L04 — Services & Networking

Pods are ephemeral and get random IPs. Networking in Kubernetes is the layer that makes that chaos usable: stable virtual IPs, DNS names, ingress, and policy.

What you’ll understand after this level

• Why a Service exists and what problem it solves (stable virtual IP + load balancing across a dynamic set of pods)
• The four Service types: ClusterIP, NodePort, LoadBalancer, ExternalName
• How DNS in Kubernetes works (CoreDNS, search paths, the cluster domain)
• Ingress vs Service vs Gateway API — three layers, not the same thing
• NetworkPolicy — the k8s-native way to control pod-to-pod traffic
• CNI — how pods actually get IPs and L3 connectivity
• EndpointSlices — the scalable version of the Endpoints API

Notes in this level

Note	Status	What’s in it
Networking	🟡	Top-level mental model for k8s networking — the CNI model, namespaces, traffic flow
Services	✅	The four Service types (ClusterIP, NodePort, LoadBalancer, ExternalName), headless services, session affinity, externalTrafficPolicy
DNS	✅	CoreDNS, Service/Pod DNS names, ndots and the search path gotcha, headless DNS
Ingress	✅	The HTTP routing layer, ingressClassName, TLS, path rewrites, Ingress vs Gateway API
NetworkPolicy	✅	Pod-to-pod firewall rules, selectors, default-deny recipes, CNI-implementation differences
CNI	✅	How Pods actually get IPs, overlay vs underlay, plugin comparison (Flannel, Calico, Cilium)
Gateway API	✅	The role-aware successor to Ingress: GatewayClass, Gateway, HTTPRoute, ReferenceGrant, policy attachment, conformance, Ingress diff
EndpointSlices	🟡	Scalable endpoint tracking, topology hints, why it replaced Endpoints, the 100-endpoint limit
Networking Deep Dive	✅	Pod-to-pod, pod-to-service, service-to-external — packet-level walkthroughs, NAT, hairpin

Suggested reading order

1. Services — the foundational object after a Pod
2. DNS — how clients find Services (and the gotcha you’ll hit immediately)
3. EndpointSlices — what the Service is actually pointing at
4. Ingress — when you need HTTP routing from outside the cluster
5. NetworkPolicy — when you start designing multi-tenant or hardened clusters
6. CNI — understand the layer below all of this
7. Networking Deep Dive — when you need to debug, not before

Where to go next

→ L05 — Config & Storage: services are configured and persistent data lives somewhere.