DDD: Domains Sized to Contain Decisions
This blog documents learnings from building Angzarr—a polyglot event sourcing framework. The framework core is written in Rust, so examples here are primarily Rust.
Angzarr doesn't require Rust. Client SDKs exist for Go, Python, Java, C#, and C++. The author—a polyglot developer—doesn't believe Rust is the best language for everything. It is the right choice for this framework's core, and building it has produced these learnings.
The Rust should be readable by most programmers. If you have questions: consult The Rust Book, ask an LLM, or email the author.
The uncomfortable truth: most DDD teams draw their bounded contexts too small.
Not too large—too small. They slice by CRUD entity, by database table, by team org chart. The result? Contexts that cannot make decisions autonomously. Every meaningful operation requires cross-context coordination. The architecture devolves into a distributed monolith with extra network hops.
This post argues for a different principle: a bounded context is correctly sized when every decision that changes its invariants can be made entirely within it, without synchronous runtime dependency on another context.