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:

●[Component Name]: [Description]

●Documentation: [c4-component-name.md](./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

c4-container

Documentation