function-resources-merger
An arbitrary resources merging function for Crossplane.

⚙️ Installing this function | 🔎 How-to-use | 🚀 Get started with an Example

This is a crossplane function that merges Kubernetes resources data and produces a single resulting resource containing the merged result. It supports any kind of resource.

Requirements

• crossplane ≥ v1.15 (recommended)

Installing this function

Important

It is recommended that this function is created with a custom DeploymentRuntimeConfig as to allow for the function to have the necessary permissions to get/update/create resources.

• Install using kubectl:

cat <<EOF | kubectl apply -f -
---
apiVersion: pkg.crossplane.io/v1beta1
kind: Function
metadata:
  name: function-xresources-merger
spec:
  package: ghcr.io/pcanilho/crossplane-function-resources-merger:v0.1.8
EOF

Tip

If different permissions are to be granted to the function, a (Cluster)Role and (Cluster)RoleBinding should be created and attached to the ServiceAccount managed by a DeploymentRuntimeConfig. Once you're ready, add the below block to the above document:

...
spec:
  ...
  runtimeConfigRef:
    apiVersion: pkg.crossplane.io/v1beta1
    kind: RuntimeConfig
    name: <your-DeploymentRuntimeConfig>

• Installing using helm:

# Chart.yaml
...
dependencies:
  - name: crossplane
    version: <your-crossplane-version>
    repository: https://charts.crossplane.io/master/
---
# values.yaml
crossplane:
  function:
    packages:
      - ghcr.io/pcanilho/crossplane-function-resources-merger:v0.1.8

The above Helm chart will install the pcanilho-crossplane-function-resources-merger function into the Crossplane runtime.

How-to-use

Function Input specification

debug [expand]

Optional

If set to true, the function will output debug information.

targetRef [expand]

Mandatory

Specifies the target resource that will be created/managed by this function.

Field	Description
namespace	The namespace where the target resource will be created/managed.
name	The name of the target composition resource name crossplane.io/composition-resource-name.
apiVersion	The API version of the target resource.
kind	The kind of the target resource.
key	The key to the root object field holding data. (defaults to data)

sourceRefs [expand]

Mandatory

A list of resources that will be used to merge into the target resource.

Field	Description
namespace	The namespace where the resource is located.
name	The name of the resource.
apiVersion	The API version of the resource.
kind	The kind of the resource.
key	The key to the root object field holding data. (defaults to data)
extractFromKey	(Optional) The key to extract the data from the resource.

Tip

Both targetRef and sourceRefs have full support for both standard kubernetes resources and custom-resources.

Specification

1. Select which is the target resource that will be created/managed by this function.
   • Examples: ConfigMap, EnvironmentConfig, etc.
   • Using a ConfigMap:

     targetRef:
       namespace: <target-namespace>
       name: <target-name>
       apiVersion: v1
       kind: ConfigMap

2. Identify which resources will be merged into the target resource.
   • Two ConfigMaps and a EnvironmentConfig:

     resources:
       - namespace: <resource-namespace>
         name: <resource-name>
         apiVersion: v1
         kind: ConfigMap
       - namespace: <resource-namespace>
         name: <resource-name>
         apiVersion: v1
         kind: ConfigMap
       - namespace: <resource-namespace>
         name: <resource-name>
         apiVersion: apiextensions.crossplane.io/v1alpha1
         kind: EnvironmentConfig

3. Define what merging options should be used through the XR resource.
   • Example:

     options:
       override: true
       appendSlice: true
       sliceDeepCopy: true
     transform:
       stringToMap: true

4. Observe the merged resource.
   • Example:

     apiVersion: v1
     kind: ConfigMap
     metadata:
       name: <target-name>
       namespace: <target-namespace>
     data:
       foo: bar

Note

ConfigMap and EnvironmentConfig resources are used as an example. This function can be used with any Kubernetes resource that contains a data field in its spec. Do note that the data-type compatibility of data spec field should to be taken into account when merging results.

Tip

The XR can be leveraged to define the merging boolean options.

➤ options (map)

Option	Type	Description
override	boolean	Merge override non-empty dst attributes with non-empty src attributes values.
typeCheck	boolean	Merge check types while overwriting it (must be used with override).
appendSlice	boolean	Merge append slices instead of overwriting it.
sliceDeepCopy	boolean	Merge slice element one by one with Overwrite flag.
overwriteEmptyValue	boolean	Merge override non-empty dst attributes with empty src attributes values.
overrideEmptySlice	boolean	Merge override empty dst slice with empty src slice.

➤ transform (map)

Option	Type	Description
stringToMap	boolean	String values will be transformed to maps when possible. Allowing for deep-merging.

➤ mode (string)

Option	Description
managed	The function will create a managed resource. (default)
unmanaged	The function will create an unmanaged resource. (deletion is not finalized by crossplane)

➤ debug (boolean)

Option	Description
true	The function will output debug information.
false	The function will not output debug information. (default)

Example (local)

Important

Goal: Merge 2xConfigMaps and 2xEnvironmentConfigs into a single resulting ConfigMap.

• ConfigMap (map-1):

  data:
    key1: a
    key2: b

• ConfigMap (map-2):

  data:
    key2: c
    key4: d

• EnvironmentConfig (envcfg-1):

  data:
    key1: e
    key6: f

• EnvironmentConfig (envcfg-2):

  data:
   key4: g
   key5: h

---

Composition ⚙️

---
apiVersion: apiextensions.crossplane.io/v1
kind: Composition
metadata:
  name: function-xresources-merger
spec:
  compositeTypeRef:
    apiVersion: resource-merger.canilho.net/v1alpha1
    kind: XR
  mode: Pipeline
  pipeline:
    - step: run
      functionRef:
        name: function-xresources-merger
      input:
        apiVersion: resources-merger.fn.canilho.net/v1alpha1
        kind: Input
        targetRef:
          namespace: ephemeral
          name: merged
          apiVersion: v1
          kind: ConfigMap
        sourceRefs:
          - namespace: ephemeral
            name: map-1
            apiVersion: v1
            kind: ConfigMap
          - namespace: ephemeral
            name: map-2
            apiVersion: v1
            kind: ConfigMap
          - namespace: ephemeral
            name: envcfg-1
            apiVersion: apiextensions.crossplane.io/v1alpha1
            kind: EnvironmentConfig
          - namespace: ephemeral
            name: envcfg-2
            apiVersion: apiextensions.crossplane.io/v1alpha1
            kind: EnvironmentConfig

XR ⚙️

---
apiVersion: resource-merger.fn.canilho.net/v1alpha1
kind: XR
metadata:
  name: merger-results-xr
spec:
  options:
    override: true
    appendSlice: true
    sliceDeepCopy: true
  transform:
    stringToMap: true

Function ⚙️

---
apiVersion: pkg.crossplane.io/v1beta1
kind: Function
metadata:
  name: function-xresources-merger
  annotations:
    # This tells crossplane beta render to connect to the function locally.
    render.crossplane.io/runtime: Development
spec:
  # This is ignored when using the Development runtime.
  package: function-xresources-merger

---

• The resulting ConfigMap (merged):

  ---
  apiVersion: v1
  kind: ConfigMap
  data:
    key1: e
    key2: c
    key4: g
    key5: h
    key6: f
  metadata:
    annotations:
      crossplane.io/composition-resource-name: merged
      generateName: merger-results-xr-
  ...

Test it out!

1. Launch the function locally in a separate shell:

     go run . --insecure --debug

2. Render the example:

   cd example && crossplane beta render xr.yaml composition.yaml functions.yaml -r

References

• functions: https://docs.crossplane.io/latest/concepts/composition-functions
• go: https://go.dev
• docker: https://www.docker.com
• cli: https://docs.crossplane.io/latest/cli