C4/Diagram/Dynamic

• Dynamic diagram (C4 diagram)

  • Overview

    • A supporting C4 diagram describing runtime behaviour—collaborations, message flows, call sequences—using the same structural elements (people, software systems, containers, components) as the static views.
    • Answers what happens over time** or how a use case* traverses the architecture*.

  • Context

    • The core C4 static diagrams are not sequence charts; when chronology matters, the dynamic view is the intended supplement (see C4/Diagram).

  • Key principles

    • Narrative — Anchor on a concrete scenario (“checkout”, “password reset”) rather than abstract “data flows everywhere”.
    • Scoped — Keep participant sets small; explode into multiple diagrams if needed.

  • Mechanism

    • Often rendered as numbered interactions or UML-style collaboration idioms while preserving C4 element identities.

  • Examples

    • OAuth token exchange between browser, BFF, and identity provider; async saga steps across containers.

  • Misconceptions

    • “Any arrow on a container diagram is dynamic” — Misleading; static diagrams show possible relationships—dynamic diagrams show ordered interactions for a story.
    • “Dynamic replaces integration tests” — False; it communicates intent—tests still verify it.