What does an Ingress do and what does it require?

Ingress is an API object, not a proxy. You declare rules such as host api.example.com routing /v1 to one Service and /admin to another, plus TLS settings. An ingress controller such as NGINX, Traefik, Envoy or a cloud-native controller translates those rules into actual dataplane configuration.

• You must install and operate an ingress controller
• TLS certificates usually come from Secrets referenced by the Ingress
• Annotations are controller-specific and reduce portability
• Ingress is HTTP-focused; TCP and UDP need other mechanisms
• Gateway API is the newer, more expressive successor for many use cases

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: web
spec:
  ingressClassName: nginx
  tls:
    - hosts:
        - app.example.com
      secretName: app-tls
  rules:
    - host: app.example.com
      http:
        paths:
          - path: /
            pathType: Prefix
            backend:
              service:
                name: web
                port:
                  number: 80

Ingress controllers are shared infrastructure. A bad rule can affect every tenant behind the controller, and controller capacity, timeouts and body size limits become cluster-wide concerns. Treat the controller as a production service with its own monitoring, scaling and upgrade plan.