ArgoCD ApplicationSets: Multi-Cluster GitOps at Scale

If you run more than three Kubernetes clusters or more than ten ArgoCD Applications, you have already felt the pain. Every new tenant, region, or feature flag means another Application YAML, another pull request, another copy-paste mistake waiting to happen. ArgoCD ApplicationSets are the controller-driven answer: one CRD describes a template and a set of generators, and the controller materializes the cartesian product as real ArgoCD Applications — reconciled, drift-corrected, and torn down when the inputs go away.

This deep dive walks through the generators that matter in production (List, Cluster, Git, Matrix, Pull Request), shows three real patterns we lean on at scale, and ends with the gotchas that bite teams adopting ApplicationSets in 2026 with ArgoCD 3.3.