Logging is one of the most important parts of software systems. Whether you have just started working on a new piece of software, or your system is running in a large scale production environment, you’ll always find yourself seeking help from log files. Logs are the first thing people look for when something goes wrong, or something doesn’t work as expected.

Logging the right information in the right way makes the life of developers so much easier. Two things that developers need to be aware of to get better at logging are what and how to log. In this article, we’ll take a look at the some of the basic logging etiquettes that can get us the best out of our logs.

The What and How of Logging

Let’s take the example of an e-commerce system and take a look at logging in Order Management Service (OMS).

Suppose a customer order fails due to an error from Inventory Management Service (IMS), a downstream service that OMS uses to verify the available inventory.

Let’s assume that OMS has already accepted an order, but during the final verification step, IMS returns the following error because the product is no longer available in the inventory.

HTTP/2 404 Product Not Available

What to Log

Normally, you would log the error in this way

log.error("Exception in fetching product information - {}", ex.getResponseBodyAsString())

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