Promise Theory—What Is It?

Configuration Management

The way we view the world in Promise Theory is as a collection of agents or nested containers of things that can keep promises. These containers could be:

  • A part of a file.

  • A file.

  • A directory (of files).

  • A partition (of directories).

  • A container (or logical partition).

  • A virtual machine (or logical machine).

  • A local area network (of machines), etc.

The reference software with this kind of thinking is still CFEngine (version 3), as it was designed explicitly in this model, though several software systems work in an implicitly promise-oriented fashion. Promise thinking permeates the world of networking too, where autonomy is built into the modus operandi of the devices. Other examples where promises are made to users include interfaces and APIs, microservices or Service Oriented Architecture (SOA).

Knowledge-Oriented Service Design

Promises turn design and configuration into a form of knowledge management, by shifting the attention away from what changes (or which algorithms to enact), onto what interfaces exist between components and what promises they keep and why. The service-oriented style of programming, made famous by Amazon and Netflix, uses this approach for scalability (not only machine scalability but for scaling human ownership). It is hailed as a cloud-friendly approach to designing systems, but Promise Theory also tells us that it is the route to very large scale. Applications have to be extensible by cooperation (sometimes called horizontal scaling through parallelism rather than vertical scaling through brute force). Databases like Cassandra illustrate how to deal with the issues of scale, redundancy and relativity.

Perhaps interestingly, biology has selected redundant services as its model for scaling tissue-based organisms. This offers a strong clue that we are on the right track. Avoiding strong dependencies is a way to avoid bottlenecks, so this shows the route to scalability.

Autonomy and standalone thinking seem to fly in the face of what we normally learn about programming—that is, to share resources, but this is not necessarily true. Security and scalability both thrive under autonomy, and complexity melts away when the dependencies between parts are removed and all control is from within. The near future world of mobile and embedded devices will not tolerate a remote-control model of management, and the sprawl of the cloud's server back end will force us to decentralize 3-D-printed micro-data centers, like the electricity substations of today. In this world, I think we can expect to see more of the autonomous thinking pervading society.


Mark Burgess is the founder, CTO and original author of CFEngine.