# Service Discovery, Configuration and Service Mesh — Monolith vs Microservices

Source: https://www.skillbyai.com/en/monolith-microservices/i-discovery

> Let services find each other and manage cross-cutting network concerns.

## Finding and securing many moving services

Service instances come and go as they scale and redeploy, so their addresses change. **Service discovery** solves this. In **Kubernetes**, a Service gets a stable DNS name (`checkout.shop.svc.cluster.local`) and load-balances to healthy pods; outside Kubernetes, registries such as Consul play the same role. **Configuration** should come from the environment, config maps or a configuration service, with secrets in a secret manager, never baked into images. A **service mesh** (Istio, Linkerd, Cilium service mesh) moves cross-cutting network concerns into proxies or the node network layer: **mutual TLS** between services, retries and timeouts, traffic splitting for canaries, and uniform telemetry, without changing application code. A mesh adds operational complexity and some latency, so adopt it when you have enough services and requirements, such as zero-trust mTLS everywhere, to justify it.

## Discovery through Kubernetes DNS

The client calls a stable name; Kubernetes routes to a healthy pod.

```yaml
apiVersion: v1
kind: Service
metadata:
  name: checkout
  namespace: shop
spec:
  selector:
    app: checkout
  ports:
    - port: 80
      targetPort: 8080
---
# another service's configuration
apiVersion: v1
kind: ConfigMap
metadata:
  name: orders-config
  namespace: shop
data:
  CHECKOUT_URL: http://checkout.shop.svc.cluster.local
  HTTP_TIMEOUT_MS: "800"
```

## An office directory instead of desk numbers

People change desks all the time, so you look colleagues up in the directory (service discovery) instead of memorising desk numbers. A service mesh is like the building's mailroom that checks IDs, tracks every parcel and reroutes when someone moves.

**Quiz:** What does a service mesh typically provide without application code changes?

- [ ] Database schema migrations
- [ ] Frontend rendering
- [ ] Business validation rules
- [x] Mutual TLS, retries, traffic splitting and telemetry between services

*Answer:* Mutual TLS, retries, traffic splitting and telemetry between services. Meshes handle network-level concerns uniformly through proxies or the network layer.