For those who saw Andy Carmichael's "Shortest Possible Definition of Kanban" talk at Lean Kanban United Kingdom, you will know that he talked about Kanban as having two approaches to scaling: scaling by not scaling through a service-oriented approach and scaling through a scale free assumption. This blog post addresses how that latter assumption is true. Our clarity on this on trult emerged during our Lean Kanban Inc leadership retreat in Phoenix recently where Mike Burrows and I agreed the symmetry of how Kanban scales. It turns out to be remarkably simple. Simplicity is a good thing. We are all for maintaining simplicity and leveraging its powerful nature with respect to complex domain problems.
You scale Kanban by limiting formerly infinite buffers between services.
1. Proto-Kanban to Kanban System
On this proto-Kanban board, the activity columns are isolated by infinite limits on the "done" states, meaning that there is pull system and WIP in the whole system is not limited. This matures into a full kanban system by limiting the "done" column WIP. Every time we limit a formerly infinite queue, we couple more of the system together.
2. Kanban System to Organization Scale System of Kanban Systems
Typically, dependencies between kanban systems are visualized by creating a buffer for the dependent work items. Items waiting on service from a dependent system are usually buffered in an infinite buffer. As the organization matures and develops the use of an Operations Review feedback loop, it should be possible to adjust capacity allocation in dependent systems to insure a predictable response. Service level agreements between depedent systems should emerge. With predictability of response from a dependent system, it should be possible to introduce a WIP limit on the buffer of dependent work items. Limiting the size of the buffer couples the formerly independent systems together. The net effect is to make the larger system of systems more predictable and ultimately to improve the service delivery for customers (and other external stakeholders).
Kanban scales in a scale free manner as through the mechanism of limiting work-in-progress wherever it is found and particularly in buffers that decouple services.