There are a number of software teams and organizations that think they should choose between Kanban and Scrum as their software development process. This is a GIANT and RISKY mistake, in my professional opinion.
It’s not an either/or proposition. Scrum is about software development. Kanban is about change management.
There are several reasons why choosing Kanban as your team’s software development process is a mistake.
1. You are applying Kanban to the incorrect context.
Would you use a hammer to insert a screw in a wall? You can, but you’ll probably damage your wall in the process, and the same is true of Kanban as a software development approach. David Anderson, the creator of The Kanban Method, has apparently said this over and over again since 2005, but no one seems to listen.
Don’t take my word for it, listen to David:
“Kanban is NOT a software development life cycle or project management methodology! It is not a way of making software or running projects that make software!” — David Anderson
“There is no kanban process for software development. At least I am not aware of one. I have never published one.” — David Anderson
“It is actually not possible to develop with only Kanban. The Kanban Method by itself does not contain practices sufficient to do product development.” — David Anderson*
(*The first two came from the “over and over..” link above. The last quote was sent to me via email from someone at David’s company. I think they just pasted in something David had already written)
I should also mention that others have mentioned to me that David talks out of both sides of his mouth about Kanban, Agile, and software development, perhaps trying to capitalize on the fame and success of Agile software development. That may be true, but it may also be true that David has been saying all of these things for years and no one is paying attention to what he says, which is unfortunate.
2. Kanban is modeled more after the assembly line and manufacturing. Scrum is modeled more after creative product design.
Which do you think more closely resembles software development? Laverne and Shirley on the assembly line at the Shotz Brewery? Or the group of NASA engineers on the ground who saved the lives of the Apollo 13 astronauts by coming up with a creative solution to a problem within a time-box? If you think software rolls off of an assembly line, then I think that it is unfortunate that you’ve never worked in a creative software development environment — it’s AWESOME!
Maybe my Laverne and Shirley reference is oversimplified. The reason to use Scrum instead of Kanban for software development delves down into process control theory, and the difference between a “defined process” and an “empirical process.” In short, a defined process works better when the inputs and outputs to the process are well known and repeatable (like a manufacturing line). An empirical process works better when the inputs and outputs to the process are less known and very difficult to repeat. No two software features are alike. This is why it’s darned near impossible to measure software productivity directly, even though some naive “bean counters” still try to. Like the stock market, no one metric will predict it accurately, but a range of indicators can help predict it more accurately. So, in summary, Scrum is based on empirical processes like product design.
One of the very key parts of empirical processes is the characteristic of inspecting and adapting the product. Think of yourself making a pot of soup from scratch, without a recipe. Think about all of the “taste-tweak ingredients-taste” experiments(feedback loops) you would need to get a pot of soup that tastes good.
Scrum has the frequent feedback loops built in, for a variety of audiences(Dev Team, Product Owner, Stakeholders, Users) , and for a variety of topics(process-Sprint Retro, product-Ordered Product Backlog, product-Sprint Review, product-Valuable/Releasable Increments). Kanban has no such built in loops, but again, that’s because it wasn’t designed for software development!
3. From a Complexity Science view, Kanban is for ‘complicated’ work while Scrum is for “complex” work.
I know the Kanban folks don’t like hearing this, but I think Ken Schwaber was right when he said this, and I think history will prove him right about Kanban as it was described in David Anderson’s book. In short, the Cynefin model defines 5 domains, of which 2 of them are “complicated” and “complex” work.
‘Complicated’ work is best solved via ‘good practice’ and ‘experts’ who can find ’cause and effect’ fairly easily. When I think of ‘complicated’ work, I think of an the IT support person who sets up your computer or trouble shoots it. Yes, you need an expert to solve these problems, and the vast majority of the time, the steps to solve these kinds of problems are fairly consistent and repeatable. They are not exactlyrepeatable, just mostly repeatable. If the steps were exactly repeatable then they would fall into the ‘Simple’ domain of Cynefin.
‘Complex’ work is best solved via ‘safe to fail experiments’ and one can only ascertain cause and effect after the fact. Each Sprint in Scrum is a ‘safe to fail’ experiment because, while the Sprint increment is always releasable, the business side of the house makes the decision on whether it is safe/valuable to release it or not. In the case of an increment that is un-safe, the team course corrects and comes back with an increment the next sprint that is hopefully safe or more-safe. These safe to fail experiments can be repeated over and over again until it’s time to release the increment.
Applying Kanban Correctly
Having said all of the above, there IS a time and place for Kanban — a correct context, if you will. If you’ve been reading closely, that context is as a change management process, which is ‘complicated’ work, and requires that there be already existing processes in place. So, if your software team is doing XP, Scrum, Crystal, Waterfall, RUP, DSDM, FDD, etc, then you can layer Kanban on top of it to help find bottlenecks and waste. Also, for all of those teams out there that don’t use a software development process(framework, approach, etc) that is named in the industry, you’re probably doing cowboy coding, ad-hoc, or command and control project management — none of which is a software development process either. So, layering Kanban on top of crap will still yield crap.
For those that want to apply Kanban at the enterprise level to monitor the flow of work through their Scrum teams (Or XP, Crystal, etc), or want to use it for IT support or Dev Ops, I say have at it and I hope it helps you. I imagine just visualizing your workflow alone will help in those contexts. I myself have recommended and coached Kanban for a couple of teams — but only because those teams exhibited the right context for Kanban to be successful.
Having said all of this, just visualizing your workflow and the other Kanban principles is not enough for software development. Software development has things like business value, technical complexity, and user experience/acceptance/adoption — all of which are not addressed directly by Kanban. Scrum does address these areas, as I have shown above. But hey, let’s not forget, the Kanban Method is “not a way of making software or running projects that make software.” Would you criticize a hammer for not doing a good job of being able to insert a screw into a wall?