Health checks (Terminus) in NestJS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this NestJS Terminus health check controller?

Consider this health check controller using Terminus in NestJS. What will the HTTP response body be when the /health endpoint is called?

NestJS

import { Controller, Get } from '@nestjs/common';
import { HealthCheck, HealthCheckService, HttpHealthIndicator } from '@nestjs/terminus';

@Controller('health')
export class HealthController {
  constructor(
    private health: HealthCheckService,
    private http: HttpHealthIndicator,
  ) {}

  @Get()
  @HealthCheck()
  check() {
    return this.health.check([
      () => this.http.pingCheck('nestjs-docs', 'https://docs.nestjs.com'),
    ]);
  }
}

A {"status":"error","info":{"nestjs-docs":{"status":"up"}},"error":{},"details":{"nestjs-docs":{"status":"up"}}}

B {"status":"error","info":{},"error":{"nestjs-docs":{"status":"down"}},"details":{"nestjs-docs":{"status":"down"}}}

C {"status":"ok","info":{"nestjs-docs":{"status":"down"}},"error":{},"details":{"nestjs-docs":{"status":"down"}}}

D {"status":"ok","info":{"nestjs-docs":{"status":"up"}},"error":{},"details":{"nestjs-docs":{"status":"up"}}}

💡 Hint

The pingCheck returns status 'up' if the URL is reachable.

The HealthCheckService returns a JSON with status 'ok' if all checks pass. The pingCheck to 'https://docs.nestjs.com' will succeed, so the status is 'up'.

📝 Syntax

intermediate

Which option causes a syntax error in this NestJS Terminus health check setup?

Identify which code snippet will cause a syntax error when defining a health check method in a NestJS controller using Terminus.

A

@HealthCheck()
check() {
  return this.health.check([
    () => this.http.pingCheck('google', 'https://google.com'),
  ]);
}

B

}
;)]  
,)'moc.elgoog//:sptth' ,'elgoog'(kcehCgnip.ptth.siht >= )(    
[(kcehc.htlaeh.siht nruter  
{ )(kcehc
)(kcehChtlaeH@

C

@HealthCheck
check() {
  return this.health.check([
    () => this.http.pingCheck('google', 'https://google.com'),
  ]);
}

D

@HealthCheck()
check() {
  return this.health.check([
    () => this.http.pingCheck('google', 'https://google.com')
  ]);
}

💡 Hint

Check if the decorator is properly called as a function.

The @HealthCheck decorator must be called with parentheses even if no arguments are passed. Omitting () causes a syntax error.

❓ state_output

advanced

What is the value of the 'status' field when a database health check fails?

Given this health check method in NestJS Terminus, what will be the 'status' field in the JSON response if the database ping fails?

NestJS

import { Controller, Get } from '@nestjs/common';
import { HealthCheck, HealthCheckService, TypeOrmHealthIndicator } from '@nestjs/terminus';

@Controller('health')
export class HealthController {
  constructor(
    private health: HealthCheckService,
    private db: TypeOrmHealthIndicator,
  ) {}

  @Get()
  @HealthCheck()
  check() {
    return this.health.check([
      () => this.db.pingCheck('database'),
    ]);
  }
}

A "error"

B "ok"

C "down"

D "unknown"

💡 Hint

The overall status is 'error' if any check fails.

If the database pingCheck fails, Terminus sets the overall status to 'error' in the response JSON.

🔧 Debug

advanced

Why does this Terminus health check always return status 'error'?

This health check always returns status 'error' even though the URL is correct. What is the likely cause?

NestJS

import { Controller, Get } from '@nestjs/common';
import { HealthCheck, HealthCheckService, HttpHealthIndicator } from '@nestjs/terminus';

@Controller('health')
export class HealthController {
  constructor(
    private health: HealthCheckService,
    private http: HttpHealthIndicator,
  ) {}

  @Get()
  @HealthCheck()
  check() {
    return this.health.check([
      () => this.http.pingCheck('nestjs-docs', 'https://docs.nestjs.com'),
      () => this.http.pingCheck('invalid-url', 'htp://invalid-url'),
    ]);
  }
}

A The second pingCheck URL has a typo in the protocol causing failure.

B The controller route 'health' is not registered.

C The @HealthCheck decorator is missing parentheses.

D The HealthCheckService is not injected properly.

💡 Hint

Check the URLs passed to pingCheck carefully.

The second pingCheck uses 'htp://' instead of 'http://', causing that check to fail and the overall status to be 'error'.

🧠 Conceptual

expert

Which option best describes how Terminus aggregates multiple health indicators?

In NestJS Terminus, when multiple health indicators are passed to HealthCheckService.check(), how is the overall health status determined?

A The overall status is always 'ok' regardless of individual indicator results.

B If all indicators return 'up', overall status is 'ok'; if any return 'down', overall status is 'error'.

C The overall status is 'error' only if all indicators return 'down'.

D The overall status is the status of the first indicator only.

💡 Hint

Think about how a system health check should behave if one part fails.

Terminus returns 'ok' only if all health indicators are 'up'. If any indicator fails (returns 'down'), the overall status is 'error'.