# Architecture Overview

## Infrastructure Architecture

```
Internet
   ↓
Load Balancer (External IP)
   ↓
Ingress Controller
   ↓
TLS Termination (Wildcard Certificate)
   ↓
┌─────────────────────────────────────────────────────┐
│         Gateway Ingress                             │
│  (*.domain.com / domain.com)                        │
└─────────────────────────────────────────────────────┘
   ↓
┌─────────────────────────────────────────────────────┐
│      Gateway Service (ClusterIP)                    │
│   gateway-service (Internal IP)                     │
│   Ports: 80 (→9080), 443 (→9443)                   │
└─────────────────────────────────────────────────────┘
   ↓
┌─────────────────────────────────────────────────────┐
│         Gateway Pods (Multiple Replicas)            │
│   - gateway-pod-1                                   │
│   - gateway-pod-2                                   │
│   - gateway-pod-3                                   │
└─────────────────────────────────────────────────────┘
   ↓
[Route Matching & Service Discovery]
   ↓
┌──────────────────┬──────────────────┐
│  Backend         │  Backend         │
│  Services        │  Services        │
│  (ClusterIP)     │  (ClusterIP)     │
└──────────────────┴──────────────────┘
   ↓
Application Pods
```

## Component Details

### 1. External Access Layer

**Load Balancer**
- Provides external IP address
- Supports LoadBalancer service type
- Exposes Ingress Controller to the internet

**Ingress Controller**
- Handles HTTP/HTTPS traffic
- TLS termination point
- Routes to appropriate backend services

### 2. Control Plane

**Deployment Method**: Helm Chart
**Namespace**: Dedicated namespace for gateway components

#### Components

**Dashboard**
- **Function**: Web UI for gateway management
- **Service Type**: ClusterIP
- **Ports**: Management ports (HTTP/HTTPS)
- **Replicas**: Configurable

**Developer Portal**
- **Function**: API documentation and developer access
- **Service Type**: ClusterIP
- **Ports**: Web service port
- **Replicas**: Configurable

**Data Plane Manager**
- **Function**: Data Plane management and configuration distribution
- **Service Type**: ClusterIP
- **Ports**: Management and proxy ports
- **Replicas**: Configurable

**PostgreSQL Database**
- **Function**: Configuration and metadata storage
- **Service Type**: ClusterIP
- **Port**: 5432/TCP
- **Storage**: Persistent volume with configurable size
- **Deployment**: StatefulSet for data persistence

**Prometheus Server**
- **Function**: Metrics collection and monitoring
- **Service Type**: ClusterIP
- **Port**: 9090/TCP
- **Storage**: Persistent volume for metrics retention

### 3. Gateway Data Plane

**Deployment Method**: Helm Chart
**High Availability**: Multiple replicas for fault tolerance

#### Gateway Deployment

- **Replicas**: Configurable (recommended: 3+)
- **Strategy**: RollingUpdate for zero-downtime deployments
- **Max Unavailable**: 25% during updates

**Gateway Groups**:
- Logical grouping of gateway instances
- Environment-based separation (dev/staging/prod)
- Independent configuration per group

#### Gateway Service

- **Type**: ClusterIP for internal routing
- **Ports**:
  - HTTP: 80/TCP → 9080/TCP
  - HTTPS: 443/TCP → 9443/TCP

#### Gateway Configuration

**Configuration Store**:
- **Connection**: Secure connection to control plane
- **TLS**: Mutual authentication enabled
- **Certificates**: Managed via Kubernetes secrets

**Configuration Volumes**:
- Gateway configuration via ConfigMap
- TLS certificates for secure communication
- Service discovery configuration

### 4. Ingress Configuration

**Gateway Ingress Resource**

```yaml
Hosts:
  - *.domain.com
  - domain.com

Backend:
  Service: gateway-service
  Port: 80

TLS:
  - hosts:
      - *.domain.com
      - domain.com
    secretName: wildcard-tls-secret
```

**Access Points**:
- External IP: Provided by Load Balancer
- Protocols: HTTP (80), HTTPS (443)
- Ingress Class: Configurable

### 5. Storage Architecture

**Persistent Volumes**:

| Component | Recommended Size | Usage |
|-----------|-----------------|-------|
| PostgreSQL Database | 10Gi+ | Configuration and metadata storage |
| Prometheus Metrics | 100Gi+ | Time-series metrics retention |
| Configuration Store | 8Gi per node | Distributed configuration (if using etcd) |

**Storage Classes**:
- Distributed storage for database persistence
- Local or network storage for metrics
- High-performance storage for configuration

## Network Flow

### External Request Flow

1. **Client Request** → Domain URL (HTTP/HTTPS)
2. **DNS Resolution** → External Load Balancer IP
3. **Ingress Controller** → TLS termination with wildcard certificate
4. **Ingress Routing** → Gateway service endpoint
5. **Gateway Service** → Load balances across gateway pod replicas
6. **Route Matching** → Gateway evaluates routes based on host/path/priority
7. **Service Discovery** → Gateway fetches backend endpoints from Kubernetes
8. **Backend Request** → Proxies to backend service pods
9. **Response** → Returns through the chain to client

### Control Plane Communication

1. **Dashboard** → Database (configuration storage)
2. **Dashboard** → Data Plane Manager (gateway group management)
3. **Data Plane Manager** → Configuration store (configuration distribution)
4. **Gateway Pods** → Control plane endpoint (fetch routes/services)
5. **Prometheus** → Gateway Pods (scrape metrics)

## Security Architecture

### TLS/SSL Configuration

**External TLS** (Ingress Layer):
- **Certificate**: Wildcard certificate (Let's Encrypt or commercial)
- **Secret**: Kubernetes TLS secret
- **Domains**: Wildcard and root domain support

**Internal TLS** (Control Plane):
- **Dashboard**: Secure HTTPS access
- **Developer Portal**: Encrypted portal access
- **Data Plane Manager**: Secure management interface

**Gateway Communication TLS**:
- **Mutual TLS**: Enabled for secure communication
- **CA Certificate**: Certificate authority validation
- **Client Certificates**: Individual component authentication

### Service Accounts & RBAC

**Gateway Service Account**: Dedicated service account per namespace

**Required Permissions**:
- `list/watch` endpoints (for service discovery)
- Read access to services and pods
- Typically bound to appropriate ClusterRole

## High Availability

### Gateway Layer
- **Multiple replicas** for fault tolerance (3+ recommended)
- **RollingUpdate** strategy for zero-downtime deployments
- **Load balancing** across all healthy instances

### Control Plane
- **Database**: StatefulSet with persistent storage
- **Monitoring**: Persistent metrics storage
- **Management Components**: Stateless, scalable replicas

### Storage
- **Database**: Distributed or replicated storage
- **Metrics**: Persistent volume with retention policy
- **Configuration**: Highly available storage backend

## Monitoring & Observability

**Metrics Collection**:
- Time-series metrics from all gateway pods
- Persistent storage for historical data
- Query interface for metrics analysis

**Gateway Metrics**:
- HTTP request rates and throughput
- Latency percentiles (p50, p95, p99)
- Error rates and status codes
- Active connections and concurrency
- Upstream service health status

**Health Checks**:
- Gateway readiness and liveness probes
- Service health endpoints
- Automated recovery mechanisms

## Scalability Considerations

**Horizontal Scaling**:
- Gateway pods: Scale based on traffic patterns
- Backend services: Auto-scaling based on metrics
- Control plane: Scale management components as needed

**Vertical Scaling**:
- Database: Expand storage as data grows
- Metrics storage: Adjust retention and volume size
- Gateway resources: Tune CPU/memory for performance

## Configuration Management

**Gateway Configuration**:
- **Source**: Dashboard UI or CLI tools
- **Storage**: Centralized database
- **Distribution**: Control plane to data plane synchronization
- **Format**: YAML configuration or Web-based management

**Kubernetes Resources**:
- **Deployment**: Helm charts for standardized installation
- **Management**: Kubernetes-native resource management
- **Namespaces**: Logical separation of environments

---

*This architecture provides enterprise-grade API Gateway capabilities with high availability, scalability, and comprehensive monitoring.*