How do you implement a service mesh pattern in Node.js?

Question

Accepted Answer

**Service mesh** — infrastructure layer for service-to-service communication.

**Key components:**
- 1. **Sidecar proxy** — handles network concerns.
- 2. **Service discovery** — find other services.
- 3. **Load balancing** — distribute traffic.
- 4. **Observability** — metrics, tracing.

```javascript
// Simple service discovery
class ServiceRegistry {
    constructor() {
        this.services = new Map();
    }

register(name, instance) {
        if (!this.services.has(name)) {
            this.services.set(name, []);
        }
        this.services.get(name).push({
            ...instance,
            lastHeartbeat: Date.now(),
        });
    }

discover(name) {
        const instances = this.services.get(name) || [];
        const healthy = instances.filter(
            i => Date.now() - i.lastHeartbeat < 10000
        );
        // Round-robin
        return healthy[Math.floor(Math.random() * healthy.length)];
    }

deregister(name, instanceId) {
        const instances = this.services.get(name) || [];
        this.services.set(name,
            instances.filter(i => i.id !== instanceId)
        );
    }
}

// Client-side load balancing
async function callService(serviceName) {
    const instance = registry.discover(serviceName);
    if (!instance) throw new Error("No healthy instances");
    return fetch(`http://${instance.host}:${instance.port}`);
}
```

**Production tools:** Istio, Linkerd, Consul.

Node.js: How do you implement a service mesh pattern in Node.js?