Developer Architecture Reference

About 719 wordsAbout 2 min

2025-01-27

This page provides a developer‑oriented view of TKA’s architecture.

It describes the components, APIs, resources, and control flows in detail.

System Components

Package Architecture

TKA follows a clean architecture with well-defined layers:

┌─────────────────────────────────────────────────────────────┐
│ CLI Layer (cmd/cli)                                         │
│ ├── HTTP client requests                                    │
│ └── Shell integration                                       │
└─────────────────────────────────────────────────────────────┘
┌─────────────────────────────────────────────────────────────┐
│ HTTP API Layer (pkg/api)                                    │
│ ├── Gin router and handlers                                 │
│ ├── Request/response models (pkg/models)                    │
│ └── Authentication middleware (pkg/middleware/auth)         │
└─────────────────────────────────────────────────────────────┘
┌─────────────────────────────────────────────────────────────┐
│ Business Logic Layer (pkg/service)                          │
│ ├── Service interface                                       │
│ ├── Operator implementation (pkg/service/operator)          │
│ └── Mock implementation (pkg/service/mock)                  │
└─────────────────────────────────────────────────────────────┘
┌─────────────────────────────────────────────────────────────┐
│ Infrastructure Layer                                        │
│ ├── Kubernetes operator (pkg/operator)                      │
│ ├── Tailscale networking (pkg/tailscale)                    │
│ └── Utility functions (pkg/utils)                           │
└─────────────────────────────────────────────────────────────┘

1. TKA CLI

Responsibilities:

Provide user‑facing commands (login, logout, shell, etc.)
Construct API requests to TKA Server
Manage kubeconfig files
Integrate with shell environments
Display session information

Command Tree:

tka
├── login          # Authenticate and get kubeconfig
├── logout         # Revoke access and cleanup
├── shell          # Start subshell with temp access
├── kubeconfig     # Fetch current kubeconfig
├── reauthenticate # Refresh credentials
├── get            # Status and information commands
│   ├── login      # Show current login status
│   └── kubeconfig # Alias for kubeconfig command
└── integration    # Generate shell integration code

Tip

Check out the full CLI Reference that is auto generated using the Cobra documentation of each command

2. TKA Server

Responsibilities:

Expose REST API over tsnet (tailnet‑only)
Authenticate users via a dedicated Gin middleware that integrates with Tailscale WhoIs. The middleware extracts the username and capability from the request context before passing control to the handlers. (See Request Flows: Tailscale Auth Middleware)
Validate ACL capabilities (role + validity period)
Delegate business logic to service layer (pkg/service)
Write TkaSignin CRDs into the Kubernetes cluster via operator service
Return kubeconfigs with ephemeral ServiceAccount tokens

Implementation:

Networking: pkg/tailscale - Tailscale-only HTTP server
HTTP: Gin router + authentication middleware (pkg/middleware/auth)
Business Logic: Service layer (pkg/service) with operator implementation
Data Models: Structured API models (pkg/models)
Kubernetes API: client-go via operator service
Observability: OpenTelemetry (traces, metrics, logs)

Deployment:

Runs as a Kubernetes Deployment
Stateless (no DB; persistence via Kubernetes API)

API Endpoints:

Authentication API (/api/v1alpha1):

POST /login → authenticate user, create TkaSignin
GET /login → check current authentication status
GET /kubeconfig → return kubeconfig for active session
POST /logout → revoke session

Orchestrator API (/orchestrator/v1alpha1):

GET /clusters → list available clusters for user
POST /clusters → register new cluster (future)

3. Middleware Layer (`pkg/middleware`)

Responsibilities:

Handle cross-cutting concerns for HTTP requests
Provide authentication and authorization
Extract user identity from Tailscale network
Validate capability rules from Tailscale ACL

Implementation:

Base Interface: middleware.Middleware - Generic middleware contract
Auth Middleware: middleware/auth.ginAuthMiddleware - Tailscale authentication
Context Helpers: middleware/auth.GetUsername(), GetCapability() - Access user data
Mock Support: middleware/auth/mock.AuthMiddleware - Testing middleware

4. Service Layer (`pkg/service`)

Responsibilities:

Abstract business logic from HTTP handlers
Provide stable interface for different implementations
Handle credential lifecycle management
Validate business rules and constraints

Implementation:

Interface: service.Service - Core business operations
Production: service/operator.Service - Kubernetes operator integration
Testing: service/mock.MockAuthService - Configurable mock for tests
Models: service.SignInInfo - Router-agnostic authentication status

5. TKA Operator (Controller)

Responsibilities:

Watch TkaSignin CRDs
Create/delete ServiceAccounts
Bind ClusterRoles/Roles via RoleBindings
Generate ServiceAccount tokens
Clean up expired resources

Implementation:

Framework: controller-runtime
Custom Resource: TkaSignin
RBAC: ServiceAccount + RoleBinding management
Metrics: exposed at /metrics/controller
Integration: Used by service/operator.Service

Reconciliation Flow:

6. TKA Orchestrator

Responsibilities:

Provide cluster discoverability to TKA
List all clusters available to a user

Implementation:

Resource Model

Custom Resource: `TkaSignin`

Represents a user session request.

Spec fields:

username: Tailscale user identity
capability: ACL capability name
ttl: requested session duration

Status fields:

phase: Pending | Active | Expired
serviceAccount: name of provisioned SA
expiry: timestamp

Resource Naming Conventions

ServiceAccount: tka-user-{sanitized-username} Example: tka-user-alice
ClusterRoleBinding: {serviceAccount}-binding Example: tka-user-alice-binding
TkaSignin: tka-user-{sanitized-username} Example: tka-user-alice