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feat: resource capsule implementation
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‎DESIGN.md‎

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# DESIGN.md
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## Resource Capsules Design Proposal
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### Overview
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Resource Capsules are a novel approach to resource sharing in containerized environments. Unlike traditional methods such as volumes or bind mounts, Resource Capsules are self-contained, versioned, and isolated resource units that can be dynamically attached to containers.
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### Explanation of Design Points
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#### Overview
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Resource Capsules address the limitations of traditional resource-sharing methods by introducing versioning, dynamic attachment, and isolation. This ensures that containers can access specific versions of resources securely and efficiently.
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#### Key Features
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1. **Versioning**: Ensures that containers can use specific versions of resources, reducing compatibility issues and enabling reproducibility.
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2. **Dynamic Attachment**: Allows resources to be attached or detached from running containers without requiring a restart, improving flexibility.
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3. **Isolation**: Prevents resource conflicts and enhances security by isolating capsules from the host system and other containers.
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#### Components
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1. **Capsule Store**:
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- Acts as a centralized repository for storing and managing capsules.
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- Capsules are stored in a compressed and immutable format to ensure integrity.
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2. **Capsule Manager**:
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- Handles the creation, retrieval, and attachment of capsules.
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- Ensures that capsules are properly managed throughout their lifecycle.
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3. **Capsule API**:
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- Provides a user-friendly interface for interacting with capsules.
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- Simplifies the process of creating, updating, and managing capsules.
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### Workflow
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1. **Create Capsule**: Developers can create capsules containing specific resources, such as libraries or configurations.
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```bash
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capsule create --name libssl --version 1.1.1 --path /usr/lib/libssl.so
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```
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2. **Store Capsule**: Capsules are stored in the Capsule Store for easy retrieval.
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3. **Request Capsule**: Containers can request specific capsules at runtime, ensuring they have access to the required resources.
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```bash
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basic-docker run --capsule libssl:1.1.1 /bin/myapp
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```
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4. **Attach Capsule**: The Capsule Manager dynamically attaches the requested capsule to the container, making it available for use.
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### Benefits
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- **Flexibility**: Capsules can be shared across multiple containers without modifying the host system.
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- **Security**: Isolated capsules reduce the risk of resource conflicts and vulnerabilities.
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- **Efficiency**: Capsules are reusable, reducing duplication and storage overhead.
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### Implementation Details
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- **CapsuleManager**: A Go struct that manages the lifecycle of capsules, ensuring they are created, retrieved, and attached correctly.
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- **AttachCapsule**: A method that dynamically attaches capsules to containers, enabling runtime flexibility.
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- **Test Cases**: Comprehensive unit tests validate the functionality of the CapsuleManager and ensure reliability.
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### Future Enhancements
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- **Capsule Dependency Resolution**: Automatically resolve dependencies between capsules to simplify management.
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- **Garbage Collection**: Implement a mechanism to clean up unused capsules, optimizing storage.
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- **Remote Management**: Extend the Capsule API to support remote management, enabling capsules to be accessed and managed across distributed systems.
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### Design Diagrams
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#### Resource Capsules Architecture
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```mermaid
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flowchart TD
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subgraph CapsuleSystem
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CapsuleManager["Capsule Manager"]
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CapsuleStore["Capsule Store"]
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CapsuleAPI["Capsule API"]
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end
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subgraph ContainerRuntime
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Container["Container"]
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end
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CapsuleManager -->|Manages| CapsuleStore
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CapsuleAPI -->|Interacts| CapsuleManager
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CapsuleManager -->|Attaches| Container
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CapsuleStore -->|Provides| Container
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```
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#### Capsule Workflow
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```mermaid
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sequenceDiagram
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participant Developer
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participant CapsuleAPI
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participant CapsuleManager
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participant Container
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Developer->>CapsuleAPI: Create Capsule
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CapsuleAPI->>CapsuleManager: Store Capsule
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Developer->>CapsuleAPI: Request Capsule
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CapsuleAPI->>CapsuleManager: Retrieve Capsule
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CapsuleManager->>Container: Attach Capsule
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```
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#### Capsule Lifecycle
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```mermaid
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graph TD
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A[Create Capsule] --> B[Store Capsule]
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B --> C[Attach Capsule]
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C --> D[Detach Capsule]
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D --> E[Delete Capsule]
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```
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These diagrams provide a visual representation of the Resource Capsules architecture, workflow, and lifecycle.
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### Textual Diagrams and Code Snippets
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#### Resource Capsules Architecture (Textual Diagram)
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```
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Capsule System:
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- Capsule Manager: Manages the lifecycle of capsules.
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- Capsule Store: Stores capsules in a compressed, immutable format.
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- Capsule API: Provides an interface for capsule operations.
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Container Runtime:
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- Container: Requests and uses capsules.
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Relationships:
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- Capsule Manager -> Capsule Store: Manages capsules.
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- Capsule API -> Capsule Manager: Interacts with the manager.
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- Capsule Manager -> Container: Attaches capsules to containers.
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```
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#### Capsule Workflow (Textual Diagram)
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```
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Developer -> Capsule API: Create Capsule
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Capsule API -> Capsule Manager: Store Capsule
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Developer -> Capsule API: Request Capsule
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Capsule API -> Capsule Manager: Retrieve Capsule
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Capsule Manager -> Container: Attach Capsule
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```
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#### Capsule Lifecycle (Textual Diagram)
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```
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Create Capsule -> Store Capsule -> Attach Capsule -> Detach Capsule -> Delete Capsule
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```
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#### Code Snippets
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**Capsule Creation**
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```go
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cm := NewCapsuleManager()
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cm.AddCapsule("libssl", "1.1.1", "/usr/lib/libssl.so")
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```
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**Capsule Retrieval**
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```go
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capsule, exists := cm.GetCapsule("libssl", "1.1.1")
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if !exists {
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fmt.Println("Capsule not found")
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}
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```
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**Capsule Attachment**
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```go
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err := cm.AttachCapsule("container-1234", "libssl", "1.1.1")
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if err != nil {
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fmt.Printf("Failed to attach capsule: %v\n", err)
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}
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```
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These textual diagrams and code snippets provide a clear and concise representation of the Resource Capsules feature.

‎README.md‎

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@j143 ➜ /workspaces/basic-docker-engine (main) $ ./basic-docker
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Environment detected: inContainer=true, hasNamespacePrivileges=true, hasCgroupAccess=false
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Usage:
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lean-docker run <command> [args...] - Run a command in a container
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lean-docker ps - List running containers
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lean-docker images - List available images
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lean-docker info - Show system information
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basic-docker run <command> [args...] - Run a command in a container
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basic-docker ps - List running containers
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basic-docker images - List available images
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basic-docker info - Show system information
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```
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### create necessary folders
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==== Testing with busybox ====
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Environment detected: inContainer=true, hasNamespacePrivileges=true, hasCgroupAccess=true
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Starting container container-1743307590
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Error: failed to create symlink for sh: symlink busybox /tmp/lean-docker/containers/container-1743307590/rootfs/bin/sh: file exists
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Error: failed to create symlink for sh: symlink busybox /tmp/basic-docker/containers/container-1743307590/rootfs/bin/sh: file exists
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==== Skipping isolation tests (needs root) ====
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==== All tests completed ====
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```
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```
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## Test Strategy
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### Current Testing Status
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```mermaid
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graph TD
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A[Unit Tests] --> B[Integration Tests]
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B --> C[End-to-End Tests]
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C --> D[Verification Script]
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%% Styling
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classDef process fill:#ffe0d0,stroke:#ff8030,stroke-width:2px
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class A,B,C,D process
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```
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- **Unit Tests**: Present in `main_test.go` and `image_test.go`.
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- **Integration Tests**: Covered partially in `verify.sh`.
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- **End-to-End Tests**: Basic functionality tested via `verify.sh`.
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- **Verification Script**: `verify.sh` runs additional checks and validations.

‎adr-001-resource-capsules.md‎

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# Architectural Decision Record (ADR)
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## ADR-001: Resource Capsules
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### Context
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In containerized environments, resource sharing is typically achieved through volumes or bind mounts. However, these methods lack versioning, dynamic attachment capabilities, and isolation, which are critical for modern containerized applications.
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### Decision
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We decided to implement **Resource Capsules**, a novel approach to resource sharing that provides versioning, dynamic attachment, and isolation. This decision aligns with the goals of enhancing flexibility, security, and efficiency in resource management.
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### Consequences
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#### Positive
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- **Versioning**: Enables containers to use specific versions of shared resources.
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- **Dynamic Attachment**: Allows capsules to be attached or detached from running containers without restarting them.
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- **Isolation**: Ensures resources are secure and consistent across containers.
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- **Reusability**: Capsules can be reused across multiple containers, reducing duplication.
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#### Negative
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- **Complexity**: Adds additional components like Capsule Manager and Capsule Store.
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- **Overhead**: Requires managing capsule lifecycle and storage.
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### Alternatives Considered
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1. **Traditional Volumes**:
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- Pros: Simple and widely used.
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- Cons: No versioning or dynamic attachment capabilities.
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2. **Bind Mounts**:
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- Pros: Direct access to host resources.
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- Cons: Security risks and lack of isolation.
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### Status
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Accepted and implemented in the `resource-capsules` branch.
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### Design Diagram
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#### Resource Capsules Decision Flow
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```mermaid
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graph TD
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A[Identify Resource Sharing Needs] --> B[Evaluate Existing Methods]
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B -->|Lack Versioning| C[Consider Resource Capsules]
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C --> D[Design Capsule System]
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D --> E[Implement Capsule Manager]
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E --> F[Integrate with Container Runtime]
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F --> G[Validate and Test]
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G --> H[Deploy Resource Capsules]
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```
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This diagram illustrates the decision-making process for adopting Resource Capsules.
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### Writing Best Practices
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- **Clarity**: Use simple and direct language to explain the decision.
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- **Conciseness**: Avoid unnecessary details; focus on the key points.
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- **Structure**: Organize the document into clear sections with headings.
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- **Consistency**: Use consistent terminology and formatting throughout the document.
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### Future Work
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- Extend Capsule API for remote management.
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- Implement garbage collection for unused capsules.
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- Add support for capsule dependency resolution.

‎main.go‎

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AppLayerPath string
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}
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// ResourceCapsule represents a self-contained, versioned resource unit.
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type ResourceCapsule struct {
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Name string
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Version string
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Path string
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}
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// CapsuleManager handles the lifecycle of Resource Capsules.
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type CapsuleManager struct {
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Capsules map[string]ResourceCapsule
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}
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// NewCapsuleManager initializes a new CapsuleManager.
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func NewCapsuleManager() *CapsuleManager {
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return &CapsuleManager{
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Capsules: make(map[string]ResourceCapsule),
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}
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}
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// AddCapsule adds a new Resource Capsule to the manager.
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func (cm *CapsuleManager) AddCapsule(name, version, path string) {
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key := name + ":" + version
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cm.Capsules[key] = ResourceCapsule{Name: name, Version: version, Path: path}
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}
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// GetCapsule retrieves a Resource Capsule by name and version.
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func (cm *CapsuleManager) GetCapsule(name, version string) (ResourceCapsule, bool) {
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key := name + ":" + version
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capsule, exists := cm.Capsules[key]
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return capsule, exists
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}
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// AttachCapsule attaches a capsule to a container.
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func (cm *CapsuleManager) AttachCapsule(containerID, name, version string) error {
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key := name + ":" + version
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_, exists := cm.Capsules[key]
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if !exists {
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return fmt.Errorf("capsule %s:%s not found", name, version)
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}
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// Logic to attach the capsule to the container's filesystem.
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fmt.Printf("Attaching capsule %s:%s to container %s\n", name, version, containerID)
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return nil
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}
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// To initialize the directories
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func initDirectories() error {
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dirs := []string{

‎main_test.go‎

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if status != "Stopped" {
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t.Errorf("Expected status 'Stopped', but got '%s'", status)
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}
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}
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// TestCapsuleManager:
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// - Verifies the CapsuleManager's functionality, including adding, retrieving, and attaching Resource Capsules.
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// - Setup: Initializes a CapsuleManager instance.
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// - Expected Outcome: Capsules are added, retrieved, and attached correctly.
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func TestCapsuleManager(t *testing.T) {
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cm := NewCapsuleManager()
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// Add a capsule
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cm.AddCapsule("libssl", "1.1.1", "/usr/lib/libssl.so")
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// Retrieve the capsule
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capsule, exists := cm.GetCapsule("libssl", "1.1.1")
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if !exists {
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t.Fatalf("Expected capsule libssl:1.1.1 to exist")
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}
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if capsule.Name != "libssl" || capsule.Version != "1.1.1" || capsule.Path != "/usr/lib/libssl.so" {
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t.Errorf("Capsule data mismatch: got %+v", capsule)
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}
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// Attach the capsule to a container
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err := cm.AttachCapsule("container-1234", "libssl", "1.1.1")
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if err != nil {
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t.Errorf("Failed to attach capsule: %v", err)
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}
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// Try to attach a non-existent capsule
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err = cm.AttachCapsule("container-1234", "libcrypto", "1.0.0")
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if err == nil {
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t.Errorf("Expected error when attaching non-existent capsule, got nil")
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}
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}

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