Using Metadata Labels and CEL Expressions

Use cluster metadata labels and CEL expressions to create dynamic Plugin configurations.

Overview

Greenhouse allows you to define metadata labels on Clusters and use them in PluginPreset configurations through CEL (Common Expression Language) expressions. This enables dynamic configuration of Plugins based on cluster-specific attributes like region, environment, or any custom metadata.

For information on setting metadata labels on Clusters, see Setting Metadata Labels.

Using Expressions with PluginPresets

Expressions are particularly powerful with PluginPresets, allowing you to deploy Plugins to multiple clusters with cluster-specific configurations:

apiVersion: greenhouse.sap/v1alpha1
kind: PluginPreset
metadata:
  name: monitoring-preset
  namespace: example-organization
spec:
  clusterSelector:
    matchLabels:
      metadata.greenhouse.sap/tier: premium
  plugin:
    pluginDefinitionRef:
      kind: PluginDefinition
      name: kube-monitoring
    releaseNamespace: monitoring
    optionValues:
      - name: prometheus.remoteWrite.url
        expression: "https://thanos.${global.greenhouse.metadata.region}.example.com/api/v1/receive"
      - name: grafana.dashboards.annotations
        expression: |
          cluster: ${global.greenhouse.clusterName}
          region: ${global.greenhouse.metadata.region}
          environment: ${global.greenhouse.metadata.environment}

This PluginPreset will:

  1. Select all clusters with the metadata.greenhouse.sap/tier: premium label
  2. Create a Plugin for each matching cluster
  3. Resolve expressions using each cluster’s specific metadata

Available Variables

The following global.greenhouse.* variables are available in expressions:

VariableDescription
global.greenhouse.clusterNameThe name of the target cluster
global.greenhouse.organizationNameThe name of the organization
global.greenhouse.baseDomainDNS base domain for Greenhouse
global.greenhouse.ownedByThe owning team of the Plugin
global.greenhouse.metadata.*Cluster metadata labels

⚠️ global.greenhouse.clusterNames and global.greenhouse.teamNames were removed. An expression still referencing either of them fails to evaluate and blocks the PluginPreset from rolling out its Plugins. See Injected Greenhouse Values.

Using CEL Functions

CEL string functions can transform values:

optionValues:
  # Convert to uppercase
  - name: clusterLabel
    expression: ${global.greenhouse.clusterName.upperAscii()}

  # Split and rejoin with different delimiter
  - name: normalizedName
    expression: ${global.greenhouse.clusterName.split('-').join('_')}

  # Check if environment contains a substring
  - name: isProduction
    expression: ${global.greenhouse.metadata.environment.contains('prod')}

For a complete list of available CEL string functions, see the CEL string extension documentation.

Next Steps