Helm, Kustomize and Plain Manifests

Templates versus overlays

Plain manifests with kubectl apply are fine for one small app in one environment. Kustomize, built into kubectl apply -k, takes plain YAML bases and applies overlays and patches per environment, with no templating language; it is simple and transparent, but has no packaging, versioning, dependency management or release history. Helm adds parameterised templates, packaging and distribution, dependencies, lifecycle hooks and release history with rollback; the cost is Go templating, which can become hard to read. The tools combine well: Helm's --post-renderer option passes rendered output through a program such as Kustomize to patch third-party charts without forking them, and Argo CD and Flux can both use Kustomize on top of Helm output. A sensible default: install third-party software with its Helm chart, and choose either Helm or Kustomize for your own apps based on whether you need distribution and parameters or just per-environment patches.

Comparing the approaches

A quick decision aid.

need                                          tool
--------------------------------------------  ----------------------------
install third-party software with options     Helm chart from the vendor
small in-house app, per-env patches only      Kustomize overlays
share an app across many teams / customers    Helm chart in an OCI registry
patch a vendor chart without forking it       Helm --post-renderer + Kustomize
releases with history and one-step rollback   Helm (or a GitOps controller on top)

A form letter versus sticky notes

Helm is a form letter with blanks to fill in for each recipient. Kustomize is a finished letter with sticky notes saying "for Mumbai office, change line 3". Both work; choose by how many variations you send out.

Quick check: Which feature does Kustomize lack compared with Helm?

• Per-environment patches
• Release history with rollback and chart packaging
• Plain YAML bases
• Integration with kubectl