Petter Måhlén's Blog

(This is item 3 in the code sharing cookbook)

Today, no CV comes along without “Scrum” and “Agile” on it and Scrum has gained acceptance so quickly that it should definitely set off any hype-warning systems. I personally think there’s a lot more to Scrum than just a hype – if you do it right, it’s extremely useful for productivity. There are some aspects of Scrum done right that are particularly valuable for sharing code:

• Empowering teams to deliver end-to-end functionality.
• (Relatively) short iterations.
• Delivering potentially shippable results with every sprint.

The biggest one is empowering teams to deliver fully functioning features. The way I think that affects code sharing is that rather than having your organisation focus on developing technology horizontals, you aim at developing feature verticals.

As much as feasible, Scrum tells you to have teams whose focus is to deliver the blue verticals in the above diagram. The red horizontals will be developed and maintained as a consequence of needs driven by the products. At the other end of the spectrum, your teams are aligned along the libraries or technology components, with each team responsible for one or more services or libraries. Obviously, you can vary your focus from totally red to totally blue, and you get different advantages and disadvantages depending on where you are. At the ‘red’ end of the spectrum, with teams very much aligned along technical component lines, you get the following advantages and disadvantages:

• Teams get a very deep knowledge of their components leading to solid, strong technology.
• Teams get a strong feeling of ownership of components, and can take a long view when developing them.
• You need to align product roadmaps for different products so that they can take advantage of features and changes made in the underlying libraries.
• You will get queues and blockages in the product development, where one team is waiting for the result of another team’s work, or where one team has finished its work and the result “sits on a shelf” until the downstream team is ready to pick it up. (This is what Lean tells you to avoid.)
• Most teams are not customer-facing, meaning that their priorities tend to shift from what is important to the business to what is important to their component. This in turn increases the risk of developing technology for its own sake rather than due to a business need.

At the ‘blue’ end, on the other hand, shared code is collectively owned by multiple teams and you get a situation where:

• Teams rarely need to wait for others in order to get their features finished and launched. This is great for innovation.
• The fact that there is never any waiting and the teams are typically in control of their own destiny is energising: nobody else is to blame for failures or gets credit for successes. Work done leads to something visible. This makes it more rewarding, fun and efficient.
• Features and changes that are developed are typically well aligned with business priorities.
• There is a real risk of under-investing in shared technology. Larger restructuring tasks may never happen because no single team owns the responsibility for technology components.
• There is no roadmap for individual components, which can lead to bloat and sprawl.
• The lack of continuity increases the risk that it is unclear how some feature was intended to work and the reasons why it was implemented in a certain way are more likely to be forgotten.
• Developers (by which I don’t mean just programmers, but all team members) need to be jacks-of-all-trades and risk being masters of none.

I think that the best solution in general is to get redder the deeper you go in the technology stack, because that’s where you have more complex and general technologies that a) need deep knowledge to develop and b) typically don’t affect end-user functionality very directly. I also think that most organisations I’ve seen have been too red. Having product-specific teams that are allowed to make modifications to much of the shared codebase allows you to develop your business-driving products quickly and based on their individual needs. So there should be more focus on products and teams that can develop features end-to-end, just as Scrum tells us!

The next thing that makes Scrum great for sharing code is the combination of time-limited sprints and the focus on delivering finished code at each iteration. The ‘deliver potentially shippable code’ bit seems to be one of the hardest things about Scrum, even though it is actually quite trivial as a concept: if you don’t feel like you could launch the code demoed at the end of the sprint the day after, don’t call the story done, and don’t grant yourself any story points for it. That way, you’ll not be able to let anything out of your sights until it is shippable and your velocity will be reduced until you’re great at getting things really ready – which is exactly right! If it is difficult for your team to take things all the way to potentially shippable because of environmental or process problems, then fix those issues until it is easy.

Actually finishing things is great for productivity in general, but it is even better in a code-sharing context. To illustrate how, I’ll use one of my favourite diagrams:

Assume you have three features to complete, each of which requires three tasks to be done. Each of the tasks takes one day, and you can only do one task at a time. If, as above, you start each feature as early as possible, all the code that is touched by feature A is in a ‘being modified’ state for 7 days (from the start of A1 to the end of A3), and the same applies to features B and C. In the second version below, the corresponding time is 3 days per feature, meaning that the risk that another team will need to make modifications concurrently is less than half of the first version.

Also, having any updates to shared code completed quickly means that the time between merge opportunities is decreased, which decreases the risks of isolation. You really want to shorten the branch – modify – merge back cycle as much as possible, and Scrum’s insistence on getting things production-ready within the time period of a single sprint (which is supposed to be less than 4 weeks – I’ve found that 2 or 3 weeks seems to work even better in most situations) is a great support in pushing for a short such cycle.

I think Scrum is great in general, and done right, it also helps you with sharing code. Jeff Sutherland said in a presentation I attended that the requirement to produce potentially shippable code with each iteration is the hardest requirement in the Nokia test. I can reluctantly understand why that’s the case. It’s not conceptually hard and unlike some classes of technical problem, it doesn’t require any exceptional talent to succeed with. What makes it hard is that it requires discipline and an environment where it is OK to flag up problems without management seeing that as being obstructive. It’s worth doing, so don’t allow yourself any shortcuts, and fix every process or environment obstacle that stands in the way of producing shippable code with each sprint. Combine that with teams that are empowered to own and modify pretty much all the code that makes up their product, and you’ve come a long way towards a great environment for code sharing.