Lari Hotari @lhotariPivotal Software, Inc.

Ratpack and Grails 3

Agenda

• Grails 3 and Ratpack

• Why async?

• Modularity and micro service architectures

• Embrace Gradle

• Abstract packaging / deployment

• Reach outside the servlet container

• App profiles: Netty, Servlet, Batch, Hadoop

• Lightweight deployments, support micro services

Grails 3

Why Netty / Ratpack? Why async?

Amdahl's law

Programming model• Declarative programming expresses the logic of

a computation without describing its control flow.

• It's programming without the call stack, the programmer doesn't decide execution details.

• Examples: functional and reactive programming, event / message based execution, distributed parallel computation algorithms like Map/Reduce

14 import ratpack.remote.RemoteControlModule 15 import ratpack.rx.RxRatpack 16 import ratpack.session.SessionModule 17 import ratpack.session.store.MapSessionsModule 18 import ratpack.session.store.SessionStorage 19 20 import static ratpack.groovy.Groovy.groovyTemplate 21 import static ratpack.groovy.Groovy.ratpack 22 import static ratpack.jackson.Jackson.json 23 import static ratpack.pac4j.internal.SessionConstants.USER_PROFILE 24 25 ratpack { 26 bindings { 27 bind DatabaseHealthCheck 28 add new CodaHaleMetricsModule().jvmMetrics().jmx().websocket(). 29 healthChecks() 30 add new HikariModule([URL: "jdbc:h2:mem:dev;INIT=CREATE SCHEMA IF NOT 31 EXISTS DEV"], "org.h2.jdbcx.JdbcDataSource") 32 add new SqlModule() 33 add new JacksonModule() 34 add new BookModule() 35 add new RemoteControlModule() 36 add new SessionModule() 37 add new MapSessionsModule(10, 5) 38 add new Pac4jModule<>(new FormClient("/login", new 39 SimpleTestUsernamePasswordAuthenticator()), new 40 AuthPathAuthorizer()) 41 42 init { BookService bookService -> 43 RxRatpack.initialize() 44 HystrixRatpack.initialize() 45 bookService.createTable() 46 } 47 } 48 49 handlers { BookService bookService -> 50 51 get { 52 bookService.all().toList().subscribe { List<Book> books -> 53 SessionStorage sessionStorage = request.get(SessionStorage) 54 UserProfile profile = sessionStorage.get(USER_PROFILE) 55 def username = profile?.getAttribute("username") 56 57 render groovyTemplate("listing.html", 58 username: username ?: "", 59 title: "Books", 60 books: books, 61 msg: request.queryParams.msg ?: "") 62 } 63 } 64 65 handler("create") { 66 byMethod { 67 get { 68 render groovyTemplate("create.html", title: "Create Book") 69 } 70 post { 71 Form form = parse(Form) 72 bookService.insert( 73 form.isbn, 74 form.get("quantity").asType(Long), 75 form.get("price").asType(BigDecimal) 76 ).single().subscribe { String isbn -> 77 redirect "/?msg=Book+$isbn+created" 78 } 79 } 80 } 81 } 82 83 handler("update/:isbn") { 84 def isbn = pathTokens["isbn"] 85 86 bookService.find(isbn).single().subscribe { Book book -> 87 if (book == null) { 88 clientError(404) 89 } else { 90 byMethod { 91 get { 92 render groovyTemplate("update.html", title: 93 "Update Book", book: book) 94 } 95 post { 96 Form form = parse(Form) 97 bookService.update( 98 isbn, 99 form.get("quantity").asType(Long), 100 form.get("price").asType(BigDecimal) 101 ) subscribe { 102 redirect "/?msg=Book+$isbn+updated" 103 } 104 } 105 } 106 } 107 } 108 } 109 110 post("delete/:isbn") { 111 def isbn = pathTokens["isbn"] 112 bookService.delete(isbn).subscribe { 113 redirect "/?msg=Book+$isbn+deleted" 114 } 115 } 116 117 prefix("api") { 118 get("books") { 119 bookService.all().toList().subscribe { List<Book> books -> 120 render json(books) 121 } 122 } 123 124 handler("book/:isbn?", registry.get(BookRestEndpoint)) 125 }

80 } 81 } 82 83 handler("update/:isbn") { 84 def isbn = pathTokens["isbn"] 85 86 bookService.find(isbn).single().subscribe { Book book -> 87 if (book == null) { 88 clientError(404) 89 } else { 90 byMethod { 91 get { 92 render groovyTemplate("update.html", title: 93 "Update Book", book: book) 94 } 95 post { 96 Form form = parse(Form) 97 bookService.update( 98 isbn, 99 form.get("quantity").asType(Long), 100 form.get("price").asType(BigDecimal) 101 ) subscribe { 102 redirect "/?msg=Book+$isbn+updated" 103 } 104 } 105 } 106 } 107 } 108 } 109 110 post("delete/:isbn") { 111 def isbn = pathTokens["isbn"] 112 bookService.delete(isbn).subscribe { 113 redirect "/?msg=Book+$isbn+deleted" 114 }

source: https://github.com/ratpack/example-books/blob/master/src/ratpack/Ratpack.groovy

Ratpack application consists of

functional handler chains

Ratpack applications• Ratpacks comes with Guice for dependency injection

• Guice modules are also used as the plugin system for Ratpack

• Examples of Ratpack module contributions:

• Integrations to RxJava and Reactor. Can be used for async composition and preventing "callback hell".

• Integration to Netflix Hystrix for adding error resilience functionality . f.e., Circuit-breaker pattern impl.

Demo Ratpack and Grails (GORM) used together

• https://github.com/lhotari/ratpack-gorm-example

• Spring Boot embedded in Ratpack, running GORM

Modularity

• logical partitioning of the "software design"

• allows complex software to be manageable for the purpose of implementation and maintenance

Coupling and Cohesion• Coupling and cohesion are measures for

describing how easy it will be to change the behaviour of some element in a system

• Modules are coupled if a change in one forces a change in a the other

• A module's cohesion is a measure of whether it's responsibilities form a meaningful unit

source: GOOS book

• Low coupling between modules ⟹ easier to change

• High cohesion within module ⟹ single responsibility

Microservice definition by James Lewis

• Each application only does one thing

• Small enough to fit in your head

• Small enough that you can throw them away

• Embedded web container

• Packaged as a single executable jar

• Use HTTP and HATEOAS to decouple services

• Each app exposes metrics about itself

–Arnon Rotem-Gal-Oz, Practical SOA

“Nanoservice is an Anti-pattern where a service is too fine grained. Nanoservice is a service whose overhead (communications,

maintenance etc.) out-weights its utility.”

Polygot persistence• Common principle is that each service owns it's data -

there is no shared database across multiple services.

• If this principle is followed, it usually means switching to Hexagonal architecture, where persistence is an integration and not part of the core.

• "Start with the events and behaviour instead of the database."

• Data consistency models in distributed systems

Brooks: "No silver bullet"

• Essential complexity

• complexity that you cannot escape

• Accidental complexity

• we could be adding complexity by bad design

- Google's "Solve for X"

“You don't spend your time being bothered that you can't teleport from here to Japan,

because there's a part of you that thinks it's impossible. !

Moonshot thinking is choosing to be bothered by that.”

Modular monoliths• Modular monoliths are composed of loosely coupled

modules of single responsibility

• Enabling the 3rd way (after monoliths and microservices) for building applications on the JVM across different libraries and frameworks

• Modules can be turned into true micro services when needed - instead of introducing accidental complexity to projects that don't really require micro services in the beginning, but could benefit of them later

The monoliths in the micro services architecture

Single Page App in

Browser

API Gateway service

µservice A

SAAS Service A

SAAS Service B

µservice B

µservice C

µservice D

µservice E

µservice F

"If you built it..."

 pretotyping.org

“Make sure you are building the right it before you build it right."

!

"Fail fast ... and Often"

Lari Hotari @lhotariPivotal Software, Inc.

Thank you!