Twelve Factor App - Logs

The concept of the Twelve Factor app was developed by engineers at Heroku to describe the core principles and qualities that they believe are key to the adoption of the Software as a Service (SaaS) methodology.

First published in 2011 the Heroku platform is unashamedly opinionated in the enforcement of these principles, the relevance of them to effective software development has only intensified as the adoption of cloud computing has increased the number of us deploying and managing server side software.

The eleventh principle relates to the handling of logs:

"Applications should produce logs as event streams and leave the execution environment to aggregate"

The Importance of Logging

One of the primary mechanisms for monitoring the behaviour and operation of a deployed application is via logging. Exactly what is being logged will vary by application but log entries will relate to events and operations taking place within the application, this time ordered list presents a history of what has taken place both good and bad.

Often logging is an after thought with not as much attention being payed to it as probably should be given its importance in maintaining application health and performance. Whenever a developer needs to investigate any issue in the application, or to validate correct operation, they are likely to use the application logs as their primary source of information.

Aggregated Streams

For logs to be useful they need to be aggregated and stored. An app following twelve factor principles does not play a part in this aggregation and storage process, it simply ensures the flow of logging data through the standard output mechanism of the tech stack being employed (such as stdout).

This simplifies the approach to logging in the code base and allows for different logging strategies to be employed in different environments.

In a development environment a developer may simply review the logs in the terminal, while in production or staging environments the logs will be collected and managed by the infrastructure.

Log Management

This approach also opens up the possibility of going beyond simple file logging to use log management services that can increase the value that can be derived from the underlying data.

Tools such as Splunk, or any other big data solution, make it possible to collect large amounts of data that would be impractical if every aspect of logging had to be implemented within the application code base. Frameworks such as Serilog give the log data structure enabling it to be queried and mined for information that might be hard to glean by simply reading the entries as text.

Effective logging along with the ability to review the data it provides are important skills for any developer to learn. When an issue has struck and stakeholders are looking for answers than this skill we help you steer a course back towards a working system. 

The simpler the approach to logging is the more the data it produces can be relied upon. Many tools exist to help in this regard and ensuring your applications only role is to feed data in to the system will help to make this as simple as possible.