Always add context to your logs

August 12, 2017 | 4 Minute Read

Its a good rule of thumb to add context to your logs, if you dont believe lets see a simple case.

Broken Logs:

Imagine you have a system in which you run code asynchronously on diferent places.

You can have a webserver running, a page, if something goes wrong you log the exception:

  try {
    DoSomeWebServerStuff()
  }
  catch (Exception e) {
    Log.Error(e)
  }

Then you have on the same server notifications arriving asynchronously:

  try {
    HandleNotification()
  }
  catch (Exception e) {
    Log.Error(e)
  }

And also you have a service running somewhere, doing taks:

  try {
    DoServiceTask()
  }
  catch (Exception e) {
    Log.Error(e)
  }

We can already see that this smells really bad.

The problem with this approach is that when you want to actually debug something and see the logs, you will see something like this:

The Solution:

This is easily fixable by adding context to the log calls:

  try {
    DoSomeWebServerStuff()
  }
  catch (Exception e) {
    Log.Error(e)
  }

Becomes:

  try {
    DoSomeWebServerStuff()
  }
  catch (Exception e) {
    Log.ErrorFormat("DoSomeWebServerStuff Exception: {0}", e)
  }

  try {
    HandleNotification()
  }
  catch (Exception e) {
    Log.Error(e)
  }

Becomes:

  try {
    HandleNotification()
  }
  catch (Exception e) {
    Log.ErrorFormat("HandleNotification Exception: {0}", e)
  }

And

  try {
    DoServiceTask()
  }
  catch (Exception e) {
    Log.Error(e)
  }

Becomes:

  try {
    DoServiceTask()
  }
  catch (Exception e) {
    Log.ErrorFormat("DoServiceTask Exception: {0}", e)
  }

Now when you look at the logs you will see something like this:

A little bit more easy to read, and easier to find quickly and expand on the desired error.

Conclusion:

This is a very basic example, but its also a very basic concept.

And yes i know thats basically what the stack trace is for, but you can also add even MORE context like

Log.DebugFormat("HandleNotification: Type {0}, {1}", notifType, rawNotif")

or

Log.DebugFormat("DoSomeWebServerStuff Response From WebService X: {0}", resp.RawResponse)

Notes:

I consider having a huge try-catch an anti-pattern.
I also consider catching the root Exception object an anti-pattern.

But ill leave that for another article.