A feature toggle in
software development
Software development is the process of conceiving, specifying, designing, programming, documenting, testing, and bug fixing involved in creating and maintaining applications, frameworks, or other software components. Software development invol ...
provides an alternative to maintaining multiple
feature branches in
source code
In computing, source code, or simply code, is any collection of code, with or without comments, written using a human-readable programming language, usually as plain text. The source code of a program is specially designed to facilitate the wo ...
. A condition within the code enables or disables a
feature during
runtime. In agile settings the toggle is used in production, to switch on the feature on demand, for some or all the users. Thus, feature toggles do make it easier to
release
Release may refer to:
* Art release, the public distribution of an artistic production, such as a film, album, or song
* Legal release, a legal instrument
* News release, a communication directed at the news media
* Release (ISUP), a code to ident ...
often. Advanced roll out strategies such as canary roll out and
A/B testing are easier to handle.
Even if new releases are not
deployed to production continuously,
continuous delivery
Continuous delivery (CD) is a software engineering approach in which teams produce software in short cycles, ensuring that the software can be reliably released at any time and, following a pipeline through a "production-like environment", withou ...
is supported by feature toggles. The feature is integrated into the main branch before it is completed. The
version is deployed into a test environment once, the toggle allows to turn the feature on, and
test
Test(s), testing, or TEST may refer to:
* Test (assessment), an educational assessment intended to measure the respondents' knowledge or other abilities
Arts and entertainment
* ''Test'' (2013 film), an American film
* ''Test'' (2014 film), ...
it. Software integration cycles get shorter, and a version ready to go to production can be provided.
The third use of the technique is to allow developers to release a version of a product that has unfinished features. These unfinished features are hidden (toggled) so that they do not appear in the
user interface
In the industrial design field of human–computer interaction, a user interface (UI) is the space where interactions between humans and machines occur. The goal of this interaction is to allow effective operation and control of the machine f ...
. There is less effort to
merge
Merge, merging, or merger may refer to:
Concepts
* Merge (traffic), the reduction of the number of lanes on a road
* Merge (linguistics), a basic syntactic operation in generative syntax in the Minimalist Program
* Merger (politics), the comb ...
features into and out of the productive branch, and hence allows many small incremental versions of
software
Software is a set of computer programs and associated documentation and data. This is in contrast to hardware, from which the system is built and which actually performs the work.
At the lowest programming level, executable code consists ...
.
A feature toggle is also called feature switch, feature flag, feature gate, feature flipper, or conditional feature.
Implementation
Feature toggles are essentially
variables that are used inside
conditional statements. Therefore, the
blocks inside these conditional statements can be toggled 'on or off' depending on the value of the feature toggle. This allows developers to control the flow of their software and bypass features that are not ready for deployment. A block of code behind a runtime variable is usually still present and can be conditionally executed, sometimes within the same application lifecycle; a block of code behind a
preprocessor directive or
commented out would not be executable. A feature flag approach could use any of these methods to separate code paths in different phases of development.
The main usage of feature toggles is to avoid conflict that can arise when merging changes in software at the last moment before release, although this can lead to
toggle debt. Toggle debt arises due to the dead code present in software after a feature has been toggled on permanently and produces overhead. This portion of the code has to be removed carefully as to not disturb other parts of the code.
There are two main types of feature toggle. One is a release toggle, which the developer determines to either keep or remove before a product release depending on its working. The other is a business toggle, which is kept because it satisfies a different usage compared to that of the older code.
Feature toggles can be used in the following scenarios:
* Adding a new feature to an application.
* Enhancing an existing feature in an application.
* Hiding or disabling a feature.
* Extending an interface.
Feature toggles can be stored as:
* Row entries in a database.
* A property in a configuration file.
* An entry in an external feature flag service.
Feature groups
Feature groups consist of feature toggles that work together. This allows the developer to easily manage a set of related toggles.
Canary release
A canary release (or canary launch or canary deployment) allows developers to have features incrementally tested by a small set of users. Feature flags provide an alternate way to do canary launches and allow targeting by geographic locations or even user attributes. If a feature's performance is not satisfactory, then it can be rolled back without any adverse effects.
Martin Fowler states that a feature toggle "should be your last choice when you're dealing with putting features into production". Instead, it is best to break the feature into smaller parts that each can be implemented and safely introduced into the released product without causing other problems.
Feature-toggling is used by many large websites including Flickr, Disqus, Etsy, Reddit, Gmail and Netflix,
as well as software such as
Google Chrome Canary.
See also
*
Software configuration management
In software engineering, software configuration management (SCM or S/W CM) is the task of tracking and controlling changes in the software, part of the larger cross-disciplinary field of configuration management. SCM practices include revision ...
*
Software product line Software product lines (SPLs), or software product line development, refers to software engineering methods, tools and techniques for creating a collection of similar software systems from a shared set of software assets using a common means of pro ...
*
Comparison of open-source configuration management software
This is a comparison of notable free and open-source configuration management software, suitable for tasks like server configuration, orchestration and infrastructure as code typically performed by a system administrator.
Basic properties
" ...
References
{{Reflist
Software development process
Computer programming