Deep Dive into `mithril-aggregator`: Core Responsibilities, HTTP Boundaries, and Certificate/Artifact Production

Why I Studied mithril-aggregator After reading the Mithril client modules and contributing small fixes, I realized that the aggregator is the center of the whole Mithril system. The signer produces individual signatures, and the client verifies certificates and consumes artifacts, but the aggregator is where everything converges: it coordinates signers, collects signatures, produces Mithril certificates, and serves certified artifacts through HTTP endpoints. From an engineering perspective, the aggregator is a great module to study because it contains many real-world infrastructure concerns: state machines, persistence, API boundaries, resource limits, and the “correctness glue” that ensures protocol outputs are verifiable. This post summarizes what I learned about the aggregator’s role, its internal structure, and the practical points where reliability and security matters the most. What the Aggregator Does (High-level Responsibility) The aggregator’s job can be summarized in one sent