C4 Container

# 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

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:

```mermaid

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:

```yaml

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"

- "