Thursday, 15 May 2014

Feature Toggler – a Simple feature toggle library for .Net

So, you have decided to use Feature Toggling as your branching strategy. You don’t want the hassle of merging and branching and are confident that developers and testers can handle the additional complexity that comes with Feature Toggles. The next step is to decided how to go about using toggles. The simplest and most popular method of doing is to have feature toggles set in configuration files

Ideally, you would want a library that would take care of feature toggling. All you would need to do is to define the features and their toggle value in the configuration file and be able to check if a feature is available with a simple check. Some thing which for a configuration like below

    <add name="PrivateProfiles" toggle="on" />
    <add name="Photosharing" toggle="off" />
    <add name="Videos" toggle="1" />
    <add name="bookmarks" toggle="true" />

would allow having code like following

if (FeatureManager.HasFeature("PrivateProfiles")){


Having looked around, there were three libraries of note already available, which were

  1. NFeature
  2. FeatureToggle, and
  3. FeatureSwticher

This blog post gives a good comparison of them and their usability. Having used all three, I felt that all of them, though thorough, were overly complicated for the very simple scenario that I wanted to use. For example, NFeature requires you to create enumerations for all features added in configuration file.

I decided to create a new very simple feature toggling library.

The library is available as NuGet. Simply type “Install-package FeatureToggler” in the package manager window of your application. It will add references, add a configuration section in your configuration files and adds a few sample features in your configuration file.

Once you have the reference added, simply add features in the features collection and use them in your code using the FeatureManager.HasFeature(“”) method. Happy Coding!!

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Thursday, 8 May 2014

Feature Toggles and their limitations


This month's MSDN magazine contains an article on feature toggles. The subject has been close to my heart in the last few weeks and I have been weighing up whether they would work for our projects or not .

For those, who are unaware of the term, here is a good post by Martin Fowler describing feature toggles and their merits. He is convinced that feature toggles is the way forward and should be used instead of feature branches. Here is another great blog post explains the differences and recommends to use Feature toggles.

I love the idea of having no features branches … makes life easier. However, my take is that feature toggles is not for everyone and every team. For someone like Plural soft who does continuous delivery (and they use feature toggles), the process is simple. Each release, results in some new "features" being added. The process is generally additive with software becoming more "feature rich" and there is control on the release pipeline.

Now, turn our attention to a simple "message broker" kind application that interface with multiple systems and has no UI. The application handles message say M1 from one applications, does something to it and pass on message M2 to another application. Now, let's say there is a change in message interface because the sending application is changing. We start with a feature to handle the new message interface. Since, the change is a few months away, we need to keep supporting the existing interface. In this case, if feature toggling is involved, we would have to create a parallel code path to handle the new message interface and direct to that code path with feature toggle. If it wasn't the case and we were using branching instead, the change in code would have been much simpler. So in essence, we have replaced the complexity of merging by having a more complex code change.

Take another example, this time we have to delete something from the application, let's say a web service from the system. The feature toggle mechanism would require us to modify it to error on invocation when the feature is on. Compare it with the alternative of removing the service altogether.

Similarly, let's consider a windows/web UI application. One of the features is to re-design of the screens. The redesign includes jigging around all the form controls and include some new graphics. With feature toggling approach, we will either have a condition on display of each of these changes or have a new form created altogether, choosing between the two based on toggle value.

These were only some of the scenarios where feature toggle wouldn't essentially simplify things in my opinion. Others might disagree and I would love to listen to them, so please post your comments if you have any.


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