Health checks (Terminus) in NestJS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of health checks in a NestJS application using Terminus?

Health checks help monitor if the application and its dependencies are working correctly. Terminus provides easy ways to create these checks so the system can report its status.

beginner

How do you add a simple HTTP health check endpoint using Terminus in NestJS?

You create a controller with the @HealthCheck() decorator and use the HealthCheckService to run built-in checks like HTTP or database checks. This endpoint returns the status of the app.

intermediate

What is a 'readiness' health check and why is it important?

A readiness check tells if the app is ready to handle requests. It usually checks if dependencies like databases are connected. This helps load balancers send traffic only to ready instances.

intermediate

Explain how Terminus integrates with NestJS dependency injection for custom health indicators.

You create a custom health indicator class that extends HealthIndicator. Then you inject it into your health controller to include custom checks in the health endpoint.

intermediate

What is the difference between liveness and readiness probes in Terminus health checks?

Liveness probes check if the app is alive (not stuck or crashed). Readiness probes check if the app is ready to serve traffic (all dependencies are working). Both help Kubernetes manage app lifecycle.

Which decorator is used to mark a health check endpoint in NestJS Terminus?

A @CheckHealth()

B @GetHealth()

C @HealthCheck()

D @Health()

The @HealthCheck() decorator marks a method as a health check endpoint in Terminus.

What does a readiness probe typically check?

A If the app dependencies are connected and ready

B If the app process is running

C If the server CPU is below 50%

D If the app has received any requests

Readiness probes check if dependencies like databases are connected and the app can serve traffic.

How do you add a custom health check in Terminus?

A Create a custom HealthIndicator class and inject it

B Override the default health controller

C Use @CustomHealth() decorator

D Modify the main.ts file

You create a custom HealthIndicator class implementing HealthIndicator interface and inject it into the health controller.

Which service runs the health checks in a Terminus controller?

A HealthService

B HealthCheckService

C TerminusService

D CheckService

HealthCheckService runs the registered health indicators and returns the combined status.

What HTTP status code does a healthy Terminus endpoint usually return?

A 302 Redirect

B 404 Not Found

C 500 Internal Server Error

D 200 OK

A healthy status returns HTTP 200 OK to indicate the app is working properly.

Describe how you would implement a basic health check endpoint in a NestJS app using Terminus.

Think about the steps from module setup to controller method.

Explain the difference between liveness and readiness probes and why both are useful in a cloud environment.

Consider how Kubernetes uses these probes.