Microservices with Kotlin and Ktor

Ktor is a Kotlin framework for creating web servers (and clients).
Unlike other frameworks, Ktor is written entirely in Kotlin and can therefore use language features such as Coroutines, reified Generics and Extension Functions more effectively.
With little overhead, fast results and good performance, Ktor is especially interesting for microservices.
If you are bored with Spring, you will find what you are looking for here. All others learn at least something new.

by Lovis
presented on May 2, 2019 @car2go

Transcript

1. Microservices with Lovis Möller @lovisbrot lovis.moeller@codecentric.de Kotlin and Ktor
2. Microservices — still a thing? https://www.amazon.de/Building-Microservices-Designing-Fine-Grained-Systems/dp/1492034029/
3. It depends.
4. Quickly adapt to changes of a fast-moving market.
5. Quickly adapt to changes of a fast-moving market. Works best with multiple small teams.
6. Quickly adapt to changes of a fast-moving market. Works best with multiple small teams. Not cheap.
7. Ok! Microservices it is. Let’s do it with Kotlin and Ktor.
8. • Consice, Safe, Pragmatic and tool-friendly • Created by JetBrains • Runs on the JVM, multi-platform and native. • 100% interoperable with Java • Open Source Kotlin
9. • Framework for Webservers (and -clients) • Written in Kotlin • Coroutines, Extension functions, internal DSLs • Open Source • https://ktor.io/quickstart/ Ktor
10. fun main() { embeddedServer(Netty, port = 8080) { routing { get("/") { call.respondText("Hello World!") } } }.start(wait = true) }
11. fun main() { embeddedServer(Netty, port = 8080) { routing { get("/") { call.respondText("Hello World!") } } }.start(wait = true) }
12. fun main() { embeddedServer(Netty, port = 8080) { routing { get("/") { call.respondText("Hello World!") } } }.start(wait = true) }
13. fun main() { embeddedServer(Netty, port = 8080) { routing { get("/") { call.respondText("Hello World!") } } }.start(wait = true) } Named Arguments
14. fun main() { embeddedServer(Netty, port = 8080) { routing { get("/") { call.respondText("Hello World!") } } }.start(wait = true) }
15. fun main() { embeddedServer(Netty, port = 8080) { routing { get("/") { call.respondText("Hello World!") } } }.start(wait = true) }
16. fun main() { embeddedServer( Netty, port = 8080, module = Application mainModule ).start(wait = true) }
17. fun main() { embeddedServer( Netty, port = 8080, module = Application module ).start(wait = true) }
18. fun Application.module() { routing { get("/") { call.respondText("Hello World!") } } }
19. fun Application.module() { routing { get("/") { call.respondText("Hello World!") } } } Extension Function
20. fun Application.module() { routing { get("/") { call.respondText("Hello World!") } } }
21. fun Application.module() { this.routing { get("/") { call.respondText("Hello World!") } } }
22. fun Application.module() { this.routing { get("/") { call.respondText("Hello World!") } } }
23. fun Application.module() { this.routing { get("/") { call.respondText("Hello World!") } } } this == Application
24. fun String.shuffle(): String { return this.toCharArray() .toList() .shuffled() .joinToString("") }
25. fun String.shuffle(): String { return this.toCharArray() .toList() .shuffled() .joinToString("") }
26. fun String.shuffle(): String { return this.toCharArray() .toList() .shuffled() .joinToString("") }
27. fun String.shuffle(): String { return this.toCharArray() .toList() .shuffled() .joinToString("") }
28. fun String.shuffle(): String { return this.toCharArray() .toList() .shuffled() .joinToString("") }
29. fun String.shuffle(): String { return this.toCharArray() .toList() .shuffled() .joinToString("") }
30. fun shuffle(): String { return this.toCharArray() .toList() .shuffled() .joinToString("") } Error!
31. fun String.shuffle(): String { return this.toCharArray() .toList() .shuffled() .joinToString("") }
32. fun String.shuffle(): String { return this.toCharArray() .toList() .shuffled() .joinToString("") }
33. fun String.shuffle(): String { return this.toCharArray() .toList() .shuffled() .joinToString("") }
34. fun String.shuffle(): String { return this.toCharArray() .toList() .shuffled() .joinToString("") }
35. fun String.shuffle(): String { return this.toCharArray() .toList() .shuffled() .joinToString("") } val shuffled = "techcamp".shuffle() println(shuffled)
36. fun String.shuffle(): String { return this.toCharArray() .toList() .shuffled() .joinToString("") } $ mactceph val shuffled = "techcamp".shuffle() println(shuffled)
37. Microservices Microservice ≈ Bounded Context Domain for this talk: Cat food configurator https://github.com/lmller/ktor-microservices-sample Sample code at
38. Cat food configurator Configure Food Add to cart Checkout Ingredient-warehouse maintenance Shipment Customer Self-Care
39. Cat food configurator Configure Food Add to cart Checkout Shipment Customer Warehouse employee Backoffice employee Ingredient-warehouse maintenance Customer Self-Care
40. Cat food configurator Configure Food Add to cart Checkout Shipment Customer Warehouse employee Backoffice employee Ingredient-warehouse maintenance Customer Self-Care Potential Users
41. Cat food configurator Configure Food Add to cart Checkout Shipment Ingredient-warehouse maintenance Customer Self-Care Potential Communication
42. Cat food configurator Configure Food Add to cart Checkout Shipment Ingredient-warehouse maintenance Customer Self-Care
44. fun Application.module() { val db = WarehouseDB() routing { get("/stock") { call.respond(db.stock.map {(name,quantity)  StockDto(name, quantity) }) } } } Warehouse
45. fun Application.module() { val db = WarehouseDB() routing { get("/stock") { call.respond(db.stock.map {(name,quantity)  StockDto(name, quantity) }) } } } Warehouse
46. fun Application.module() { val db = WarehouseDB() routing { get("/stock") { call.respond(db.stock.map {(name,quantity)  StockDto(name, quantity) }) } } } Warehouse
47. fun Application.module() { val db = WarehouseDB() routing { get("/stock") { call.respond(db.stock.map {(name,quantity)  StockDto(name, quantity) }) } } } Warehouse
48. fun Application.module() { val db = WarehouseDB() routing { get("/stock") { call.respond(db.stock.map {(name,quantity)  StockDto(name, quantity) }) } } } 500 InternalServerError Warehouse
49. fun Application.module() { val db = WarehouseDB() routing { get("/stock") { call.respond(db.stock.map {(name,quantity)  StockDto(name, quantity) }) } } } Warehouse
50. fun Application.module() {  routing { get("/stock") { call.respond(warehouse.stock.map { (k, v)  StockDto(k, v) }) }  Warehouse
51. fun Application.module() { install(ContentNegotiation) { jackson { enable(SerializationFeature.INDENT_OUTPUT) } }  routing { get("/stock") { call.respond(warehouse.stock.map { (k, v)  StockDto(k, v) }) }  Warehouse
52. fun Application.module() { install(ContentNegotiation) { jackson { enable(SerializationFeature.INDENT_OUTPUT) } }  routing { get("/stock") { call.respond(warehouse.stock.map { (k, v)  StockDto(k, v) }) }  Warehouse
53. fun Application.module() { install(ContentNegotiation) { jackson { enable(SerializationFeature.INDENT_OUTPUT) } }  routing { get("/stock") { call.respond(warehouse.stock.map { (k, v)  StockDto(k, v) }) }  [ { "name" : "Beef","quantity" : 100 }, { "name" : "Lamb","quantity" : 50 }, { "name" : "Fish","quantity" : 0 } ] Warehouse
54. get(" ") { }
55. get(" ") { } post(" ") { }
56. get(" ") { } post(" ") { } put(" ") { }
57. get(" ") { } post(" ") { } put(" ") { } patch(" ") { }
58. get(" ") { } post(" ") { } put(" ") { } patch(" ") { } delete(" ") { }
59. get(" ") { } post(" ") { } put(" ") { } patch(" ") { } delete(" ") { } head(" ") { }
60. get(" ") { } post(" ") { } put(" ") { } patch(" ") { } delete(" ") { } head(" ") { } options(" ") { }
61. get("/foo/bar") { } get("/foo/baz") { }
62. get("/foo/bar") { } get("/foo/baz") { } route("/foo") { get("/bar") { } get("/baz") { } }
63. get("/foo/bar") { } get("/foo/baz") { } route("/foo") { get("/bar") { } get("/baz") { } } https://ktor.io/servers/features/routing.html#routing-tree
64. fun Application.module() { install(ContentNegotiation) { … } val db = WarehouseDB() routing { get("/stock") { call.respond(db.stock.map {(name,quantity)  StockDto(name, quantity) }) } } } Warehouse
65. fun Application.module() { install(ContentNegotiation) { … } val db = WarehouseDB() routing { get("/stock") { call.respond(db.stock.map {(name,quantity)  StockDto(name, quantity) }) } } } Warehouse
66. private object StockTable : UUIDTable() { val itemName = varchar("itemName", 128).uniqueIndex() val quantity = integer("quantity") } Warehouse
67. private object StockTable : UUIDTable() { val itemName = varchar("itemName", 128).uniqueIndex() val quantity = integer("quantity") } Warehouse
68. private object StockTable : UUIDTable() { val itemName = varchar("itemName", 128).uniqueIndex() val quantity = integer("quantity") } Warehouse
69. private object StockTable : UUIDTable() { val itemName = varchar("itemName", 128).uniqueIndex() val quantity = integer("quantity") }  insert { column -> column[itemName] = "Fish" column[quantity] = 100 } Warehouse
70. private object StockTable : UUIDTable() { val itemName = varchar("itemName", 128).uniqueIndex() val quantity = integer("quantity") }  insert { column -> column[itemName] = "Fish" column[quantity] = 100 }  StockTable.selectAll() .map { it[StockTable.itemName] to it[StockTable.quantity] } .toMap() Warehouse
71. Warehouse private object StockTable : UUIDTable() { val itemName = varchar("itemName", 128).uniqueIndex() val quantity = integer("quantity") }  insert { column -> column[itemName] = "Fish" column[quantity] = 100 }  StockTable.selectAll() .map { it[StockTable.itemName] to it[StockTable.quantity] } .toMap() https://github.com/JetBrains/Exposed
72. fun Application.module() { install(ContentNegotiation) { … } routing { get("/stock") { … } put("/stock/{item}") { } } Warehouse
73. fun Application.module() { install(ContentNegotiation) { … } routing { get("/stock") { … } put("/stock/{item}") { val itemName = call.parameters.getOrFail("item") val stock = call.receive<StockDto>() db.update(itemName, stock.quantity ?: 0) call.respond(OK) } } Warehouse
74. fun Application.module() { install(ContentNegotiation) { … } routing { get("/stock") { … } put("/stock/{item}") { val itemName = call.parameters.getOrFail("item") val stock = call.receive<StockDto>() db.update(itemName, stock.quantity ?: 0) call.respond(OK) } } Warehouse
75. fun Application.module() { install(ContentNegotiation) { … } routing { get("/stock") { … } put("/stock/{item}") { val itemName = call.parameters.getOrFail("item") val stock = call.receive<StockDto>() db.update(itemName, stock.quantity ?: 0) call.respond(OK) } } Warehouse
76. fun Application.module() { install(ContentNegotiation) { … } routing { get("/stock") { … } put("/stock/{item}") { val itemName = call.parameters.getOrFail("item") val stock = call.receive<StockDto>() db.update(itemName, stock.quantity ?: 0) call.respond(OK) } } Warehouse
77. BASIC AUTH
78. fun Application.module() { install(ContentNegotiation) { … } install(Authentication) { } Warehouse
79. fun Application.module() { install(ContentNegotiation) { … } install(Authentication) { basic { validate { (user, pw)  if (user  "not-a-hacker" && pw  "supersecure!") UserIdPrincipal(user) else null } } } Warehouse
80. fun Application.module() { install(ContentNegotiation) { … } install(Authorization) { … } routing { get("/stock") { … } authenticate { put("/stock/{item}") { … } } } } Warehouse
82. fun Application.module() { install(FreeMarker) { templateLoader = ClassTemplateLoader( ) } Shop
83. fun Application.module() { install(FreeMarker) { templateLoader = ClassTemplateLoader( ) } routing { get("/") { val items = warehouseService.getStock() call.respond(FreeMarkerContent( "index.ftl", mapOf("items" to items) ) }
 } Shop
84. fun Application.module() { install(FreeMarker) { templateLoader = ClassTemplateLoader( ) } routing { get("/") { val items = warehouseService.getStock() call.respond(FreeMarkerContent( "index.ftl", mapOf("items" to items) ) }
 } Shop
85. <div> <h3>Items</h3> <ul> <#list items as item> <li>${item.name} - ${item.price}</li> </#list> </ul> </div> Shop
86. fun Application.module() { install(FreeMarker) { templateLoader = ClassTemplateLoader( ) } routing { get("/") { val items = warehouseService.getStock() call.respond(FreeMarkerContent( "index.ftl", mapOf("items" to items) ) }
 } Shop
87. Shop - Warehouse Api suspend fun getStock(): List<Item> { return httpClient.get<List<StockDto ("http://localhost:8080/stock") }
88. Shop - Warehouse Api suspend fun getStock(): List<Item> { return httpClient.get<List<StockDto ("http://localhost:8080/stock") }
89. suspend fun getStock(): List<Item> { return httpClient.get<List<StockDto ("http://localhost:8080/stock") } val httpClient = HttpClient(OkHttp) { install(JsonFeature) { serializer = JacksonSerializer() } } Shop - Warehouse Api
90. Shop - ShoppingCart & Orders Api suspend fun addToCart(item: Item) { httpClient.put<Unit>(shoppingCartUrl) { body = JsonContent(item) } }
91. suspend fun addToCart(item: Item) { httpClient.put<Unit>(shoppingCartUrl) { body = JsonContent(item) } } Shop - ShoppingCart & Orders Api
92. suspend fun addToCart(item: Item) { httpClient.put<Unit>(shoppingCartUrl) { body = JsonContent(item) } } private val shoppingCartUrl by lazy { application.environment.config .property("orders.shoppingcartUrl").getString() } Shop - ShoppingCart & Orders Api
94. Shopping Cart & Orders Service routing { put("/shoppingcart/items") { } }
95. routing { put("/shoppingcart/items") { val session = call.getSession() val itemToAdd = call.receive<Item>() call.sessions.set( session.copy(shoppingCart = session.shoppingCart + itemToAdd) ) call.respond(Created, "Added ${itemToAdd.name} to cart.") } } Shopping Cart & Orders Service
96. routing { put("/shoppingcart/items") { val session = call.sessions.get<UserSession>() val itemToAdd = call.receive<Item>() call.sessions.set( session.copy(shoppingCart = session.shoppingCart + itemToAdd) ) call.respond(Created, "Added ${itemToAdd.name} to cart.") } } Shopping Cart & Orders Service
97. routing { put("/shoppingcart/items") { val session = call.sessions.get<UserSession>() val itemToAdd = call.receive<Item>() call.sessions.set( session.copy(shoppingCart = session.shoppingCart + itemToAdd) ) call.respond(Created, "Added ${itemToAdd.name} to cart.") } } Shopping Cart & Orders Service
98. routing { put("/shoppingcart/items") { val session = call.sessions.get<UserSession>() val itemToAdd = call.receive<Item>() call.sessions.set( session.copy(shoppingCart = session.shoppingCart + itemToAdd) ) call.respond(Created, "Added ${itemToAdd.name} to cart.") } } ⚠ Sessions not RESTful Shopping Cart & Orders Service
99. install(Sessions) { cookie<UserSession>("CART", storage = SessionStorageMemory()) { cookie.path = "/" serializer = jacksonSessionSerializer() } } Shopping Cart & Orders Service
100. install(Sessions) { cookie<UserSession>("CART", storage = SessionStorageMemory()) { cookie.path = "/" serializer = jacksonSessionSerializer() } } data class UserSession(val name: String, val shoppingCart: List<Item>) Shopping Cart & Orders Service
101. install(Sessions) { cookie<UserSession>("CART", storage = SessionStorageMemory()) { cookie.path = "/" serializer = jacksonSessionSerializer() } } data class UserSession(val name: String, val shoppingCart: List<Item>) Shopping Cart & Orders Service
102. install(Sessions) { cookie<UserSession>("CART", storage = SessionStorageMemory()) { cookie.path = "/" serializer = jacksonSessionSerializer() } } data class UserSession(val name: String, val shoppingCart: List<Item>) toString() hashCode() equals() copy() Shopping Cart & Orders Service
103. Microservices with Ktor - a thing?
104. Ktor Not covered • Resilience • Monitoring & Metrics • Testing • Real Security
105. Ktor Not covered • Resilience • Monitoring & Metrics • Testing • Real Security • Under heavy development • Documentation needs improvement • Community is very helpful
106. Ktor Not covered • Resilience • Monitoring & Metrics • Testing • Real Security • Under heavy development • Documentation needs improvement • Community is very helpful https://ktor.io/quickstart/ http://slack.kotlinlang.org/ https://kotlinlang.org/
107. Lovis Möller @lovisbrot lovis.moeller@codecentric.de meetup.com/Kotlin-User-Group-Hamburg Images from https://unsplash.com/