TTL configuration in NestJS - Mini Project: Build & Apply

TTL Configuration in NestJS Cache Module

📖 Scenario: You are building a NestJS application that caches user data to improve performance. You want to configure the cache so that cached data expires automatically after a certain time (TTL - Time To Live).

🎯 Goal: Configure the NestJS CacheModule with a TTL of 5 seconds and create a service that caches and retrieves user data.

📋 What You'll Learn

Import CacheModule with TTL configuration set to 5 seconds

Create a service called UserCacheService

Use cacheManager to set and get cached user data

Ensure cached data expires after 5 seconds automatically

💡 Why This Matters

🌍 Real World

Caching user data with TTL helps improve app performance by reducing repeated database calls and automatically cleaning up stale data.

💼 Career

Understanding TTL configuration and cache management is essential for backend developers working with NestJS to build scalable and efficient applications.

1

Import CacheModule with TTL configuration

In your AppModule, import CacheModule from @nestjs/cache-manager and configure it with ttl: 5 inside CacheModule.register().

NestJS

import { Module } from '@nestjs/common';
import { CacheModule } from '@nestjs/cache-manager';

@Module({
  imports: [
    // Register CacheModule with TTL 5 seconds
  ],
})
export class AppModule {}

Hint

Use CacheModule.register({ ttl: 5 }) inside the imports array of @Module.

2

Create UserCacheService with cacheManager injection

Create a service class called UserCacheService. Inject CACHE_MANAGER using @Inject and assign it to a private variable called cacheManager.

NestJS

import { Injectable, Inject, CACHE_MANAGER } from '@nestjs/common';
import { Cache } from 'cache-manager';

@Injectable()
export class UserCacheService {
  constructor(
    // Inject CACHE_MANAGER here
  ) {}
}

Hint

Use @Inject(CACHE_MANAGER) in the constructor to get the cache manager instance.

3

Add methods to set and get cached user data

Inside UserCacheService, add an async method cacheUserData that takes userId and data and uses this.cacheManager.set() to cache the data. Also add an async method getUserData that takes userId and returns cached data using this.cacheManager.get().

NestJS

import { Injectable, Inject, CACHE_MANAGER } from '@nestjs/common';
import { Cache } from 'cache-manager';

@Injectable()
export class UserCacheService {
  constructor(
    @Inject(CACHE_MANAGER) private cacheManager: Cache,
  ) {}

  // Add async cacheUserData(userId: string, data: any) method
  // Add async getUserData(userId: string) method
}

Hint

Use this.cacheManager.set(key, value) to store and this.cacheManager.get(key) to retrieve cached data.

4

Register UserCacheService in AppModule providers

Add UserCacheService to the providers array in AppModule so it can be injected and used in the application.

NestJS

import { Module } from '@nestjs/common';
import { CacheModule } from '@nestjs/cache-manager';
import { UserCacheService } from './user-cache.service';

@Module({
  imports: [
    CacheModule.register({ ttl: 5 }),
  ],
  // Add UserCacheService to providers array
})
export class AppModule {}

// UserCacheService code remains unchanged

Hint

Add UserCacheService inside the providers array of @Module.

Practice

1. What does TTL stand for in NestJS caching configuration?

easy

A. Timed Token Lock, a security feature for cache access

B. Time To Live, the duration cached data stays before removal

C. Temporary Transfer Lock, a pause on cache updates

D. Total Transaction Limit, the max number of cache writes

Solution

1. Step 1: Understand TTL meaning in caching

   TTL means how long cached data remains valid before it is removed automatically.

2. Step 2: Match TTL to the correct full form

   TTL stands for Time To Live, which fits the caching context perfectly.

3. Final Answer:

   Time To Live, the duration cached data stays before removal -> Option B

4. Quick Check:

   TTL = Time To Live [OK]

Hint: TTL means how long cache data lives before removal [OK]

Common Mistakes:

• Confusing TTL with security or transaction terms
• Thinking TTL is a cache size limit
• Assuming TTL is a manual cache clear command

2. Which is the correct way to set a global TTL of 10 seconds in NestJS cache module?

easy

A. CacheModule.register({ ttl: 10 })

B. CacheModule.register({ timeToLive: 10 })

C. CacheModule.register({ ttl: 10000 })

D. CacheModule.register({ expire: 10 })

Solution

1. Step 1: Identify TTL unit in NestJS cache config

   TTL is set in seconds, so 10 means 10 seconds.

2. Step 2: Check correct property name and value type

   The property is ttl, and the value is a number in seconds, so ttl: 10 is correct.

3. Final Answer:

   CacheModule.register({ ttl: 10 }) -> Option A

4. Quick Check:

   TTL in seconds uses 'ttl' property [OK]

Hint: TTL value is seconds, use 'ttl' property exactly [OK]

Common Mistakes:

• Using milliseconds instead of seconds
• Using wrong property names like timeToLive or expire
• Passing ttl as string instead of number

3. Given this NestJS cache config snippet:

CacheModule.register({ ttl: 5 })

What happens to cached data after 6 seconds?

medium

A. Cached data throws an error after 6 seconds

B. Cached data remains indefinitely until manually cleared

C. Cached data is refreshed automatically every 6 seconds

D. Cached data is automatically removed after 5 seconds

Solution

1. Step 1: Understand TTL effect on cached data

   TTL of 5 means cached data expires and is removed after 5 seconds.

2. Step 2: Check what happens after 6 seconds

   Since 6 seconds is more than 5, cached data is no longer valid and is removed.

3. Final Answer:

   Cached data is automatically removed after 5 seconds -> Option D

4. Quick Check:

   TTL 5 seconds means removal after 5 seconds [OK]

Hint: Data expires after TTL seconds, so 6 > 5 means removal [OK]

Common Mistakes:

• Thinking data stays forever without manual clear
• Assuming TTL refreshes cache automatically
• Believing cache throws errors on expiry

4. Identify the error in this NestJS cache TTL setup:

CacheModule.register({ ttl: '30' })

medium

A. TTL property name is incorrect, should be timeToLive

B. TTL cannot be set globally, only per item

C. TTL value should be a number, not a string

D. TTL value must be in milliseconds, not seconds

Solution

1. Step 1: Check TTL value type

   TTL expects a number representing seconds, but '30' is a string.

2. Step 2: Confirm correct property and units

   The property ttl is correct and uses seconds, so only the value type is wrong.

3. Final Answer:

   TTL value should be a number, not a string -> Option C

4. Quick Check:

   TTL must be numeric seconds, not string [OK]

Hint: TTL must be a number, not quoted string [OK]

Common Mistakes:

• Using string instead of number for TTL
• Changing property name incorrectly
• Confusing seconds with milliseconds

5. You want to cache user data with a TTL of 60 seconds, but override it to 120 seconds for admin users only. How do you configure TTL in NestJS?

hard

A. Set global TTL to 60, then use @CacheTTL(120) decorator on admin methods

B. Set global TTL to 120, then manually clear cache for non-admin users

C. Set TTL only in controller constructor based on user role

D. Use two separate CacheModules with different TTLs and switch dynamically

Solution

1. Step 1: Set global TTL for general users

   Configure CacheModule with ttl: 60 to cover normal users.

2. Step 2: Override TTL for admin users

   Use the @CacheTTL(120) decorator on admin-specific methods to extend TTL.

3. Final Answer:

   Set global TTL to 60, then use @CacheTTL(120) decorator on admin methods -> Option A

4. Quick Check:

   Global TTL + @CacheTTL override [OK]

Hint: Use global TTL plus @CacheTTL decorator for overrides [OK]

Common Mistakes:

• Trying to set TTL only in constructor without decorators
• Using multiple CacheModules unnecessarily
• Setting global TTL too high and clearing cache manually