function-tag-manager

function-tag-manager is a Crossplane function that allows Platform Operators to manage Cloud tags on managed resources.

Currently only AWS resources that support tags are managed.

There several use cases for this Function:

• Allowing external systems to set tags on Crossplane Managed Resources without conflict.
• Adding Common Tags to Resources without having to update every resource in a Composition.
• Allowing users the ability to add their own tags when Requesting new resources.
• Removing tags that have been set earlier in the pipeline by other functions.

Installing the Function

The function is installed as a Crossplane Package. Apply the following YAML manifest to your Crossplane cluster.

apiVersion: pkg.crossplane.io/v1beta1
kind: Function
metadata:
  name: crossplane-contrib-function-tag-manager
spec:
  package: xpkg.upbound.io/crossplane-contrib/function-tag-manager:v0.4.0

Using this Function in a Composition

This function is designed to be a step in a Composition Pipeline after other functions have created Desired State. Below is an example pipeline step:

- step: manage-tags
  functionRef:
    name: crossplane-contrib-function-tag-manager
  input:
    apiVersion: tag-manger.fn.crossplane.io/v1beta1
    kind: ManagedTags
    addTags:
    - type: FromValue
      policy: Replace
      tags: 
        from: value
        add: tags
    - type: FromCompositeFieldPath
      fromFieldPath: spec.parameters.additionalTags
      policy: Replace
    - type: FromCompositeFieldPath
      fromFieldPath: spec.parameters.optionalTags
      policy: Retain
    ignoreTags:
    - type: FromValue
      policy: Replace
      keys:
      - external-tag-1
      - external-tag-2
    - type: FromCompositeFieldPath
      fromFieldPath: spec.parameters.ignoreTagKeysReplace
      policy: Replace
    - type: FromCompositeFieldPath
      fromFieldPath: spec.parameters.ignoreTagKeyRetain
      policy: Retain

Function Inputs

AddTags

The addTags field configures tags that will be added to every resource.

The FromValue type indicates that tags will be defined in the function input.

The FromCompositeField type indicates that the tags will be imported from the Composite Resource manifest.

   addTags:
    - type: FromValue
      policy: Replace
      tags: 
        from: value
        add: tags
    - type: FromCompositeFieldPath
      fromFieldPath: spec.parameters.additionalTags
      policy: Replace
    - type: FromCompositeFieldPath
      fromFieldPath: spec.parameters.optionalTags
      policy: Retain

IgnoreTags

The ignoreTags configures Observed tags in the Cloud that Crossplane will "ignore". In most cases, Crossplane will attempt to manage every field of a resource, and if a difference is calculated Crossplane will update the resource and remove fields that are not in the Desired state.

There are many Cloud management systems that set tags on Resources. By adding the keys to those tags in the ignoreTags section, the function will populate the Desired state with the values of the Observed tags for each key defined.

Tag keys to ignore can be defined in FromValue or set in the Composite/Claim using FromCompositeFieldPath.

ignoreTags:
- type: FromValue
  policy: Replace
  keys:
  - external-tag-1
  - external-tag-2
- type: FromCompositeFieldPath
  fromFieldPath: spec.parameters.ignoreTagKeysReplace
  policy: Replace
- type: FromCompositeFieldPath
  fromFieldPath: spec.parameters.ignoreTagKeysRetain
  policy: Retain

Another option for allowing external systems to manage tags is to use the initProvider field of a Managed Resource.

RemoveTags

The function can remove tags defined in the desired state by specifying removeTags and providing an array of keys to delete.

  removeTags:
  - type: FromValue
    keys: 
    - fromValue2
  - type: FromCompositeFieldPath
    fromFieldPath: spec.parameters.removeTags

Tag Policies

When Merging tags, a Policy can be set:

• Replace (default) in the case the desired and observed tags don't match, the observed value will replace desired.
• Retain in the case the desired and observed tags don't match, the desired value will remain.

Skipping Resources Manually

This function will skip any resource with the tag-manager.fn.crossplane.io/ignore-resource Kubernetes label set to True or true:

apiVersion: ec2.aws.upbound.io/v1beta1
kind: InternetGateway
metadata:
  labels:
    tag-manager.fn.crossplane.io/ignore-resource: "True"
  name: my-igw

Filtering Resources

This function currently supports a subset of AWS that allow setting of tags.

A scan of the 1.14 AWS provider shows that 475 resources support tags and 482 do not. The Provider CRDs were scanned to generate the list in filter.go.

Developing this Function

# Run code generation - see input/generate.go
$ go generate ./...

# Run tests
$ go test -cover ./...
ok      github.com/stevendborrelli/function-tag-manager 0.398s  coverage: 67.9% of statements
        github.com/stevendborrelli/function-tag-manager/input/v1beta1           coverage: 0.0% of statements

# Lint the code
$ docker run --rm -v $(pwd):/app -v ~/.cache/golangci-lint/v1.61.0:/root/.cache -w /app golangci/golangci-lint:v1.61.0 golangci-lint run

# Build a Docker image - see Dockerfile
$ docker build .

Testing this Function

To test this function, it can be run locally in debug mode:

# Run your Function in insecure mode
go run . --insecure --debug

Once your Function is running, in another window you can use the render command.

# Install Crossplane CLI
$ curl -sL https://raw.githubusercontent.com/crossplane/crossplane/master/install.sh | XP_CHANNEL=stable sh

To build the function, run:

docker build . --tag=function-tag-manager

Please note that this command builds an image for your local computer architecture. In general, Crossplane projects build images for linux/amd64 and linux/arm64. See the Github ci.yaml workflow for an example.

Next create the Crossplane Package, embedding the function we just built:

crossplane xpkg build -f package --embed-runtime-image=function-tag-manager -o function-tag-manager.xpkg

I use the up binary to push to the Upbound Marketplace

up xpkg push xpkg.upbound.io/crossplane-contrib/function-tag-manager:v0.4.0 -f function-tag-manager.xpkg