Resiliance4J

Resilience4j is a lightweight fault tolerance library designed for functional programming. Resilience4j provides higher-order functions (decorators) to enhance any functional interface, lambda expression or method reference with a Circuit Breaker, Rate Limiter, Retry or Bulkhead. You can stack more than one decorator on any functional interface, lambda expression or method reference. The advantage is that you have the choice to select the decorators you need and nothing else.

Resilience4j 2 requires Java 17.

Resiliance4J pattern

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In API Gateway, the burst limit represents the target maximum number of concurrent request submissions that API Gateway will fulfill

The burst limit defines the number of requests your API can handle concurrently. The rate limit defines the number of allowed requests per second. This is an implementation of the Token bucket implementation.

Let us assume below scenario

Service B is down or very slow to respond, in this case we can make use of resilance4j library

and implement below options

1. Retry

2. CircuitBreaker

3. Rate Limiter

4. BulkHead Circuit Breaker
   

code snippet- happy path

need to add resilance4j,aop,actuator dependency in pom.xml for serviceA,B

serviceB;

ServiceA:

Assume service A,B are working fine , in this case output would be

serviceB is called by ServiceA

Assume ServiceB is down, this is where it will cascade failure to service A , in such scenario, we will make use of ckt breaker pattern as below

serviceA:

enable management endpoit as below

application.yml

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enable cktbreaker

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we have defined 10 request in a given time, 50 % threshold- minmum 5 request to be failed, then cktbreaer fallback will kick in.

1. Retry

Rate Limiter

BulkHead