go-cadence-example

Overview

go-cadence-example is a project for testing / demonstrating capabilities of candence, focusing on using it as a saga ochestrator. Cadence introduces concept of workflows: A fault-oblivious stateful function that orchestrates activities. A workflow has full control over which activities are executed, and in which order. Let's see how we could apply it for implementing orchestration-based saga pattern.

⚠️ This project is just playground. It contains lot of bad practices (including lack of interfaces, hard coded values etc.) which should not be followed. Maybe one day I will find some time to fix

Architecture

We are going to implement simple system consisting of services:

order - receving requests for a new bookings
payment - processing the payment oprations
orchestrator - defining, and controlling workflows execution

The execution chain will look as follow:

creating order -> processing payment -> marking order as created / failed

Order service will create an order in a INITATED state. Then, payment service validates the payment. if the payment value is greater than 100 the payment validation will fail. Based on the payment service response, order service is obligated to mark event as CREATED or FAILED.

The enum for order state look as follow:

UNDEFINED OrderStatus = 0
INITATED  OrderStatus = 1
CREATED   OrderStatus = 2
FAILED    OrderStatus = 3

Order service acts as a entry point to the system, exposing two REST endpoints:

POST /v1/order - creating the order
GET /v1/order/{id} - retreiving the order

⚠️ Order service for simplicity stores the orders in simple in memory mapping, so time it is restarted data is reseted.

In addition to these services we will need to start Cadence services:

cassandra
prometheus
node-exporter
cadence
cadence-web
grafana

Toolsets

We will use the golang for services implementation, utilising the go-kit library.

Setup

Requirements

docker-compose
docker

Setup

All services are created using docker-compose.

docker-compose up

It will start all services. Cadence services take some time to start so please be patient. Once all services are up and running we need to register (create) a domain for our application.

Cadence is backed by a multitenant service. The unit of isolation is called a domain. Each domain acts as a namespace for task list names as well as workflow IDs.

docker run --network=host --rm ubercadence/cli:master --domain samples-domain domain register

Now we can trigger our order creation:

curl --request POST \
  --url http://localhost:8082/v1/order \
  --header 'Content-Type: application/json' \
  --data '{
	"total_cost": 10,
	"vehicle_no": "123"
}'

To trigger the alternative flow, please change the input total_cost input filed to value > 100

And we check the order object using query:

curl --request GET \
  --url http://localhost:8082/v1/order/{id} \
  --header 'Content-Type: application/json'

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