Reference:

Resilience4j (Circuit Breaker)

Introduction

• Stops calling a failing service repeatedly.
• If service fails too much → stop calling it temporarily.
• Logic:
  • CLOSED → normal
  • OPEN → block calls
  • HALF-OPEN → test if recovered
• Setup fallback

let failures = 0;
let state = "CLOSED";

async function callService() {
  if (state === "OPEN") {
    throw new Error("Service unavailable");
  }

  try {
    const result = await fetch("<https://api.example.com>");
    failures = 0;
    return result;
  } catch (err) {
    failures++;
    if (failures >= 3) {
      state = "OPEN";
      setTimeout(() => state = "HALF", 5000);
    }
    throw err;
  }
}