What is Kubernetes operator pattern?

A Kubernetes Operator is a method of packaging, deploying, and managing a Kubernetes application — specifically stateful applications that require domain knowledge to manage correctly. Operators encode operational expertise into software that automates management of complex applications. Core concept: an Operator extends the Kubernetes API with custom resources (CRDs) and a controller that watches those resources and reconciles actual state to desired state. Example — Database Operator: define a PostgreSQLCluster CRD. Operator watches for PostgreSQLCluster objects → provisions primary + replicas, configures replication, handles failover, manages backups, handles scaling, performs rolling upgrades. The operator knows HOW to manage PostgreSQL; the user just declares WHAT they want: apiVersion: postgres.example.com/v1 kind: PostgreSQLCluster metadata: name: my-db spec: replicas: 3 version: "15" storage: 100Gi backupSchedule: "0 2 * * *". Building operators: Operator SDK: scaffold operator project, generate CRD manifests, Ansible/Helm/Go operators. Kubebuilder: framework for building operators in Go. KUDO: declarative operators with YAML. Level of operator maturity (Capability Model): Level 1: Basic Install; Level 2: Upgrades; Level 3: Full Lifecycle (backup/restore); Level 4: Deep Insights (metrics, alerts); Level 5: Auto Pilot (auto-scaling, self-healing, self-tuning). Production operators: Prometheus Operator (installs Prometheus, Alertmanager via CRDs), Cert-Manager (manages TLS certificates), External Secrets Operator, Argo CD, PostgreSQL operators (CloudNativePG, CrunchyData PGO), Kafka operators (Strimzi, Confluent).