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NestJS Enterprise Backend APIs · 강의

인터셉터를 활용한 시간 초과, 재시도 및 격벽

RxJS 기반 시간 초과·재시도 인터셉터와 외부 호출을 위한 동시성 격벽을 구현합니다.

레슨 1/413개 단계

인터셉터를 활용한 시간 초과, 재시도 및 격벽은(는) CoddyKit의 무료 NestJS Enterprise Backend APIs 강의입니다. 이것은 4개 중 1번째 강의입니다. 아래에서 전체 강의를 무료로 읽을 수 있으며, 내장 코드 에디터와 24/7 AI 튜터와 함께 브라우저에서 직접 실습할 수 있습니다. 이 강의는 NestJS Enterprise Backend APIs 학습 경로의 일부이며, 진행 상황이 웹과 CoddyKit 앱에 동기화됩니다. NestJS Enterprise Backend APIs 강의에는 총 4개의 강의가 포함되어 있습니다.

이 강의의 일부는 아직 번역되지 않았으며 영어로 표시됩니다.

Why Resilience Patterns Belong in Interceptors

Outbound calls to other services fail in three classic ways: they hang forever, they fail transiently, or they flood a slow dependency until it (and you) collapse. The three matching defenses are timeouts, retries, and bulkheads.

  • Timeout — cap how long any one call may run.
  • Retry — re-attempt a failed call a bounded number of times, ideally only for transient errors.
  • Bulkhead — cap how many calls run concurrently so one dependency can't exhaust your resources.

In NestJS these compose cleanly as NestInterceptors. An interceptor wraps the handler's RxJS stream, so we can layer timeout and retry operators on the response Observable without touching business logic.

The Interceptor Contract

A NestJS interceptor implements intercept(context, next) and returns an Observable. Calling next.handle() runs the route handler and gives you its result stream. Anything you pipe onto that stream — timeout, retry, catchError — applies to the response.

  • This is why resilience logic lives here: it is cross-cutting and stream-based.
  • Operators run in order, so placement of timeout vs retry changes behavior — we will exploit that.
import { CallHandler, ExecutionContext, Injectable, NestInterceptor } from '@nestjs/common';
import { Observable } from 'rxjs';
import { tap } from 'rxjs/operators';

@Injectable()
export class LoggingInterceptor implements NestInterceptor {
  intercept(ctx: ExecutionContext, next: CallHandler): Observable<unknown> {
    const started = Date.now();
    // next.handle() executes the route handler; we pipe onto its stream.
    return next.handle().pipe(
      tap(() => console.log(`took ${Date.now() - started}ms`)),
    );
  }
}

A Timeout Interceptor

The RxJS timeout operator emits a TimeoutError if the source does not emit within the given window. We catch that error and convert it into a proper HTTP response — 504 Gateway Timeout — instead of leaking an RxJS error class.

  • Always translate TimeoutError into a meaningful status; an unhandled one becomes a generic 500.
  • Re-throw anything that is not a timeout so other filters can handle it.
import { CallHandler, ExecutionContext, Injectable, NestInterceptor, RequestTimeoutException } from '@nestjs/common';
import { Observable, TimeoutError, throwError } from 'rxjs';
import { catchError, timeout } from 'rxjs/operators';

@Injectable()
export class TimeoutInterceptor implements NestInterceptor {
  constructor(private readonly ms = 5000) {}

  intercept(_ctx: ExecutionContext, next: CallHandler): Observable<unknown> {
    return next.handle().pipe(
      timeout(this.ms),
      catchError((err) =>
        err instanceof TimeoutError
          ? throwError(() => new RequestTimeoutException('Upstream call timed out'))
          : throwError(() => err),
      ),
    );
  }
}

Making the Timeout Configurable Per Route

A flat 5s timeout rarely fits every endpoint. Expose the value via metadata so each handler can override it. Read it with Reflector, falling back to a default.

  • Define a @Timeout(ms) decorator using SetMetadata.
  • The interceptor pulls the value off the handler with reflector.get.

This keeps the policy declarative: the route says how patient it is.

import { SetMetadata, applyDecorators } from '@nestjs/common';

export const TIMEOUT_MS = 'timeout_ms';
export const Timeout = (ms: number) => applyDecorators(SetMetadata(TIMEOUT_MS, ms));

// In the interceptor:
// const ms = this.reflector.get<number>(TIMEOUT_MS, ctx.getHandler()) ?? 5000;
// return next.handle().pipe(timeout(ms), /* catchError ... */);

Retrying Transient Failures

RxJS retry resubscribes to the source when it errors. Naive retry(3) hammers a struggling dependency. Use retry({ count, delay }) where delay is a function returning an Observable — this lets us add exponential backoff with jitter and filter which errors are retryable.

  • Retry only idempotent operations (GET, PUT, DELETE) — never blind-retry a POST that may have already succeeded.
  • Retry only transient errors: timeouts, 502/503/504, connection resets — not a 400 or 422.
import { Observable, throwError, timer } from 'rxjs';
import { retry } from 'rxjs/operators';

const RETRYABLE = new Set([502, 503, 504]);

function withRetry<T>(source: Observable<T>): Observable<T> {
  return source.pipe(
    retry({
      count: 3,
      delay: (err, attempt) => {
        const status = err?.response?.status;
        if (status && !RETRYABLE.has(status)) return throwError(() => err);
        const base = 100 * 2 ** (attempt - 1); // 100, 200, 400 ms
        const jitter = Math.random() * base;
        return timer(base + jitter);
      },
    }),
  );
}

Backoff Math, Standalone

Before wiring backoff into an interceptor, it helps to see the delays. Full jitter picks a random delay in [0, base] to spread retries and avoid the thundering herd where every client retries at the same instant.

This snippet just prints the schedule — pure TypeScript, no framework.

function backoffSchedule(maxAttempts: number, baseMs: number): number[] {
  const delays: number[] = [];
  for (let attempt = 1; attempt <= maxAttempts; attempt++) {
    const cap = baseMs * 2 ** (attempt - 1);
    const fullJitter = Math.floor(Math.random() * cap); // [0, cap)
    delays.push(fullJitter);
  }
  return delays;
}

const schedule = backoffSchedule(5, 100);
console.log('Caps:   ', [100, 200, 400, 800, 1600].join(', '));
console.log('Jittered:', schedule.join(', '));
console.log('Total wait:', schedule.reduce((a, b) => a + b, 0), 'ms');

Ordering: Timeout Inside, Retry Outside

Operator order is the subtle part. Put timeout before retry in the pipe so each attempt gets its own deadline; retry then resubscribes and re-arms the timeout for the next attempt.

  • timeout then retry — per-attempt deadline, N fresh tries. Usually what you want.
  • retry then timeout — one deadline spanning all attempts; a slow first try eats the whole budget.

Always bound the worst case: attempts × (timeout + maxBackoff) must stay under the caller's own deadline.

import { CallHandler, ExecutionContext, Injectable, NestInterceptor, RequestTimeoutException } from '@nestjs/common';
import { Observable, TimeoutError, throwError, timer } from 'rxjs';
import { catchError, retry, timeout } from 'rxjs/operators';

@Injectable()
export class ResilientInterceptor implements NestInterceptor {
  intercept(_ctx: ExecutionContext, next: CallHandler): Observable<unknown> {
    return next.handle().pipe(
      timeout(2000),               // per-attempt deadline
      retry({ count: 3, delay: (_e, n) => timer(100 * 2 ** (n - 1)) }),
      catchError((err) =>
        err instanceof TimeoutError
          ? throwError(() => new RequestTimeoutException())
          : throwError(() => err),
      ),
    );
  }
}

The Bulkhead: Capping Concurrency

Timeouts and retries protect a single request. A bulkhead protects the whole process: it limits how many in-flight calls a dependency may have, so a slow downstream can't pile up unbounded promises and exhaust threads, sockets, or memory.

  • Calls beyond the limit either queue (bounded) or are rejected fast (503).
  • Named after ship compartments: a flood in one section is sealed off from the rest.

A minimal bulkhead is a semaphore: a permit count plus a waiter queue.

export class Bulkhead {
  private active = 0;
  private readonly queue: Array<() => void> = [];

  constructor(private readonly maxConcurrent: number, private readonly maxQueue: number) {}

  async run<T>(task: () => Promise<T>): Promise<T> {
    if (this.active >= this.maxConcurrent) {
      if (this.queue.length >= this.maxQueue) throw new Error('BULKHEAD_FULL');
      await new Promise<void>((resolve) => this.queue.push(resolve));
    }
    this.active++;
    try {
      return await task();
    } finally {
      this.active--;
      this.queue.shift()?.();
    }
  }
}

A Runnable Bulkhead Simulation

Here is the bulkhead exercised end-to-end with simulated async work. Watch that no more than maxConcurrent tasks run at once, and overflow past the queue is rejected immediately — the fast-fail that keeps your service healthy.

class Bulkhead {
  private active = 0;
  private queue: Array<() => void> = [];
  constructor(private max: number, private maxQueue: number) {}
  async run<T>(task: () => Promise<T>): Promise<T> {
    if (this.active >= this.max) {
      if (this.queue.length >= this.maxQueue) throw new Error('BULKHEAD_FULL');
      await new Promise<void>((r) => this.queue.push(r));
    }
    this.active++;
    try { return await task(); }
    finally { this.active--; this.queue.shift()?.(); }
  }
}

const sleep = (ms: number) => new Promise((r) => setTimeout(r, ms));
const bh = new Bulkhead(2, 1);
let peak = 0, running = 0;

async function call(id: number) {
  try {
    await bh.run(async () => {
      running++; peak = Math.max(peak, running);
      await sleep(50);
      running--;
    });
    return `ok-${id}`;
  } catch (e) { return `rejected-${id}`; }
}

async function main() {
  const results = await Promise.all([1, 2, 3, 4, 5].map(call));
  console.log(results.join(', '));
  console.log('peak concurrency:', peak);
}
main();

Wiring the Bulkhead into an Interceptor

To apply a bulkhead per outbound dependency, hold a Bulkhead instance in a provider and run the handler stream through it. Use from(promise) to bridge the async run() back into RxJS, then layer timeout and retry on top.

  • One bulkhead instance per dependency, not per request — the limit is shared, so it must be a singleton provider.
  • Convert BULKHEAD_FULL into 503 Service Unavailable so callers can back off.
import { CallHandler, ExecutionContext, Injectable, NestInterceptor, ServiceUnavailableException } from '@nestjs/common';
import { Observable, defer, lastValueFrom } from 'rxjs';
import { catchError } from 'rxjs/operators';
import { Bulkhead } from './bulkhead';

@Injectable()
export class BulkheadInterceptor implements NestInterceptor {
  private readonly bulkhead = new Bulkhead(10, 20); // shared, singleton-scoped

  intercept(_ctx: ExecutionContext, next: CallHandler): Observable<unknown> {
    return defer(() => this.bulkhead.run(() => lastValueFrom(next.handle()))).pipe(
      catchError((err) => {
        if (err?.message === 'BULKHEAD_FULL') throw new ServiceUnavailableException('Capacity reached');
        throw err;
      }),
    );
  }
}

Composing All Three at the HttpModule Layer

In practice you rarely intercept inbound routes for outbound resilience — you wrap the HTTP client. With Nest's HttpService (Axios + RxJS) you pipe the same operators onto each outbound observable, and run it through the dependency's bulkhead.

  • Tune budgets per dependency: a fast cache gets a 200ms timeout; a report API gets 10s and zero retries.
  • Pair this with a circuit breaker so a dependency that keeps failing is shed before timeouts even fire.
import { Injectable } from '@nestjs/common';
import { HttpService } from '@nestjs/axios';
import { AxiosResponse } from 'axios';
import { Observable, defer, lastValueFrom, throwError, timer } from 'rxjs';
import { retry, timeout } from 'rxjs/operators';
import { Bulkhead } from './bulkhead';

@Injectable()
export class PricingClient {
  private readonly bulkhead = new Bulkhead(8, 16);
  constructor(private readonly http: HttpService) {}

  getPrice(sku: string): Observable<AxiosResponse> {
    return defer(() =>
      this.bulkhead.run(() =>
        lastValueFrom(
          this.http.get(`/pricing/${sku}`).pipe(
            timeout(800),
            retry({ count: 2, delay: (_e, n) => timer(100 * 2 ** (n - 1)) }),
          ),
        ),
      ),
    );
  }
}

Quick Check

You wrap an outbound call with both a 2s timeout and a 3-attempt retry inside one RxJS pipe. You want each attempt to have its own 2-second deadline. Which operator ordering achieves that?

인터랙티브 레슨에서 답해보세요

Recap

You built the three core outbound-resilience patterns as composable NestJS interceptors:

  • Timeout — timeout(ms) + catchError to translate TimeoutError into 504/408; make it per-route via Reflector metadata.
  • Retry — retry({ count, delay }) with exponential backoff and full jitter, restricted to idempotent operations and transient status codes.
  • Bulkhead — a semaphore (active count + bounded queue) per dependency that fast-fails with 503 when capacity is reached, isolating one slow downstream.

Key decisions: place timeout before retry for per-attempt deadlines; keep bulkheads singleton-scoped per dependency; and always bound the worst case (attempts × (timeout + backoff)) below the caller's deadline. Combine these with a circuit breaker for full steady-state protection.

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자주 묻는 질문

“인터셉터를 활용한 시간 초과, 재시도 및 격벽” 강의는 무료인가요?

네 — “인터셉터를 활용한 시간 초과, 재시도 및 격벽” 전체 내용을 이 웹사이트에서 무료로 읽을 수 있습니다. 인터랙티브하게 실습하려면(내장 코드 에디터와 24/7 AI 튜터), CoddyKit PRO로 업그레이드하면 NestJS Enterprise Backend APIs 강의 전체를 잠금 해제할 수 있습니다. NestJS Enterprise Backend APIs 강의에는 총 4개의 강의가 포함되어 있습니다.

“인터셉터를 활용한 시간 초과, 재시도 및 격벽”에서 뭘 배우나요?

RxJS 기반 시간 초과·재시도 인터셉터와 외부 호출을 위한 동시성 격벽을 구현합니다. 브라우저에서 직접 실행하는 실습 코드로 NestJS Enterprise Backend APIs을(를) 배우며, 24/7 AI 튜터가 강의를 진행하면서 질문에 답변해줍니다.

NestJS Enterprise Backend APIs을(를) 시작하는 데 경험이 필요한가요?

사전 경험은 필요하지 않습니다. CoddyKit의 NestJS Enterprise Backend APIs은(는) 초급자부터 고급 학습자까지를 위해 구성되어 있으므로, 여기서 시작하거나 처음부터 시작할 수 있으며 자신의 속도대로 진행할 수 있습니다. 이것은 4개 중 1번째 강의입니다.

“인터셉터를 활용한 시간 초과, 재시도 및 격벽” 강의는 얼마나 걸리나요?

대부분의 CoddyKit 강의는 약 5~10분이 소요됩니다. 각 강의는 간결하고 인터랙티브하여 꾸준한 진행이 가능하며, 웹과 앱에서 중단한 부분부터 바로 시작할 수 있습니다.

이 NestJS Enterprise Backend APIs 강의에서 코드를 작성하고 실행할 수 있나요?

네. 모든 NestJS Enterprise Backend APIs 강의에는 내장 코드 에디터가 포함되어 있으므로, 브라우저에서 바로 실제 코드를 작성하고 실행한 후 즉시 AI 피드백을 받을 수 있습니다 — 로컬 설정이 필요 없습니다.

이 강의의 모든 강의

  1. 인터셉터를 활용한 시간 초과, 재시도 및 격벽
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  3. OpenTelemetry를 활용한 분산 추적
  4. SLO와 오류 예산 정의
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