Request ID

Because of a shared storage, CLS is an ideal tool for tracking request (correlation) IDs for the purpose of logging. This package provides an option to automatically generate request IDs in the middleware/guard/interceptor, if you pass { generateId: true } to its options. By default, the generated ID is a string based on Math.random(), but you can provide a custom function in the idGenerator option.

This function receives the Request (or the ExecutionContext in case the interceptor or the guard option is used) as the first parameter, which can be used in the generation process and should return (or resolve with) a string ID that will be stored in the CLS for later use.

Below is an example of retrieving the request ID from the request header with a fallback to an autogenerated one.

ClsModule.forRoot({
    middleware: {
        mount: true,
        generateId: true,
        idGenerator: (req: Request) =>
            req.headers['X-Request-Id'] ?? uuid();
    }
})

The ID is stored under the CLS_ID constant in the context. The ClsService provides a shorthand method getId to quickly retrieve it anywhere. It can be for example used in a custom logger:

my.logger.ts

@Injectable()
class MyLogger {
    constructor(private readonly cls: ClsService) {}

    log(message: string) {
        console.log(`<${this.cls.getId()}> ${message}`);
    }
}

Calling this from anywhere within a CLS context results in retrieving the ID:

my.service.ts

@Injectable()
class MyService {
    constructor(private readonly logger: MyLogger);

    hello() {
        this.logger.log('Hello');
        // -> logs for ex.: "<44c2d8ff-49a6-4244-869f-75a2df11517a> Hello"
    }
}