What is a good solution structure to allow easy customisation of a product on a per client basis?

Question

I am looking for some advice on how to allow easy customisation and extension of a core product on a per client basis. I know it is probably too big a question. However we reall

Answer 1

I may not answer to this completly, but here some advices:

1. Don't copy your code, ever, whatever the reason is.
2. Don't rename the namespace to identify a given client version. Use the branches and continuous integration for that.
3. Choose a branching model like the following: a root branch called "Main", then create one branch from Main per major version of your product, then one branch per client. When you develop something, target from the start in which branch you'll develop depending on what you're doing (a client specific feature will go in the client branch, a global version in the version branch or client branch if you want to prototype it at first, etc.)
4. Try the best to rely on Work Item to track features you develop to know in which branch it's implemented to ease merge across branches.

Targeting the right branch for you dev is the most crucial thing, you don't have to necessary define some hard rules of "what to do in which occasion", but try to be consistant.

I've worked on a big 10 years project with more than 75 versions and what we usually did was:

• Next major version: create a new branch from Main, dev Inside
• Next minor version: dev in the current major branch, use Labels to mark each minor versions Inside your branch.
• Some complex functionnal features was developped in the branch of the client that asked for it, then reversed integrated in the version branch when we succeeded in "unbranded" it.
• Bug fixes in client branch, then reported in other branches when needed. (you have to use the Work Item for that or you'll get easily lost).

It's my take on that, other may have different point of view, I relied a lot on the Work Item for traceability of the code, which helped a lot for the delivery and reporting of code.

EDIT

Ok, I add some thought/feedback about branches:

In Software Configuration Management (SCM) you have two features to help you for versionning: branches and labels. Each one is not better nor worst than the other, it depends on what you need:

1. A Label is used to mark a point in time, using a label, for you to later be able to go back to that point if needed.
2. A Branch is used to "duplicate" your code to be able to work on two versions at the same time.

So using branches only depends on what you want to be able to do. If you have to work one many different versions (say one per client) at the same time: there's no other way to deal with it than using branches.

To limit the number of branches you have to decide what will be a new branch or what will be marked by a label for: Client Specific Versions, Major Version, Minor Version, Service Pack, etc.

Using branches for Client versions looks to be a no brainer. Using one branch for each Major version may be the toughest choice for you to make. If you choose to use only one branch for all major versions, then you won't have the flexibility to work on different major versions at the same time, but your number of branches will be the lowest possible.

Finally, Jemery Thompson has a good point when he says that not all your code should be client dependent, there are some libraries (typically the lowest level ones) that shouldn't be customized per client. What we do usually is using a separated branch tree (which is not per client) for Framework, cross-cutting, low level services libraries. Then reference these projects in the per client version projects.

My advice for you is using Nuget for these libraries and create nuget package for them, as it's the best way to define versionned dependencies. Defining a Nuget package is really easy, as well as setting up a local Nuget server.