C4 Architecture

C4 Architecture Modelling with Structurizr DSL

Generate C4 architecture models using the Structurizr DSL and optionally render them as images.

When To Use

• User wants to analyse and document software architecture
• User asks for C4 diagrams (System Context, Container, Component, Deployment)
• User wants to generate or update a Structurizr DSL workspace file
• User wants to render architecture diagrams as images

Architecture Analysis Process

Step 1: Discover the System

Analyse the codebase to identify architectural elements:

Configuration & Build Files

• package.json, pom.xml, build.gradle, go.mod, Cargo.toml, requirements.txt
• docker-compose.yml, Dockerfile, kubernetes/*.yml
• .env, configuration files, infrastructure-as-code

Identify Elements

• People/Actors: Who uses the system? (end users, admins, external services)
• Software Systems: The system being modelled + external systems it interacts with
• Containers: Deployable units (web apps, APIs, databases, message queues, file stores)
• Components: Logical groupings within containers (controllers, services, repositories)

Map Relationships

• API calls between services (REST, gRPC, GraphQL)
• Database connections and which containers access which stores
• Message queue producers/consumers
• External integrations (payment providers, email services, auth providers)
• User interactions with the system

Step 2: Generate the Structurizr DSL

Write a workspace.dsl file following the Structurizr DSL syntax.

For the full DSL language reference, read: references/structurizr-dsl-reference.md For a working example, read: examples/example-workspace.dsl

Structure the workspace as follows:

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workspace "[System Name]" "[Brief description]" {
    model {
        // 1. Define people (actors)
        // 2. Define software systems
        //    - Nest containers inside the primary system
        //    - Nest components inside containers (if needed)
        // 3. Define relationships between elements
    }
    views {
        // 4. Create views at each required C4 level
        // 5. Apply styling via themes or element/relationship styles
    }
}

Naming Conventions:

• Use camelCase for identifiers: webApp, apiGateway, userDb
• Use descriptive display names: "Web Application", "API Gateway"
• Include technology labels: "Spring Boot REST API", "PostgreSQL 15"

Relationship Guidelines:

• Always include a description: user -> webApp "Browses products using" "HTTPS"
• Include technology where relevant: "REST/JSON", "JDBC", "AMQP"
• Direction matters: source -> destination (who initiates the interaction)

Step 3: Create Views

Generate appropriate views based on the level of detail needed:

• System Landscape: Overview of all systems (systemLandscape)
• System Context: One system + its direct interactions (systemContext)
• Container: Internal structure of a system (container)
• Component: Internal structure of a container (component)
• Deployment: Infrastructure mapping (deployment)

Always use autoLayout unless the user provides explicit layout preferences.

Step 4: Apply Styling

Use tags and styles to make diagrams readable:

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styles {
    element "Person" {
        shape Person
        background #08427B
        color #ffffff
    }
    element "Software System" {
        background #1168BD
        color #ffffff
    }
    element "Container" {
        background #438DD5
        color #ffffff
    }
    element "Component" {
        background #85BBF0
        color #000000
    }
    element "Database" {
        shape Cylinder
    }
    element "External" {
        background #999999
        color #ffffff
    }
}

Step 5: Export and Render Diagrams

All export and rendering is done via Docker. Requires Docker to be installed and running.

Export DSL to C4-PlantUML:

bashCopy code
mkdir -p ./diagrams
docker run --rm -v $PWD:/usr/local/structurizr structurizr/structurizr \
    export -workspace /usr/local/structurizr/workspace.dsl -format plantuml/c4plantuml -output /usr/local/structurizr/diagrams

Render PlantUML to PNG:

bashCopy code
docker run --rm -v $PWD/diagrams:/data plantuml/plantuml -tpng /data/*.puml

Render PlantUML to SVG:

bashCopy code
docker run --rm -v $PWD/diagrams:/data plantuml/plantuml -tsvg /data/*.puml

Other supported export formats: plantuml, mermaid, json.

Prerequisite: Docker (docker pull structurizr/structurizr && docker pull plantuml/plantuml)

Quality Checklist

Before presenting the workspace to the user, verify:

• All identified systems, containers, and components are modelled
• Every element has a description and technology label where appropriate
• Relationships have meaningful descriptions (not just "uses")
• External systems are clearly distinguished (tagged as "External")
• Database elements use the Cylinder shape
• Views exist for each appropriate C4 level
• autoLayout is applied to all views
• Styling is consistent and follows C4 colour conventions