Logging

Cookie Cutter comes with its own logging abstraction that is used throughout the framework and recommended to be used by services built with Cookie Cutter as well.

export interface ILoggerStructuredData {
    [key: string]: any;
}

export interface ILogger {
    info(message: string, data?: ILoggerStructuredData): void;
    debug(message: string, data?: ILoggerStructuredData): void;
    warn(message: string, data?: ILoggerStructuredData): void;
    error(message: string, err?: any, data?: ILoggerStructuredData): void;
}

The core framework ships with a NullLogger (the default, that will not print any logs) and a ConsoleLogger that will write all log messages to stdout.

Application.create()
    .logger(new ConsoleLogger())
    // ...
    .run();

Message Handlers can gain access to the logger via the DispatchContext

function onMyInput(msg: IMyInput, ctx: IDispatchContext): void {
    ctx.logger.info("processing a message", {
        customerId: msg.customerId,
    });
}

In combination with the ConsoleLogger the snipped above would print the following to stdout

2019-05-16T15:57:05.284Z |  INFO | processing a message | customerId=4123
2019-05-16T15:57:07.214Z |  INFO | processing a message | customerId=2641

Log messages emitted in the context of a message handler will automatically add all metadata of the input message as structured log data.

function onMyKafkaInput(msg: IMyKafkaInput, ctx: IDispatchContext): void {
    ctx.logger.info("processing a message from Kafka", {
        customerId: msg.customerId,
    });
}

2019-05-16T15:57:05.284Z |  INFO | processing a message from Kafka | customerId=4123 | topic=my-topic | partition=1 | offset=273471

The log level can be configured during application setup

Application.create()
    .logger(new ConsoleLogger(), LogLevel.Warning)
    // ...
    .run();

This will only print log messages that are Warning or higher. The default log level is Debug.

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