The debate on monoliths vs microservices as architectural patterns for modern software systems usually focuses on technological aspects, missing crucial details around organizational strategy and team dynamics.

Should we start with a monolith and extract microservices or start with microservices? How many microservices is the right number? These kinds of questions indicate a confusion that is made worse by the perceived need to adopt lots of new technology in order to make microservices work.

The false dichotomy between monoliths and microservices helps no-one. Instead, switched-on organizations start with the team cognitive load required to build and run a part of the software system. If a team is not able to understand fully the details of a service or subsystem, there is little chance of the team being able to own and support it.

The resulting team-sized services are by definition suitable in size and complexity for a single team to own, develop, and run. No longer do we care how many lines of code there are in a single service or whether it is a "monolith": what we care about is that a team can own and run the software effectively.

Using team cognitive load as the guiding principle - assessed by the team via measures such as supportability, deployability, testability, operability, prioritization difficulties and domain complexity - organizations can optimize for sustainable ownership and evolution of software systems.

This talk draws on research and case studies from the book Team Topologies by Matthew Skelton and Manuel Pais (IT Revolution Press, 2019) together with first-hand consulting experience from the authors with organizations around the world.