Logging is basically getting your program to write stuff down. You are already familiar with printing things out to the console or screen, logging is like that but on steroids.
Basically when a program runs in a production environment (for example, on a server on the cloud), logs let us keep track of what it is doing over time. A log is a series of messages that get printed or sent somewhere. They might be stored in a file, or sent over a network to a special logging service, or (during development) you might want to just see log messages on your screen.
A running program can be super opaque. Sometimes things break in really interesting ways and logs can be used to understand what actually happened that led up to the breakage. Sometimes logs need to be in place for generating metrics about system performance. Sometimes logs are used to understand security breaches.
Sometimes logs are just useful for a developer making some changes to a system. A dev can watch the log messages roll in and get a clear picture of what the code is doing.
Log messages come in a few different flavours called levels. Basically each log message is given a level (either implicitly or explicitly) and those levels mean different things. The different log levels tend to be pretty consistent between languages.
There are the main levels:
debug: Info for devs, these shouldn’t be logged on a production environment.info: This varies, basically there are usually a few different stakeholders involved in a project. These logs should add clarity without being overwhelmingly noisy.warn: Something looks really weird.error: Some error or exception has occured.critical or fatal: This is serious, immediate action required.As an analogy, if you shout “DON’T TOUCH THAT!” to a three year old about to put their hand on a stove then that might be a critical message. If you say “I’m going to the shop” then that might be an info message. If you say “I’m going to the shop to buy cigarettes” then that might be an error message.
Two major use cases for log levels are:
debug logs, but when you are developing then you do want to see them.warn log message then create a ticket on the bugtracker, and if there is a critical log message then sound the alarms.Different languages have different tooling that you can use to manage logs. To continue learning about logs, please follow the appropriate link below: