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Hydra User Manual

Value Layering Overview

hydra-gitops/hydra

Value Layering Overview¶

How values are merged from multiple sources into the final rendered output.

Merge Order¶

Values merge bottom-up. Later sources override earlier ones:

1. charts-repository/apps/<group>/<app>/values.yaml         (base defaults)
        ↓ deep merge
2. gitops-repository/clusters/<cluster>/<group>/values.yaml (group-level override)
        ↓ deep merge
3. gitops-repository/clusters/<cluster>/<group>/in-cluster/<app>/values.yaml (app-level override)
        ↓ deep merge
4. Hydra ConfigMaps on cluster                              (runtime injection)

Merge Semantics¶

Maps — Deep merged. Nested keys are merged individually. A key in a later layer overrides the same key from an earlier layer.
Lists — Replaced entirely. A list in a later layer replaces (not appends to) the same list from an earlier layer.
Scalars — Replaced. A scalar in a later layer overrides the earlier value.

Example: Value Flow¶

Given a chart with refs.events defined in the charts-repo:

# charts-repository/apps/cluster-infra/cert-manager/values.yaml
global:
  hydra:
    refs:
      events:
        tag: [uninstall]
        predicate: 'gvk == "events.k8s.io/v1/Event" && ns == "cert-manager"'

And a cluster override adding an additional ref group:

# gitops-repository/clusters/prod/cluster-infra/in-cluster/cert-manager/values.yaml
global:
  hydra:
    refs:
      custom-secret:
        tag: [backup]
        predicate: 'kind == "Secret" && ns == "cert-manager" && name == "ca-key"'

The effective result has both ref groups (deep merge of the refs map).

Where to Define What¶

Value type	Where	Why
Ref definitions	Charts repo	Part of the app's dependency model
Preset overrides	Charts repo or GitOps repo	Depends on whether it's app-global or cluster-specific
`kubectl.allowedContexts`	GitOps repo	Cluster-specific
`path`, `revision`, `repository`	GitOps repo	Cluster/environment metadata
`kubernetesVersion`	GitOps repo	Cluster-specific

Inspecting Effective Values¶

# Without cluster ConfigMaps
hydra local values prod.cluster-infra.cert-manager

# With cluster ConfigMaps merged
hydra gitops values prod.cluster-infra.cert-manager

See Also¶