76 lines
2.9 KiB
Markdown
76 lines
2.9 KiB
Markdown
# Replacement Transformer
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This plugin is written in `go` and uses the `kyaml` and `airshipctl` libraries
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for parsing the input and writing the output.
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## Function implementation
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The function is implemented as an [image](image), and built using `make image`.
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Function reads configuration, a collection of input resources, and performs values
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replacement based on configuration.
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## Function invocation
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The function is invoked by authoring a [local Resource](local-resource)
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with `metadata.annotations.[config.kubernetes.io/function]` and running:
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kustomize config run local-resource/
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This exits non-zero if there is an error.
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## Running the Example
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Run `Replacement Transformer` with:
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kustomize fn run local-resource --dry-run
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Value of `spec.version` in resource `KubeadmControlPlane` (`v1.18.6`) will be replaced
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with value of `kubernetes` field defined in `VariableCatalogue` resource
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## Configuration file format
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`Replacement Transformer` configuration resource is represented as a standard
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k8s resource with Group, Version, Kind and Metadata header. Replacement
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configuration is defined under `replacements` field which contains a list of
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object with following structure.
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source:
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objref:
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group: airshipit.org
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version: v1alpha1
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kind: Clusterctl
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name: resource-name
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namespace: capm3
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value: "string value"
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fieldref: {.data.host}
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target:
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objref:
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group: airshipit.org
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version: v1alpha1
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kind: KubeConfig
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name: resource-name
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namespace: capi-system
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fieldrefs:
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- {.config.kind}
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* `source` defines where a substitution is from. It can from two different
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kinds of sources from a field of one resource or from a string.
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* `objref` refers to a kubernetes object by Group, Version, Kind, Name and
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Namespace. Each field can be omitted or be an empty string.
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* `value` static string value to substitute into `target`.
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* `fieldref` JSON path to particular object field. This field essentially
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represents JSON query with syntax used in `kubectl` executed with
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flag `--jsonpath`. JSON path syntax end elements is defined by
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https://goessner.net/articles/JsonPath/
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* `target` defines a substitution target.
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* `objref` specifies a set of resources. Any resource that matches
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intersection of all conditions (Group, Version, Kind, Name and Namespace) is
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included in this set.
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* `fieldrefs` list of JSON path strings which identify target field to
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substitute into. Field reference may have include pattern which is used as a
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replacement variable. For example in following query `{.metadata.name}%NAME%`
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string surrounded by `%` symbols (i.e. `NAME`) is considered as a pattern
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inside a field value identified by JSON path `metadata.name`. Therefore if
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value of `metadata.name` is `some-NAME-of-the-pod` only `NAME` substring is
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replaced with the string defined by substitution source.
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