res cont
ent
HttpServletRequestWrapper Http
ServletResponseWrapper
ServerHttpRequestDecorator Ser
verHttpResponseDecorator
status code HttpServerResponse.status
ServerWebExchge.response
.statusCode
*1. null means 200OK

19. 2. Reactive style code is needed.
3. Some data cannot be retrieved in later stage.
WebFilter
← 3
← 2

20. A. Reactive style code is needed.
B. Request/response content is passed as Publisher<out DataBuffer>.
C. DataBuffer can be duplicated as java.nio.ByteBuffer.
WebFilter - ServerHttp*Decorator
← B
← A
← C
- HttpServlet*Wrapper alternative -

21. A. Take care of invocation order
Subscriber Context
- ThreadLocal alternative -
......
WebFilter UserLogic
1
2
3
4

22. B. Take care of propagate direction
Subscriber Context
- ThreadLocal alternative -
......
WebFilter UserLogic

23. B. Take care of propagate direction
Subscriber Context
- ThreadLocal alternative -
......
WebFilter UserLogic
Cannot read here

24. • PubSub
• Redis + Sentinel
• Log Aggregation
• kafka --> kafka-streams --> fluentd
• HBase + Hive + MySQL
• Web Application Server
• Kotlin
• Spring WebFlux + Reactor
• Lettuce
• Micrometer + Spring Actuator + Prometheus + Grafana
Other topics

25. THANK YOU