C4 Container Level: System Deployment

Use this skill when

• •Working on c4 container level: system deployment tasks or workflows
• •Needing guidance, best practices, or checklists for c4 container level: system deployment

Do not use this skill when

• •The task is unrelated to c4 container level: system deployment
• •You need a different domain or tool outside this scope

Instructions

• •Clarify goals, constraints, and required inputs.
• •Apply relevant best practices and validate outcomes.
• •Provide actionable steps and verification.
• •If detailed examples are required, open resources/implementation-playbook.md.

Containers

[Container Name]

• •Name: [Container name]
• •Description: [Short description of container purpose and deployment]
• •Type: [Web Application, API, Database, Message Queue, etc.]
• •Technology: [Primary technologies: Node.js, Python, PostgreSQL, Redis, etc.]
• •Deployment: [Docker, Kubernetes, Cloud Service, etc.]

Purpose

[Detailed description of what this container does and how it's deployed]

Components

This container deploys the following components:

• •
  • •Documentation: c4-component-name.md

Interfaces

[API/Interface Name]

• •Protocol: [REST/GraphQL/gRPC/Events/etc.]
• •Description: [What this interface provides]
• •Specification: [Link to OpenAPI/Swagger/API Spec file]
• •Endpoints:
  • •GET /api/resource - [Description]
  • •POST /api/resource - [Description]

Dependencies

Containers Used

• •[Container Name]: [How it's used, communication protocol]

External Systems

• •[External System]: [How it's used, integration type]

Infrastructure

• •Deployment Config: [Link to Dockerfile, K8s manifest, etc.]
• •Scaling: [Horizontal/vertical scaling strategy]
• •Resources: [CPU, memory, storage requirements]

Container Diagram

Use proper Mermaid C4Container syntax:

C4Container
    title Container Diagram for [System Name]

    Person(user, "User", "Uses the system")
    System_Boundary(system, "System Name") {
        Container(webApp, "Web Application", "Spring Boot, Java", "Provides web interface")
        Container(api, "API Application", "Node.js, Express", "Provides REST API")
        ContainerDb(database, "Database", "PostgreSQL", "Stores data")
        Container_Queue(messageQueue, "Message Queue", "RabbitMQ", "Handles async messaging")
    }
    System_Ext(external, "External System", "Third-party service")

    Rel(user, webApp, "Uses", "HTTPS")
    Rel(webApp, api, "Makes API calls to", "JSON/HTTPS")
    Rel(api, database, "Reads from and writes to", "SQL")
    Rel(api, messageQueue, "Publishes messages to")
    Rel(api, external, "Uses", "API")

**Key Principles** (from [c4model.com](https://c4model.com/diagrams/container)):

- Show **high-level technology choices** (this is where technology details belong)
- Show how **responsibilities are distributed** across containers
- Include **container types**: Applications, Databases, Message Queues, File Systems, etc.
- Show **communication protocols** between containers
- Include **external systems** that containers interact with

API Specification Template

For each container API, create an OpenAPI/Swagger specification:

openapi: 3.1.0
info:
  title: [Container Name] API
  description: [API description]
  version: 1.0.0
servers:
  - url: https://api.example.com
    description: Production server
paths:
  /api/resource:
    get:
      summary: [Operation summary]
      description: [Operation description]
      parameters:
        - name: param1
          in: query
          schema:
            type: string
      responses:
        '200':
          description: [Response description]
          content:
            application/json:
              schema:
                type: object

Example Interactions

• •"Synthesize all components into containers based on deployment definitions"
• •"Map the API components to containers and document their APIs as OpenAPI specs"
• •"Create container-level documentation for the microservices architecture"
• •"Document container interfaces as Swagger/OpenAPI specifications"
• •"Analyze Kubernetes manifests and create container documentation"

Key Distinctions

• •vs C4-Component agent: Maps components to deployment units; Component agent focuses on logical grouping
• •vs C4-Context agent: Provides container-level detail; Context agent creates high-level system diagrams
• •vs C4-Code agent: Focuses on deployment architecture; Code agent documents individual code elements

Output Examples

When synthesizing containers, provide:

• •Clear container boundaries with deployment rationale
• •Descriptive container names and deployment characteristics
• •Complete API documentation with OpenAPI/Swagger specifications
• •Links to all contained components
• •Mermaid container diagrams showing deployment architecture
• •Links to deployment configurations (Dockerfiles, K8s manifests, etc.)
• •Infrastructure requirements and scaling considerations
• •Consistent documentation format across all containers

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