Resilience4j in Action

This repository contains examples for the Resilience4j library. The examples are written in Kotlin and use the Spring Boot Annotations of Resilience4J.

Scenario

Two services are involved in the scenario, the order-service and the transaction-log-service:

The order-service calls synchronously the transaction-log-service to log the created order and relies on its response. However, this call can fail.

Switch to the different pattern implementations

For each implemented resilience pattern there's a separate Git branch to be checked out. The following branches are available:

master: The initial state of the example, no resilience pattern is applied.
retry: Shows how the retry pattern might be applied.
rateLimiter: Shows how the rate limiter pattern might be applied.
circuitBreaker: Shows how the circuit breaker pattern might be applied.
fallback: Shows how the fallback pattern might be applied.

Run the example

Start the applications

The following command will start the order-service on port 8081:

cd order-service &&./gradlew bootRun --parallel

And the transaction-log-service on port 8082:

cd transaction-log-service &&./gradlew bootRun --parallel

Make the transaction-log-service fail

The transaction-log-service can be made to fail pseudo-randomly by setting the might-fail property in the application.yml to true:

transaction-log-service:
  feature-toggles:
    might-fail: true

Execute requests

The following curl command will do a POST request to the /ordersendpoint and pretty print the response's payload:

curl --request POST 'http://localhost:8081/orders' \
--header 'Content-Type: application/json' \
--data-raw '
{
  "userId": "aef251cb-ee9f-4317-8f86-1d3c907e4b5f",
  "items": [
    {
      "itemId": "b5106ea0-9d02-42f5-a7c0-93a71a0d02c1",
      "name": "Product A",
      "quantity": 2
    }
  ]
}
' | json_pp

If you need a repeating POST request, e.g. every half second, you could wrap it in a watch command:

watch -n 0.5 "curl --request POST 'http://localhost:8081/orders' \
--header 'Content-Type: application/json' \
--data-raw '
{
  \"userId\": \"aef251cb-ee9f-4317-8f86-1d3c907e4b5f\",
  \"items\": [
    {
      \"itemId\": \"b5106ea0-9d02-42f5-a7c0-93a71a0d02c1\",
      \"name\": \"Product A\",
      \"quantity\": 2
    }
  ]
}
' | json_pp"

(You might have to install curl and watch, e.g. on macOS with brew install curland brew install watch.)

Alternatively you could use ab of Apache Bench to do a tiny load test. There's already a post.json file provided in the project's root directory.

ab -T 'application/json' -n 20 -v 4 -p post.json http://localhost:8081/orders