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Merge Generator

The Merge generator combines parameters produced by the base (first) generator with matching parameter sets produced by subsequent generators. A matching parameter set has the same values for the configured merge keys. Non-matching parameter sets are discarded. Override precedence is bottom-to-top: the values from a matching parameter set produced by generator 3 will take precedence over the values from the corresponding parameter set produced by generator 2.

Using a Merge generator is appropriate when a subset of parameter sets require overriding.

Example: Base Cluster generator + override Cluster generator + List generator

As an example, imagine that we have two clusters:

  • A staging cluster (at https://1.2.3.4)
  • A production cluster (at https://2.4.6.8)

yaml apiVersion: argoproj.io/v1alpha1 kind: ApplicationSet metadata: name: cluster-git spec: generators: # merge 'parent' generator - merge: mergeKeys: - server generators: - clusters: values: kafka: 'true' redis: 'false' # For clusters with a specific label, enable Kafka. - clusters: selector: matchLabels: use-kafka: 'false' values: kafka: 'false' # For a specific cluster, enable Redis. - list: elements: - server: https://2.4.6.8 values.redis: 'true' template: metadata: name: '{{name}}' spec: project: '{{metadata.labels.environment}}' source: repoURL: https://github.com/argoproj/applicationset.git targetRevision: HEAD path: app helm: parameters: - name: kafka value: '{{values.kafka}}' - name: redis value: '{{values.redis}}' destination: server: '{{server}}' namespace: default

The base Cluster generator scans the set of clusters defined in Argo CD, finds the staging and production cluster secrets, and produces two corresponding sets of parameters: ```yaml - name: staging server: https://1.2.3.4 values.kafka: 'true' values.redis: 'false'

  • name: production server: https://2.4.6.8 values.kafka: 'true' values.redis: 'false' ```

The override Cluster generator scans the set of clusters defined in Argo CD, finds the staging cluster secret (which has the required label), and produces the following parameters: yaml - name: staging server: https://1.2.3.4 values.kafka: 'false'

When merged with the base generator's parameters, the values.kafka value for the staging cluster is set to 'false'. ```yaml - name: staging server: https://1.2.3.4 values.kafka: 'false' values.redis: 'false'

  • name: production server: https://2.4.6.8 values.kafka: 'true' values.redis: 'false' ```

Finally, the List cluster generates a single set of parameters: yaml - server: https://2.4.6.8 values.redis: 'true'

When merged with the updated base parameters, the values.redis value for the production cluster is set to 'true'. This is the merge generator's final output: ```yaml - name: staging server: https://1.2.3.4 values.kafka: 'false' values.redis: 'false'

  • name: production server: https://2.4.6.8 values.kafka: 'true' values.redis: 'true' ```

Restrictions

  1. You should specify only a single generator per array entry. This is not valid: ```yaml
  2. merge: generators:
    • list: # (...) git: # (...) ```
    • While this will be accepted by Kubernetes API validation, the controller will report an error on generation. Each generator should be specified in a separate array element, as in the examples above.
  3. The Merge generator does not support template overrides specified on child generators. This template will not be processed: ```yaml
  4. merge: generators:
    • list: elements: - # (...) template: { } # Not processed ```
  5. Combination-type generators (Matrix or Merge) can only be nested once. For example, this will not work: ```yaml
  6. merge: generators:
    • merge: generators: - merge: # This third level is invalid. generators: - list: elements: - # (...) ```