Loki

Loki is a generic logging library for Swift applications. It supports asynchronous logging, multiple destinations and also offers some default destination for logging.

Usage

You can import and use it like so,

import Loki

Loki.sourceName = "Foobar"  // Name of the app (optional)

let console = ConsoleDestination()  // define console destination (stdout)
console.logLevle = .info            // default (supports 4 other levels)
Loki.addDestination(console)

let file = FileDestination()
Loki.url = URL(fileWithURLPath: "/tmp/foo.log")
Loki.addDestination(file)   // log to file

// Now you can log stuff
Loki.info("Hola!")

This logs something like below in console and the file,

INFO: Hola!

Global logging

You may have multiple services in your platform, and you cannot pay a visit to all the services all the time. When it comes to microservices, you need a centralized logging service.

There are multiple options.

If you don't have a lot of services, then you can share the volume, and maintain a shared log file (like /var/global.log). In such a case, all the applications could have the same file destination.

On the other hand, if you have a lot of services, then it makes sense to have a HTTP destination. That's where LokiCollector comes in. It serves as your centralized logging service.

import Loki

let console = ConsoleDestination()
Loki.addDestination(console)
console.logLevel = .info   // filter log messages on the server end

// Spin up the server with an (optional) authorization check.
LokiCollector.start(listenPort: 8000, authorizeWith: "foobar")

Assuming the service address is 1.2.3.4, we can now do the following in the application.

let httpClient = HTTPDestination(url: "http://1.2.3.4:8000")
httpClient.hostAuth = "foobar"
Loki.addDestination(httpClient)

Loki.error("Whee!")

This logs something like below in the service console,

Error: Whee!