typescript 43 lines · 6 steps

Liveness vs readiness probes in NestJS

A NestJS health controller uses Terminus indicators to expose separate liveness and readiness endpoints.

Explained by highlit

NestJS Intermediate health-checks dependency-injection observability probes

1import { Controller, Get } from '@nestjs/common';
2import {
HealthCheck,
HealthCheckService,
TypeOrmHealthIndicator,
DiskHealthIndicator,
MemoryHealthIndicator,
8} from '@nestjs/terminus';
9import { ConfigService } from '@nestjs/config';
10 
11@Controller('health')
12export class HealthController {
constructor(
  private readonly health: HealthCheckService,
  private readonly db: TypeOrmHealthIndicator,
  private readonly disk: DiskHealthIndicator,
  private readonly memory: MemoryHealthIndicator,
  private readonly config: ConfigService,
) {}
20 
@Get('liveness')
@HealthCheck()
checkLiveness() {
  return this.health.check([
    () => this.memory.checkHeap('memory_heap', 300 * 1024 * 1024),
  ]);
}
28 
@Get('readiness')
@HealthCheck()
checkReadiness() {
  const path = this.config.get<string>('DISK_HEALTH_PATH', '/');
33 
  return this.health.check([
    () => this.db.pingCheck('database', { timeout: 1500 }),
    () =>
      this.disk.checkStorage('storage', {
        path,
        thresholdPercent: 0.9,
      }),
  ]);
}
43}

01 / 01

STEP 01

Walkthrough

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Three takeaways

1Liveness should stay cheap and self-contained while readiness verifies external dependencies you rely on.
2Passing indicator checks as arrow functions lets the health service run and aggregate them lazily.
3Separating the two probes lets orchestrators restart a hung process without pulling a busy one out of rotation.

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