Prerequisite

Java 11 or later
SBT 1.3.6 or later
Docker 20.10.14 or higher (to run locally)

Introduction

If you have gone through the Explore Kalix Virtaully journey, you are all set to :

• Run locally in prod-like environment
  
• Deploy and run on Kalix Platform on Cloud Provider of your choice

However, if you would like to better understand the Kalix Developer Experience and how to build applications on Kalix, here is more detail on the same usecase.

Kalix Trial - eCommerce - Scala

Designing Kalix Services

Use case

eCommerce use case is a simple shopping cart example consisting of product stock and shopping cart. Product stock models stock (simple quantity) of products that are being sold and Shopping Cart models list of products customer intends to buy.
In this exercise the focus is on implementing Product Stock functionalities

Product Stock

Data model:

• quantity

Note: Product stock data model does not hold the productId because the HTTP/REST API is designed around productId itself. Operations:

• CREATE/READ/UPDATE/DELETE product stock

Kalix components

Kalix components serve to abstract functionalities.
In this particular use case, we will utilize a Kalix component known as Entity.

Entity:

• component for modeling of data and data business logic operations
• removes complexities around data:
  • caching
  • concurrency
  • distributed locking
• simplifies data modeling, business logic implementation with out-of-the box scalability, resilience Kalix provides other components that are not used in this use case and more details can be found in Kalix documentation:
  
  

Design Product Stock Kalix service

Product Stock Service

• implements Product Stock functionalities
• Kalix component used: Entity

ProductStock Entity

• models one product stock instance and business logic operations over that one instance

Data model

• quantity

API

• HTTP/RES
• Endpoints:

  • Create POST /product-stock/{productId}/create

    Request (JSON):

    • quantity (int)

    Response (JSON): {}

  • Read GET /product-stock/{productId}/get Request (JSON): No body

    Response (JSON):

    • quantity (int)

  • Update PUT /product-stock/{productId}/update

    Request (JSON):

    • quantity (int)

    Response (JSON): {}

  • Delete DELETE /product-stock/{productId}/delete

    Request (JSON): No body

    Response (JSON): {}

Kickstart Kalix development project

Kalix giter8 template

Kalix giter8 generates a new Scala development project from Kalix template

Create shopping cart Scala project from Kalix template

Execute in command line:

sbt new lightbend/kalix-value-entity.g8

Use this setup:

name [My Kalix Project]: kalix-trial-shoppingcart-scala
sbt_version [1.9.2]: <enter>
scala_version [2.13.10]: <enter>
package [com.example]: com.example.shoppingcart

giter8 generates Scala project:

• build.sbt with all pre-configured SBT plugins and dependencies required development, testing and packaging of Kalix service code
• src/main/protobuf directory with Kalix protobuf examples
• src/main/resources directory with minimal required configuration
• src/test/resources directory with minimal required configuration for test

Note: delete Kalix protobuf example files (counter_api.proto, domain/counter_domain.proto). Also delete domain directory.
Note: kalix_policy.proto is used to configure Kalix ACLs on service level. More information can be found in documenation.

Define data structure

1. Create package productstock in src/main/protobuf
2. Create protobuf file productstock_domain.proto in src/main/protobuf/productstock
3. Add ProductStock protobuf definition that represents ProductStock data structure that is persisted:

syntax = "proto3";
package com.example.shoppingcart.productstock;
message ProductStock{
    int32 quantity = 1;
}

Define API - Product Stock Entity API

1. Create protobuf file productstock_api.proto in src/main/protobuf/productstock
2. Add protobuf definitions represending Product Stock API requests:

syntax = "proto3";

import "google/protobuf/empty.proto";
import "kalix/annotations.proto";
import "google/api/annotations.proto";

import "com/example/shoppingcart/productstock/productstock_domain.proto";

package com.example.shoppingcart.productstock;

message CreateProductStockRequest {
  string product_id = 1 [(kalix.field).entity_key = true];
  int32 quantity = 2;
}

message UpdateProductStockRequest {
  string product_id = 1 [(kalix.field).entity_key = true];
  int32 quantity = 2;
}

message DeleteProductStockRequest {
  string product_id = 1 [(kalix.field).entity_key = true];
}

message GetProductStock {
  string product_id = 1 [(kalix.field).entity_key = true];
}

3. Add protobuf definition for a Product Stock GRPC service with corresponding rpc methods representing each endpoint

service ProductStockService {
  rpc Create(CreateProductStockRequest) returns (google.protobuf.Empty);
  rpc Get(GetProductStock) returns (ProductStock);
  rpc Update(UpdateProductStockRequest) returns (google.protobuf.Empty);
  rpc Delete(DeleteProductStockRequest) returns (google.protobuf.Empty);
  }

4. Exposing HTTP/REST endpoints from GRPC service using GRPC Transcoding HTTP/JSON to GRPC

service ProductStockService {
  rpc Create(CreateProductStockRequest) returns (google.protobuf.Empty){
    option (google.api.http) = {
      post: "/product-stock/{product_id}/create"
      body: "*"
    };
  }
  rpc Get(GetProductStock) returns (ProductStock){
    option (google.api.http) = {
      get: "/product-stock/{product_id}/get"
    };
  }
  rpc Update(UpdateProductStockRequest) returns (google.protobuf.Empty){
    option (google.api.http) = {
      put: "/product-stock/{product_id}/update"
      body: "*"
    };
  }
  rpc Delete(DeleteProductStockRequest) returns (google.protobuf.Empty){
    option (google.api.http) = {
      delete: "/product-stock/{product_id}/delete"
    };
  }
}

Implementing business logic

Code generation

1. Code generation from protobuf definitions Kalix SDK SBT plugin uses defined protobuf definitions to build required codebase (skeleton classes) where business logic can be developed in.
   Kalix SDK SBT plugin needs to be configured using custom kalix protobuf definition:

service ProductStockService {
  option (kalix.codegen) = {
    value_entity: {
      name: "com.example.shoppingcart.productstock.ProductStockEntity"
      entity_type: "product-stock"
      state: "com.example.shoppingcart.productstock.ProductStock"
    }
  };

• value_entity configures key-value as a durable storage model
• name configures the name of the Entity class that is being generated
• entity_type configures the entity type reference name that can be used to reference Entity in other Kalix components
• state configures the reference to ProductStock protobuf definition defined in productstock_domain.proto

2. Generate code using Kalix SBT plugin:

sbt compile

Generated code in src:

• src/main/scala
  • Main object for bootstraping Kalix service where all used Kalix components need to be registered
  • ProductStockEntity skeleton class where business logic needs to be developed in
• src/test/scala
  • ProductStockEntitySpec scalatest spec class for unit testing (covered in Test - Unit test section)
  • ProductStockServiceIntegrationSpec scalatest spec class for integration testing (covered in Test - Integration test section)

Note: Generated code in src will not be overwritten/regenerated in next in compile but only codebase in target.

ProductStockEntity business logic

For each Entity emptyState method, that returns an empty ProductStock needs to be implemented. We can use protobuf generated defaultInstance.

override def emptyState: ProductStock = ProductStock.defaultInstance

create endpoint

Business logic for create is to persist product stock data if not yet exists. In other cases returns an ERROR.

override def create(currentState: ProductStock, createProductStockRequest: CreateProductStockRequest): ValueEntity.Effect[Empty] = 
if (currentState == ProductStock.defaultInstance)
  effects.updateState(ProductStock.of(createProductStockRequest.quantity)).thenReply(Empty.defaultInstance)
else
  effects.error("Already created")

get endpoint

Business logic for get is to get product stock data if it exists and if not return not found error.

override def get(currentState: ProductStock, getProductStock: GetProductStock): ValueEntity.Effect[ProductStock] =
if (currentState == ProductStock.defaultInstance)
  effects.error("Not found", Status.Code.NOT_FOUND)
else
  effects.reply(currentState)

update endpoint

Business logic for update is to update product stock data if product was already created. If product is not found, return NOT FOUND error.

override def update(currentState: ProductStock, updateProductStockRequest: UpdateProductStockRequest): ValueEntity.Effect[Empty] =
if (currentState == ProductStock.defaultInstance)
  effects.error("Not found", Status.Code.NOT_FOUND)
else
  effects.updateState(currentState.withQuantity(updateProductStockRequest.quantity)).thenReply(Empty.defaultInstance)

delete endpoint

Business logic for delete is delete data if product stock exists and return NOT FOUND error if not. Here the soft delete is done by updating the state to ProductStock.defaultInstance.

override def delete(currentState: ProductStock, deleteProductStockRequest: DeleteProductStockRequest): ValueEntity.Effect[Empty] =
if (currentState == ProductStock.defaultInstance)
  effects.error("Not found", Status.Code.NOT_FOUND)
else
  effects.updateState(ProductStock.defaultInstance).thenReply(Empty.defaultInstance)

Test

Kalix comes with very rich test kit for unit and integration testing of Kalix code.

Test kit provides help (custom assertions, mocks,...) with:

• unit testing of individual Kalix components (e.g Entity) in isolation

• integration testing in Kalix Platform simulated environment in isolation

• Allows easy test automation with very high test coverage

Unit test

1. Edit test/scala/com/example/shoppingcart/productstock/ProductStockEntitySpec
2. Delete all tests instead of handle command Create
3. ProductStockEntityTestKit is a generated testKit class used for unit testing Value Entity component. It is for unit testing one product stock instance so productId needs to be provided. Call methods are generated based on the entity endpoints.

"handle command Create" in {
  val productId = UUID.randomUUID.toString
  val quantity = 10
  val testKit = ProductStockEntityTestKit(productId, new ProductStockEntity(_))
  val result = testKit.create(CreateProductStockRequest(productId = productId, quantity = quantity))
  result.isError shouldBe false
  result.reply shouldBe Empty.defaultInstance
  testKit.currentState().quantity shouldBe quantity
}

Run the unit test:

sbt test

Integration test

Kalix test kit for integration testing runs code using test containers to simulate Kalix Platform runtime environment. Integration test uses generated grpc client.

    "have example test that can be removed" in {
      val productId = UUID.randomUUID.toString
      val quantity = 10
      val createResult = client.create(CreateProductStockRequest(productId = productId,quantity = quantity))
      createResult.futureValue
      val getResult = client.get(GetProductStock(productId = productId))
      getResult.futureValue.quantity shouldBe quantity
    }

Run the integration test:

sbt test

Run locally in prod-like environment

1. Run the Kalix Proxy container:

docker-compose up

2. Run Kalix service locally:

sbt run

This command runs the Kalix service locally and exposes it on localhost:9000.

Test

Testing using CURL:

1. Create product:

curl -XPOST -d '{ 
  "quantity": 10
}' http://localhost:9000/product-stock/apple/create -H "Content-Type: application/json"

Result:

"{}"

2. Get product:

curl -XGET http://localhost:9000/product-stock/apple/get

Result:

{"quantity":10}

3. Update product:

curl -XPUT -d '{
"quantity": 20
}' http://localhost:9000/product-stock/apple/update -H "Content-Type: application/json"

Result:

"{}"

4. Delete product:

curl -XDELETE http://localhost:9000/product-stock/apple/delete

Result:

"{}"

Deploy and run on Kalix Platform on Cloud Provider of your choice

1. Install Kalix CLI https://docs.kalix.io/kalix/install-kalix.html

2. Kalix CLI

   1. Register (FREE)

   kalix auth signup
   

   Note: The above command will open a browser where registration information can be filled in
   2. Login

   kalix auth login
   

   Note: The above command will open a browser where authentication approval needs to be provided
   

   3. Check your organization name

   kalix organization list
   

   Execute the above command to view a list of organizations associated with your account. Find your organization name, likely the same as your username.

   4. Create a project

   kalix projects new kalix-trial-java-ecommerce --region=gcp-us-east1 --organization=your-organization-name
   

   For trial projects, provide gcp-us-east1 as the region. Replace your-organization-name with your actual organization name obtained from the previous step.
   

   5. Authenticate local docker for pushing docker image to Kalix Container Registry (KCR)

   kalix auth container-registry configure
   

   Note: The command will output Kalix Container Registry (KCR) path that will be used with docker push to KCR
   

3. Extract Kalix user username

   kalix auth current-login
   

   Note: The command will output Kalix user details and column USERNAME will be used with docker push to KCR
   

4. Build and push the project image Trigger project build and docker push to KCR:

sbt Docker/publish -Ddocker.registry=kcr.us-east-1.kalix.io -Ddocker.username=<myusername>/kalix-trial-scala-ecommerce -Dkalix.project=kalix-trial-scala-ecommerce

Note: Replace <myusername> with username extracted Kalix user username done in previous section.
Note: More details about KCR image name format can be found in offical documentation here.
Note: kalix-trial-scala-ecommerce is a project name 5. Deploy service in Kalix project:

kalix service deploy kcr.us-east-1.kalix.io/<username>/kalix-trial-scala-ecommerce/kalix-trial-shoppingcart-scala:latest 

Note: Replace <myusername> with username extracted Kalix user username done in previous section. 6. Check deployment:

kalix service list

Result:

kalix service list                                                                         
NAME                                         AGE    REPLICAS   STATUS        IMAGE TAG                     
kalix-trial-shoppingcart                     50s    0          Ready         1.0-SNAPSHOT                  

Note: When deploying service for the first time it can take up to 1 minute for internal provisioning

Proxy connection to Kalix service via Kalix CLI

1. Proxy connection to Kalix service via Kalix CLI

kalix service proxy kalix-trial-shoppingcart

Proxy Kalix CLI command will expose service proxy connection on localhost:8080.

Test

Testing using CURL:

1. Create product:

curl -XPOST -d '{ 
  "quantity": 10
}' http://localhost:8080/product-stock/apple/create -H "Content-Type: application/json"

Result:

"{}"

2. Get product:

curl -XGET http://localhost:8080/product-stock/apple/get

Result:

{"quantity":10}

3. Update product:

curl -XPUT -d '{
"quantity": 20
}' http://localhost:8080/product-stock/apple/update -H "Content-Type: application/json"

Result:

"{}"

4. Delete product:

curl -XDELETE http://localhost:8080/product-stock/apple/delete

Result:

"{}"