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Marharyta Nedzelska

Software Engineer @ Wix.com

Building Microservices With Kotlin and gRPC

marharytan@wix.com twitter@jMargaritaN github.com/leveretka

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Who am I?

Building Microservices with Kotlin and gRPC

Marharyta Nedzelska

Software Engineer @ Wix
KKUG & Kotlin Night Kyiv organizer
Devoxx UA program committee
Speaker at meetups and conferences
https://medium.com/@margoqueen95
@jMargaritaN twitter

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One more thing you should know

Building Microservices with Kotlin and gRPC

I like boxing!

So think twice before asking tricky questions!

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AGENDA

Why gRPC?

Protobuf

Implement Service

Error Handling

Testing

More libs for Kotlin

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AGENDA

Why gRPC?

Protobuf

Implement Service

Error Handling

Testing

More libs for Kotlin

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Who writes microservices today, please, raise your hands?

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Microservices Rock!

Independent
Scalable
Mix tech stacks
Parallel development
etc...

Building Microservices with Kotlin and gRPC

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The biggest issue in changing a monolith into microservices lies in changing the communication pattern.

Btw, who said this?

Darth Vader

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The biggest issue in changing a monolith into microservices lies in changing the communication pattern.

Btw, who said this?

Darth Vader

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The biggest issue in changing a monolith into microservices lies in changing the communication pattern.

Btw, who said this?

Martin Fowler

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Who uses http 1.1 and REST today, please, raise your hands?

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Clients

Servers

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Why

gRPC?

01

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Why gRPC?

Use HTTP/2

Single TCP connection
Bidirectional streaming
Flow control

Supports multiple languages
Binary, uses protobuf

Building Microservices with Kotlin and gRPC

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1991

http 0.9

Http protocol evolution

Building Microservices with Kotlin and gRPC

1996

http 1.0

1997

http 1.1

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Http protocol evolution

Building Microservices with Kotlin and gRPC

No progress here

2000

1999

1998

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Http protocol evolution

Building Microservices with Kotlin and gRPC

And here

2003

2002

2001

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Http protocol evolution

Building Microservices with Kotlin and gRPC

And still no progress...

2006

2005

2004

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Http protocol evolution

Building Microservices with Kotlin and gRPC

Are they alive?

2009

2008

2007

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Http protocol evolution

Building Microservices with Kotlin and gRPC

I guess no...

2012

2011

2010

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Http protocol evolution

Building Microservices with Kotlin and gRPC

And suddenly!

2015

2014

2013

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Http protocol evolution

Building Microservices with Kotlin and gRPC

2015

http/2

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Why gRPC?

Use HTTP/2

Single TCP connection
Bidirectional streaming
Flow control

Supports multiple languages
Binary, uses protobuf

Building Microservices with Kotlin and gRPC

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Why gRPC?

Use HTTP/2

Single TCP connection
Bidirectional streaming
Flow control

Supports multiple languages
Binary, uses protobuf

Building Microservices with Kotlin and gRPC

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27

Why gRPC?

Use HTTP/2

Single TCP connection
Bidirectional streaming
Flow control

Supports multiple languages
Binary, uses protobuf

Building Microservices with Kotlin and gRPC

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Why gRPC?

Use HTTP/2

Single TCP connection
Bidirectional streaming
Flow control

Supports multiple languages
Binary, uses protobuf

Building Microservices with Kotlin and gRPC

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Why gRPC?

Use HTTP/2

Single TCP connection
Bidirectional streaming
Flow control

Supports multiple languages
Binary, uses protobuf

Building Microservices with Kotlin and gRPC

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+

ScalaPB

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?

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AGENDA

Why gRPC?

Protobuf

Implement Service

Error Handling

Testing

More libs for Kotlin

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Protocol

Buffers

02

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Protocol buffers are Google’s language-neutral, platform-neutral, extensible mechanism for serializing structured data — think XML, but smaller, faster, and simpler.

https://developers.google.com/protocol-buffers/

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Sample .proto file

Building Microservices with Kotlin and gRPC

syntax = "proto3";

package helloworld;

service Greeter {

rpc SayHello (HelloRequest) returns (HelloReply) {}

}

message HelloRequest {

string name = 1;

}

message HelloReply {

string message = 1;

}

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Protobuf summary

Type Safety

Building Microservices with Kotlin and gRPC

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Protobuf summary

Type Safety
No schema violations

Building Microservices with Kotlin and gRPC

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Protobuf summary

Type Safety
No schema violations
Fast serialization/deserialization

Building Microservices with Kotlin and gRPC

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Protobuf summary

Type Safety
No schema violations
Fast serialization/deserialization
Backward compatibility

Building Microservices with Kotlin and gRPC

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Protobuf summary

Type Safety
No schema violations
Fast serialization/deserialization
Backward compatibility
Human readability

Building Microservices with Kotlin and gRPC

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AGENDA

Why gRPC?

Protobuf

Implement Service

Interceptors

Flow Control

Error Handling

Testing

More libs for Kotlin

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Implement Service

03

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What does ‘gRPC’ stand for?

Riddle

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“gRPC” means gRPC Remote Procedure Call

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Building Microservices with Kotlin and gRPC

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Let’s help gRPC team and think of other possible meanings!

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Task for this session

Write voting chat application
Send funny ‘gRPC’ meanings
Vote for them
Tweet with #JFuture and #gRPC tags and like tweets
Greet winners at the end of our session!
Enjoy!

Building Microservices with Kotlin and gRPC

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Application is here !

http://104.197.77.39:8080

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Statistics stream

Messages stream

Building Microservices with Kotlin and gRPC

chat-service

stats-service

Join

When user joins chat...

Messages stream

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New gRPC meaning

Chat Message

Building Microservices with Kotlin and gRPC

chat-service

stats-service

Chat

When user chats...

Chat Message

Stats

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Update votes

Building Microservices with Kotlin and gRPC

vote-service

stats-service

Vote

When user votes...

New vote

Stats

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First iteration is done!

Single calls

Building Microservices with Kotlin and gRPC

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First iteration is done!

Single calls
Server streaming

Building Microservices with Kotlin and gRPC

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First iteration is done!

Single calls
Server streaming
Bidirectional streaming

Building Microservices with Kotlin and gRPC

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First iteration is done!

Single calls
Server streaming
Bidirectional streaming
Simple stub

Building Microservices with Kotlin and gRPC

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First iteration is done!

Single calls
Server streaming
Bidirectional streaming
Simple stub
Blocking stub

Building Microservices with Kotlin and gRPC

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First iteration is done!

Single calls
Server streaming
Bidirectional streaming
Simple stub
Blocking stub
Future stub

Building Microservices with Kotlin and gRPC

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AGENDA

Why gRPC?

Protobuf

Implement Service

Error Handling

Testing

More libs for Kotlin

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Error Handling

04

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All happy families are alike; each unhappy family is unhappy in its own way.

Btw, who said this?

Leo Tolstoy

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Success

OK

Building Microservices with Kotlin and gRPC

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Error

Building Microservices with Kotlin and gRPC

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Error

Building Microservices with Kotlin and gRPC

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Error

Building Microservices with Kotlin and gRPC

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What about custom exceptions?

Server returns Status.Unknown if threw an exception

Building Microservices with Kotlin and gRPC

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What about custom exceptions?

Server returns Status.Unknown if threw an exception
Return proper Status in Interceptor

Building Microservices with Kotlin and gRPC

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Server interceptor

Use close method to change returned status

override fun <ReqT, RespT> interceptCall(call: ServerCall<ReqT, RespT>,

headers: Metadata, next: ServerCallHandler<ReqT, RespT>) : ServerCall.Listener<ReqT> {

val wrappedCall = object : ForwardingServerCall.SimpleForwardingServerCall<ReqT, RespT>(call) {

override fun close(status: Status, trailers: Metadata) {

var status = status

if (status.code == Status.Code.UNKNOWN && status.description == null

&& status.cause != null && throwables.contains(status.cause!!.javaClass)) {

val t = status.cause

status = Status.INTERNAL.withDescription(t!!.message)

.augmentDescription(stacktraceToString(t))

}

super.close(status, trailers)

}

return next.startCall(wrappedCall, headers)

}

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Server interceptor

Use close method to change returned status

override fun <ReqT, RespT> interceptCall(call: ServerCall<ReqT, RespT>,

headers: Metadata, next: ServerCallHandler<ReqT, RespT>) : ServerCall.Listener<ReqT> {

val wrappedCall = object : ForwardingServerCall.SimpleForwardingServerCall<ReqT, RespT>(call) {

override fun close(status: Status, trailers: Metadata) {

var status = status

if (status.code == Status.Code.UNKNOWN && status.description == null

&& status.cause != null && throwables.contains(status.cause!!.javaClass)) {

val t = status.cause

status = Status.INTERNAL.withDescription(t!!.message)

.augmentDescription(stacktraceToString(t))

}

super.close(status, trailers)

}

return next.startCall(wrappedCall, headers)

}

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What about custom exceptions?

Server returns Status.Unknown if threw an exception
Return proper Status in Interceptor
Handle status codes in client

Building Microservices with Kotlin and gRPC

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Client

Catch Status Runtime Exception

try {

stub.doSth(request)

} catch (e: StatusRuntimeException) {

logger.log(Level.SEVERE, e.message, e)

}

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AGENDA

Why gRPC?

Protobuf

Implement Service

Error Handling

Testing

More libs for Kotlin

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Testing

05

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Unit testing

Use InProcessServerBuilder
Use InProcessChannelBuilder

Building Microservices with Kotlin and gRPC

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Let’s test chat method on server

lateinit var server: Server

lateinit var inProcessChannel: ManagedChannel

@Before

@Throws(Exception::class)

fun setUp() {

val serverName = InProcessServerBuilder.generateName()

server = InProcessServerBuilder.forName(serverName).directExecutor()

.addService(ManualFlowChatServiceImpl())

.build().start()

inProcessChannel = InProcessChannelBuilder.forName(serverName).directExecutor().build()

}

Building Microservices with Kotlin and gRPC

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Let’s test chat method on server

lateinit var server: Server

lateinit var inProcessChannel: ManagedChannel

@Before

@Throws(Exception::class)

fun setUp() {

val serverName = InProcessServerBuilder.generateName()

server = InProcessServerBuilder.forName(serverName).directExecutor()

.addService(ChatServiceImpl())

.build().start()

inProcessChannel = InProcessChannelBuilder.forName(serverName).directExecutor().build()

}

Building Microservices with Kotlin and gRPC

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Unit testing

Use InProcessServerBuilder
Use InProcessChannelBuilder
Do not forget to clean up

Building Microservices with Kotlin and gRPC

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Let’s test chat method on server

@RunWith(JUnit4::class)

class ChatServiceTest {

lateinit var server: Server

lateinit var inProcessChannel: ManagedChannel

...

@After

fun tearDown() {

inProcessChannel.shutdown()

server.shutdown()

}

...

}

Building Microservices with Kotlin and gRPC

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Unit testing

Use InProcessServerBuilder
Use InProcessChannelBuilder
Do not forget to clean up
Write tests

Building Microservices with Kotlin and gRPC

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Let’s test chat method on server

@Test

fun chatTest() {

val stub = ChatServiceGrpc.newStub(inProcessChannel)

val responseObserver: StreamObserver<ChatProto.ChatMessage> = mock { }

val requestObserver = stub.chat(responseObserver)

val chatMessage = ChatMessage.newBuilder().setFrom("Margo").setContent("Hello!").build()

val chatMessageCaptor: ArgumentCaptor<ChatProto.ChatMessage> =

ArgumentCaptor.forClass(ChatMessage::class.java)

requestObserver.onNext(chatMessage)

chatMessageCaptor.run {

verify(responseObserver).onNext(capture())

assertEquals("Margo", value.from)

assertEquals("Hello!", value.content)

}

Building Microservices with Kotlin and gRPC

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Let’s test chat method on server

@Test

fun chatTest() {

val stub = ChatServiceGrpc.newStub(inProcessChannel)

val responseObserver: StreamObserver<ChatProto.ChatMessage> = mock { }

val requestObserver = stub.chat(responseObserver)

val chatMessage = ChatMessage.newBuilder().setFrom("Margo").setContent("Hello!").build()

val chatMessageCaptor: ArgumentCaptor<ChatProto.ChatMessage> =

ArgumentCaptor.forClass(ChatMessage::class.java)

requestObserver.onNext(chatMessage)

chatMessageCaptor.run {

verify(responseObserver).onNext(capture())

assertEquals("Margo", value.from)

assertEquals("Hello!", value.content)

}

Building Microservices with Kotlin and gRPC

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What about integration

and e2e test?

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If you made a death star

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You should provide staff to test it!

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Testing summary

Write unit tests

Building Microservices with Kotlin and gRPC

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Testing summary

Write unit tests
Deal with streaming easily

Building Microservices with Kotlin and gRPC

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Testing summary

Write unit tests
Deal with streaming easily
No unified approach or lib for IT and e2e

Building Microservices with Kotlin and gRPC

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Testing summary

Write unit tests
Deal with streaming easily
No unified approach or lib for IT and e2e
At Wix testkits approach works for us

Building Microservices with Kotlin and gRPC

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AGENDA

Why gRPC?

Protobuf

Implement Service

Error Handling

Testing

More libs for Kotlin

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More libs for

Kotlin

06

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Building Microservices with Kotlin and gRPC

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Expectation

Building Microservices with Kotlin and gRPC

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Reality

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https://github.com/rouzwawi/grpc-kotlin.git

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https://github.com/rouzwawi/grpc-kotlin.git

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https://github.com/rouzwawi/grpc-kotlin.git

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https://github.com/marcoferrer/kroto-plus.git

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Examples

�//Kroto+ Overloaded�val response = serviceStub.myRpcMethod {� id = 100� name = "some name"� }

Building Microservices with Kotlin and gRPC

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Examples

suspend fun findStrongestAttack(): StandProto.Attack {� val standService = StandServiceGrpc.newStub(managedChannel)� val characterService = CharacterServiceGrpc.newStub(managedChannel)� val deferredStands = characterService.getAllCharactersStream()� .map { character ->� async { standService.getStandByCharacter(character) }� }.toList()� val strongestAttack = deferredStands� .flatMap { it.await().attacksList }� .maxBy { it.damage } � return strongestAttack ?: StandProto.Attack.getDefaultInstance()}

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Examples

suspend fun findStrongestAttack(): StandProto.Attack {� val standService = StandServiceGrpc.newStub(managedChannel)� val characterService = CharacterServiceGrpc.newStub(managedChannel)� val deferredStands = characterService.getAllCharactersStream()� .map { character ->� async { standService.getStandByCharacter(character) }� }.toList()� val strongestAttack = deferredStands� .flatMap { it.await().attacksList }� .maxBy { it.damage } � return strongestAttack ?: StandProto.Attack.getDefaultInstance()}

Building Microservices with Kotlin and gRPC

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Examples

val attack = Attack {� name = "ORA ORA ORA"� damage = 100� range = StandProto.Attack.Range.CLOSE}�//Copy extensions are also generated�val newAttack = attack.copy { damage = 200 } ��//As well as plus operator extensions �val mergedAttack = attack + Attack { name = "Sunlight Yellow Overdrive" }

Building Microservices with Kotlin and gRPC

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One day we’ll have proper kotlin support

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Takeaways

Use gRPC for effective communications
gRPC + Kotlin can be used today
Waiting for proper coroutines support
Feel free to contribute :)

INSERT YOUR�TOPIC NAME

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My gRPC Kotlin Sandbox

https://github.com/leveretka/grpc-chat.git

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Time to define winner!

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Thank You

marharytan@wix.com twitter@jMargaritaN github.com/leveretka

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Q&A

marharytan@wix.com twitter@jMargaritaN github.com/leveretka