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Microservices with Lovis Möller @lovisbrot [email protected] Kotlin and Ktor

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Microservices — still a thing? https://www.amazon.de/Building-Microservices-Designing-Fine-Grained-Systems/dp/1492034029/

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It depends.

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Quickly adapt to changes of a fast-moving market.

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Quickly adapt to changes of a fast-moving market. Works best with multiple small teams.

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Quickly adapt to changes of a fast-moving market. Works best with multiple small teams. Not cheap.

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Ok! Microservices it is. Let’s do it with Kotlin and Ktor.

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• Consice, Safe, Pragmatic and tool-friendly • Created by JetBrains • Runs on the JVM, multi-platform and native. • 100% interoperable with Java • Open Source Kotlin

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• Framework for Webservers (and -clients) • Written in Kotlin • Coroutines, Extension functions, internal DSLs • Open Source • https://ktor.io/quickstart/ Ktor

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fun main() { embeddedServer(Netty, port = 8080) { routing { get("/") { call.respondText("Hello World!") } } }.start(wait = true) }

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fun main() { embeddedServer(Netty, port = 8080) { routing { get("/") { call.respondText("Hello World!") } } }.start(wait = true) }

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fun main() { embeddedServer(Netty, port = 8080) { routing { get("/") { call.respondText("Hello World!") } } }.start(wait = true) }

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fun main() { embeddedServer(Netty, port = 8080) { routing { get("/") { call.respondText("Hello World!") } } }.start(wait = true) } Named Arguments

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fun main() { embeddedServer(Netty, port = 8080) { routing { get("/") { call.respondText("Hello World!") } } }.start(wait = true) }

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fun main() { embeddedServer(Netty, port = 8080) { routing { get("/") { call.respondText("Hello World!") } } }.start(wait = true) }

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fun main() { embeddedServer( Netty, port = 8080, module = Application mainModule ).start(wait = true) }

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fun main() { embeddedServer( Netty, port = 8080, module = Application module ).start(wait = true) }

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fun Application.module() { routing { get("/") { call.respondText("Hello World!") } } }

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fun Application.module() { routing { get("/") { call.respondText("Hello World!") } } } Extension Function

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fun Application.module() { routing { get("/") { call.respondText("Hello World!") } } }

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fun Application.module() { this.routing { get("/") { call.respondText("Hello World!") } } }

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fun Application.module() { this.routing { get("/") { call.respondText("Hello World!") } } }

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fun Application.module() { this.routing { get("/") { call.respondText("Hello World!") } } } this == Application

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fun String.shuffle(): String { return this.toCharArray() .toList() .shuffled() .joinToString("") }

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fun String.shuffle(): String { return this.toCharArray() .toList() .shuffled() .joinToString("") }

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fun String.shuffle(): String { return this.toCharArray() .toList() .shuffled() .joinToString("") }

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fun String.shuffle(): String { return this.toCharArray() .toList() .shuffled() .joinToString("") }

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fun String.shuffle(): String { return this.toCharArray() .toList() .shuffled() .joinToString("") }

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fun String.shuffle(): String { return this.toCharArray() .toList() .shuffled() .joinToString("") }

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fun shuffle(): String { return this.toCharArray() .toList() .shuffled() .joinToString("") } Error!

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fun String.shuffle(): String { return this.toCharArray() .toList() .shuffled() .joinToString("") }

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fun String.shuffle(): String { return this.toCharArray() .toList() .shuffled() .joinToString("") }

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fun String.shuffle(): String { return this.toCharArray() .toList() .shuffled() .joinToString("") }

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fun String.shuffle(): String { return this.toCharArray() .toList() .shuffled() .joinToString("") }

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fun String.shuffle(): String { return this.toCharArray() .toList() .shuffled() .joinToString("") } val shuffled = "techcamp".shuffle() println(shuffled)

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fun String.shuffle(): String { return this.toCharArray() .toList() .shuffled() .joinToString("") } $ mactceph val shuffled = "techcamp".shuffle() println(shuffled)

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Microservices Microservice ≈ Bounded Context Domain for this talk: Cat food configurator https://github.com/lmller/ktor-microservices-sample Sample code at

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Cat food configurator Configure Food Add to cart Checkout Ingredient-warehouse maintenance Shipment Customer Self-Care

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Cat food configurator Configure Food Add to cart Checkout Shipment Customer Warehouse employee Backoffice employee Ingredient-warehouse maintenance Customer Self-Care

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Cat food configurator Configure Food Add to cart Checkout Shipment Customer Warehouse employee Backoffice employee Ingredient-warehouse maintenance Customer Self-Care Potential Users

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Cat food configurator Configure Food Add to cart Checkout Shipment Ingredient-warehouse maintenance Customer Self-Care Potential Communication

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Cat food configurator Configure Food Add to cart Checkout Shipment Ingredient-warehouse maintenance Customer Self-Care

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fun Application.module() { val db = WarehouseDB() routing { get("/stock") { call.respond(db.stock.map {(name,quantity)  StockDto(name, quantity) }) } } } Warehouse

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fun Application.module() { val db = WarehouseDB() routing { get("/stock") { call.respond(db.stock.map {(name,quantity)  StockDto(name, quantity) }) } } } Warehouse

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fun Application.module() { val db = WarehouseDB() routing { get("/stock") { call.respond(db.stock.map {(name,quantity)  StockDto(name, quantity) }) } } } Warehouse

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fun Application.module() { val db = WarehouseDB() routing { get("/stock") { call.respond(db.stock.map {(name,quantity)  StockDto(name, quantity) }) } } } Warehouse

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fun Application.module() { val db = WarehouseDB() routing { get("/stock") { call.respond(db.stock.map {(name,quantity)  StockDto(name, quantity) }) } } } 500 InternalServerError Warehouse

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fun Application.module() { val db = WarehouseDB() routing { get("/stock") { call.respond(db.stock.map {(name,quantity)  StockDto(name, quantity) }) } } } Warehouse

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fun Application.module() {  routing { get("/stock") { call.respond(warehouse.stock.map { (k, v)  StockDto(k, v) }) }  Warehouse

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fun Application.module() { install(ContentNegotiation) { jackson { enable(SerializationFeature.INDENT_OUTPUT) } }  routing { get("/stock") { call.respond(warehouse.stock.map { (k, v)  StockDto(k, v) }) }  Warehouse

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fun Application.module() { install(ContentNegotiation) { jackson { enable(SerializationFeature.INDENT_OUTPUT) } }  routing { get("/stock") { call.respond(warehouse.stock.map { (k, v)  StockDto(k, v) }) }  Warehouse

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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

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get(" ") { }

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get(" ") { } post(" ") { }

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get(" ") { } post(" ") { } put(" ") { }

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get(" ") { } post(" ") { } put(" ") { } patch(" ") { }

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get(" ") { } post(" ") { } put(" ") { } patch(" ") { } delete(" ") { }

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get(" ") { } post(" ") { } put(" ") { } patch(" ") { } delete(" ") { } head(" ") { }

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get(" ") { } post(" ") { } put(" ") { } patch(" ") { } delete(" ") { } head(" ") { } options(" ") { }

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get("/foo/bar") { } get("/foo/baz") { }

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get("/foo/bar") { } get("/foo/baz") { } route("/foo") { get("/bar") { } get("/baz") { } }

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get("/foo/bar") { } get("/foo/baz") { } route("/foo") { get("/bar") { } get("/baz") { } } https://ktor.io/servers/features/routing.html#routing-tree

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fun Application.module() { install(ContentNegotiation) { … } val db = WarehouseDB() routing { get("/stock") { call.respond(db.stock.map {(name,quantity)  StockDto(name, quantity) }) } } } Warehouse

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fun Application.module() { install(ContentNegotiation) { … } val db = WarehouseDB() routing { get("/stock") { call.respond(db.stock.map {(name,quantity)  StockDto(name, quantity) }) } } } Warehouse

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private object StockTable : UUIDTable() { val itemName = varchar("itemName", 128).uniqueIndex() val quantity = integer("quantity") } Warehouse

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private object StockTable : UUIDTable() { val itemName = varchar("itemName", 128).uniqueIndex() val quantity = integer("quantity") } Warehouse

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private object StockTable : UUIDTable() { val itemName = varchar("itemName", 128).uniqueIndex() val quantity = integer("quantity") } Warehouse

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private object StockTable : UUIDTable() { val itemName = varchar("itemName", 128).uniqueIndex() val quantity = integer("quantity") }  insert { column -> column[itemName] = "Fish" column[quantity] = 100 } Warehouse

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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

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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

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fun Application.module() { install(ContentNegotiation) { … } routing { get("/stock") { … } put("/stock/{item}") { } } Warehouse

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fun Application.module() { install(ContentNegotiation) { … } routing { get("/stock") { … } put("/stock/{item}") { val itemName = call.parameters.getOrFail("item") val stock = call.receive() db.update(itemName, stock.quantity ?: 0) call.respond(OK) } } Warehouse

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fun Application.module() { install(ContentNegotiation) { … } routing { get("/stock") { … } put("/stock/{item}") { val itemName = call.parameters.getOrFail("item") val stock = call.receive() db.update(itemName, stock.quantity ?: 0) call.respond(OK) } } Warehouse

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fun Application.module() { install(ContentNegotiation) { … } routing { get("/stock") { … } put("/stock/{item}") { val itemName = call.parameters.getOrFail("item") val stock = call.receive() db.update(itemName, stock.quantity ?: 0) call.respond(OK) } } Warehouse

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fun Application.module() { install(ContentNegotiation) { … } routing { get("/stock") { … } put("/stock/{item}") { val itemName = call.parameters.getOrFail("item") val stock = call.receive() db.update(itemName, stock.quantity ?: 0) call.respond(OK) } } Warehouse

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BASIC AUTH

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fun Application.module() { install(ContentNegotiation) { … } install(Authentication) { } Warehouse

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fun Application.module() { install(ContentNegotiation) { … } install(Authentication) { basic { validate { (user, pw)  if (user  "not-a-hacker" && pw  "supersecure!") UserIdPrincipal(user) else null } } } Warehouse

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fun Application.module() { install(ContentNegotiation) { … } install(Authorization) { … } routing { get("/stock") { … } authenticate { put("/stock/{item}") { … } } } } Warehouse

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fun Application.module() { install(FreeMarker) { templateLoader = ClassTemplateLoader( ) } Shop

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fun Application.module() { install(FreeMarker) { templateLoader = ClassTemplateLoader( ) } routing { get("/") { val items = warehouseService.getStock() call.respond(FreeMarkerContent( "index.ftl", mapOf("items" to items) ) }
 } Shop

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fun Application.module() { install(FreeMarker) { templateLoader = ClassTemplateLoader( ) } routing { get("/") { val items = warehouseService.getStock() call.respond(FreeMarkerContent( "index.ftl", mapOf("items" to items) ) }
 } Shop

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Items

    <#list items as item>
  • ${item.name} - ${item.price}
Shop

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fun Application.module() { install(FreeMarker) { templateLoader = ClassTemplateLoader( ) } routing { get("/") { val items = warehouseService.getStock() call.respond(FreeMarkerContent( "index.ftl", mapOf("items" to items) ) }
 } Shop

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Shop - Warehouse Api suspend fun getStock(): List { return httpClient.get

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Shop - Warehouse Api suspend fun getStock(): List { return httpClient.get

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suspend fun getStock(): List { return httpClient.get

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Shop - ShoppingCart & Orders Api suspend fun addToCart(item: Item) { httpClient.put(shoppingCartUrl) { body = JsonContent(item) } }

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suspend fun addToCart(item: Item) { httpClient.put(shoppingCartUrl) { body = JsonContent(item) } } Shop - ShoppingCart & Orders Api

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suspend fun addToCart(item: Item) { httpClient.put(shoppingCartUrl) { body = JsonContent(item) } } private val shoppingCartUrl by lazy { application.environment.config .property("orders.shoppingcartUrl").getString() } Shop - ShoppingCart & Orders Api

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Shopping Cart & Orders Service routing { put("/shoppingcart/items") { } }

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routing { put("/shoppingcart/items") { val session = call.getSession() val itemToAdd = call.receive() call.sessions.set( session.copy(shoppingCart = session.shoppingCart + itemToAdd) ) call.respond(Created, "Added ${itemToAdd.name} to cart.") } } Shopping Cart & Orders Service

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routing { put("/shoppingcart/items") { val session = call.sessions.get() val itemToAdd = call.receive() call.sessions.set( session.copy(shoppingCart = session.shoppingCart + itemToAdd) ) call.respond(Created, "Added ${itemToAdd.name} to cart.") } } Shopping Cart & Orders Service

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routing { put("/shoppingcart/items") { val session = call.sessions.get() val itemToAdd = call.receive() call.sessions.set( session.copy(shoppingCart = session.shoppingCart + itemToAdd) ) call.respond(Created, "Added ${itemToAdd.name} to cart.") } } Shopping Cart & Orders Service

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routing { put("/shoppingcart/items") { val session = call.sessions.get() val itemToAdd = call.receive() call.sessions.set( session.copy(shoppingCart = session.shoppingCart + itemToAdd) ) call.respond(Created, "Added ${itemToAdd.name} to cart.") } } ⚠ Sessions not RESTful Shopping Cart & Orders Service

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install(Sessions) { cookie("CART", storage = SessionStorageMemory()) { cookie.path = "/" serializer = jacksonSessionSerializer() } } Shopping Cart & Orders Service

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install(Sessions) { cookie("CART", storage = SessionStorageMemory()) { cookie.path = "/" serializer = jacksonSessionSerializer() } } data class UserSession(val name: String, val shoppingCart: List) Shopping Cart & Orders Service

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install(Sessions) { cookie("CART", storage = SessionStorageMemory()) { cookie.path = "/" serializer = jacksonSessionSerializer() } } data class UserSession(val name: String, val shoppingCart: List) Shopping Cart & Orders Service

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install(Sessions) { cookie("CART", storage = SessionStorageMemory()) { cookie.path = "/" serializer = jacksonSessionSerializer() } } data class UserSession(val name: String, val shoppingCart: List) toString() hashCode() equals() copy() Shopping Cart & Orders Service

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Microservices with Ktor - a thing?

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Ktor Not covered • Resilience • Monitoring & Metrics • Testing • Real Security

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Ktor Not covered • Resilience • Monitoring & Metrics • Testing • Real Security • Under heavy development • Documentation needs improvement • Community is very helpful

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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/

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Lovis Möller @lovisbrot [email protected] meetup.com/Kotlin-User-Group-Hamburg Images from https://unsplash.com/