# WebAssembly Runtime Architecture
## Overview
The Caxton WebAssembly Runtime provides a secure, isolated execution environment for multi-agent systems. Each agent runs in its own sandboxed WASM instance with enforced resource limits and security policies.
## Key Components
### 1. WasmRuntime
The main orchestrator that manages the lifecycle of all agents in the system.
**Responsibilities:**
- Agent deployment and lifecycle management
- Resource allocation and enforcement
- Security policy enforcement
- Message routing between agents
### 2. Sandbox
Each agent runs in an isolated sandbox that prevents interference with other agents or the host system.
**Features:**
- Complete memory isolation
- CPU fuel-based scheduling
- Controlled host function access
- Resource limit enforcement
### 3. Security Policy
Configurable security policies control what WASM features and host functions are available.
**Security Levels:**
- **Strict**: Minimal permissions, no advanced WASM features
- **Default**: Balanced security with essential features
- **Relaxed**: More permissive for trusted environments
### 4. Resource Manager
Enforces resource limits to prevent any single agent from consuming excessive resources.
**Managed Resources:**
- Memory (per-agent limit)
- CPU fuel (computation units)
- Execution time
- Message size
## Architecture Diagram
```
┌─────────────────────────────────────────────────────────┐
│ Caxton Runtime │
├─────────────────────────────────────────────────────────┤
│ │
│ ┌──────────────┐ ┌──────────────┐ ┌──────────────┐ │
│ │ Agent 1 │ │ Agent 2 │ │ Agent 3 │ │
│ │ (Sandbox) │ │ (Sandbox) │ │ (Sandbox) │ │
│ └──────────────┘ └──────────────┘ └──────────────┘ │
│ ▲ ▲ ▲ │
│ │ │ │ │
│ ┌──────┴─────────────────┴─────────────────┴────────┐ │
│ │ Resource Manager │ │
│ │ • Memory limits │ │
│ │ • CPU fuel tracking │ │
│ │ • Execution timeouts │ │
│ └────────────────────────────────────────────────────┘ │
│ │
│ ┌────────────────────────────────────────────────────┐ │
│ │ Security Policy │ │
│ │ • WASM feature gates │ │
│ │ • Host function permissions │ │
│ │ • Sandboxing rules │ │
│ └────────────────────────────────────────────────────┘ │
│ │
│ ┌────────────────────────────────────────────────────┐ │
│ │ Host Functions │ │
│ │ • log() │ │
│ │ • get_time() │ │
│ │ • send_message() │ │
│ └────────────────────────────────────────────────────┘ │
└─────────────────────────────────────────────────────────┘
```
## Agent Lifecycle
```
Unloaded
│
▼
Deploy (validate WASM module)
│
▼
Loaded
│
▼
Start (initialize sandbox)
│
▼
Running ◄─────┐
│ │
▼ │
Execute │
Functions ────┘
│
▼
Draining (graceful shutdown)
│
▼
Stopped
```
## Security Features
### 1. WASM Feature Restrictions
- **SIMD**: Disabled by default (prevents certain attack vectors)
- **Reference Types**: Disabled (reduces complexity)
- **Bulk Memory**: Disabled (prevents rapid memory operations)
- **Threads**: Disabled (simplifies isolation)
### 2. Fuel-Based Scheduling
- Each agent has a fuel budget for CPU operations
- Prevents infinite loops and resource hogging
- Enables cooperative multitasking
### 3. Memory Isolation
- Each sandbox has its own memory space
- No shared memory between agents
- Enforced memory limits per agent
### 4. Controlled Host Access
- Limited set of host functions exposed
- No direct filesystem access
- No raw network socket access
- Message-based communication only
## Resource Limits
### Default Limits
- **Memory**: 10MB per agent
- **CPU Fuel**: 1,000,000 units
- **Execution Time**: 5 seconds
- **Message Size**: 100KB
### Customization
Resource limits can be customized per deployment:
```rust
let config = WasmRuntimeConfig {
resource_limits: ResourceLimits {
max_memory_bytes: 5 * 1024 * 1024, // 5MB
max_cpu_fuel: 500_000,
max_execution_time: Duration::from_secs(2),
max_message_size: 50 * 1024, // 50KB
},
..Default::default()
};
```
## Performance Characteristics
### Startup Time
- Target: < 100ms per agent
- Achieved through:
- Pre-compiled WASM caching
- Lazy initialization
- Minimal bootstrap overhead
### Throughput
- Supports 100+ concurrent agents
- Message passing overhead < 1ms
- Context switching via fuel metering
### Memory Efficiency
- Base overhead: ~1MB per sandbox
- Shared engine reduces duplication
- Automatic cleanup on agent removal
## Error Handling
### Resource Exhaustion
- Graceful degradation when limits reached
- Clear error messages for debugging
- Automatic resource cleanup
### Security Violations
- Immediate termination of violating agents
- Audit logging of violations
- No impact on other agents
### Recovery Mechanisms
- Automatic restart capabilities
- State checkpointing (future feature)
- Circuit breaker patterns
## Integration Points
### Management API
- gRPC and REST interfaces
- Agent deployment and control
- Monitoring and metrics
### Observability
- OpenTelemetry integration
- Structured logging
- Performance metrics
- Distributed tracing
### External Tools (via MCP)
- Controlled access to external resources
- Permission-based tool access
- Audit trail of tool usage
## Best Practices
### 1. Agent Design
- Keep agents small and focused
- Use message passing for communication
- Handle resource limits gracefully
### 2. Security
- Use strict policy for untrusted agents
- Regularly audit host function usage
- Monitor resource consumption
### 3. Performance
- Pre-warm agent pools for low latency
- Batch message processing
- Use appropriate resource limits
### 4. Operations
- Monitor agent health
- Set up alerts for resource exhaustion
- Regular security audits
## Future Enhancements
### Planned Features
- WebAssembly Component Model support
- Advanced scheduling algorithms
- State persistence and recovery
- Cross-instance agent migration
- Dynamic resource adjustment
### Research Areas
- Zero-copy message passing
- WASM JIT optimization
- Distributed agent coordination
- Machine learning-based resource prediction