docs/content/v1.18/concepts/composite-resources.md

title	weight	description
Composite Resources	50	Composite resources, an XR or XRs, represent a collection of related cloud resources.

A composite resource represents a set of managed resources as a single Kubernetes object. Crossplane creates composite resources when users access a custom API, defined in the CompositeResourceDefinition.

{{<hint "tip" >}} Composite resources are a composite of managed resources.
A Composition defines how to compose the managed resources together. {{< /hint >}}

{{<expand "Confused about Compositions, XRDs, XRs and Claims?" >}} Crossplane has four core components that users commonly mix up:

• [Compositions]({{<ref "./compositions">}}) - A template to define how to create resources.
• [Composite Resource Definition]({{<ref "./composite-resource-definitions">}}) (XRD) - A custom API specification.
• Composite Resource (XR) - This page. Created by using the custom API defined in a Composite Resource Definition. XRs use the Composition template to create new managed resources.
• [Claims]({{<ref "./claims" >}}) (XRC) - Like a Composite Resource, but with namespace scoping. {{}}

Creating composite resources

Creating composite resources requires a [Composition]({{<ref "./compositions">}}) and a [CompositeResourceDefinition]({{<ref "./composite-resource-definitions">}}) (XRD).
The Composition defines the set of resources to create.
The XRD defines the custom API users call to request the set of resources.

XRDs define the API used to create a composite resource.
For example, this {{}}CompositeResourceDefinition{{}} creates a custom API endpoint {{}}xmydatabases.example.org{{}}.

apiVersion: apiextensions.crossplane.io/v1
kind: CompositeResourceDefinition
metadata: 
  name: xmydatabases.example.org
spec:
  group: example.org
  names:
    kind: xMyDatabase
    plural: xmydatabases
  # Removed for brevity

When a user calls the custom API, {{}}xmydatabases.example.org{{}}, Crossplane chooses the Composition to use based on the Composition's {{}}compositeTypeRef{{}}

apiVersion: apiextensions.crossplane.io/v1
kind: Composition
metadata:
  name: my-composition
spec:
  compositeTypeRef:
    apiVersion: example.org/v1alpha1
    kind: xMyDatabase
  # Removed for brevity

The Composition {{}}compositeTypeRef{{}} matches the XRD {{}}group{{}} and {{}}kind{{}}.

Crossplane creates the resources defined in the matching Composition and represents them as a single composite resource.

kubectl get composite
NAME                    SYNCED   READY   COMPOSITION         AGE
my-composite-resource   True     True    my-composition      4s

Naming external resources

By default, managed resources created by a composite resource have the name of the composite resource, followed by a random suffix.

For example, a composite resource named "my-composite-resource" creates external resources named "my-composite-resource-fqvkw."

Resource names can be deterministic by applying an {{}}annotation{{}} to the composite resource.

apiVersion: example.org/v1alpha1
kind: xMyDatabase
metadata:
  name: my-composite-resource
  annotations: 
    crossplane.io/external-name: my-custom-name
# Removed for brevity

Inside the Composition, use a {{}}patch{{}} to apply the external-name to the resources.

The {{}}fromFieldPath{{}} patch copies the {{}}metadata.annotations{{}} field from the composite resource to the {{}}metadata.annotations{{}} inside the managed resource.

{{<hint "note" >}} If a managed resource has the crossplane.io/external-name annotation Crossplane uses the annotation value to name the external resource. {{}}

apiVersion: apiextensions.crossplane.io/v1
kind: Composition
metadata:
  name: my-composition
spec:
  mode: Pipeline
  pipeline:
  - step: patch-and-transform
    functionRef:
      name: function-patch-and-transform
    input:
      apiVersion: pt.fn.crossplane.io/v1beta1
      kind: Resources
      resources:
      - name: database
        base:
          # Removed for brevity
        patches:
        - fromFieldPath: metadata.annotations
          toFieldPath: metadata.annotations

For more information on using function-patch-and-transform to patch resources refer to the [Function Patch and Transform]({{<ref "../guides/function-patch-and-transform">}}) documentation.

Composition selection

Select a specific Composition for a composite resource to use with {{}}compositionRef{{}}

{{<hint "important">}} The selected Composition must allow the composite resource to use it with a compositeTypeRef. Read more about the compositeTypeRef field in the [Enable Composite Resources]({{<ref "./compositions#enable-composite-resources">}}) section of the Composition documentation. {{< /hint >}}

apiVersion: example.org/v1alpha1
kind: xMyDatabase
metadata:
  name: my-composite-resource
spec:
  compositionRef:
    name: my-other-composition
  # Removed for brevity

A composite resource can also select a Composition based on labels instead of the exact name with a {{}}compositionSelector{{}}.

Inside the {{}}matchLabels{{}} section provide one or more Composition labels to match.

apiVersion: example.org/v1alpha1
kind: xMyDatabase
metadata:
  name: my-composite-resource
spec:
  compositionSelector:
    matchLabels:
      environment: production
  # Removed for brevity

Composition revision policy

Crossplane tracks changes to Compositions as [Composition revisions]({{<ref "composition-revisions">}}) .

A composite resource can use a {{}}compositionUpdatePolicy{{}} to manually or automatically reference newer Composition revisions.

The default {{}}compositionUpdatePolicy{{}} is "Automatic." Composite resources automatically use the latest Composition revision.

Change the policy to {{}}Manual{{}} to prevent composite resources from automatically upgrading.

apiVersion: example.org/v1alpha1
kind: xMyDatabase
metadata:
  name: my-composite-resource
spec:
  compositionUpdatePolicy: Manual
  # Removed for brevity

Composition revision selection

Crossplane records changes to Compositions as [Composition revisions]({{<ref "composition-revisions">}}).
A composite resource can select a specific Composition revision.

Use {{}}compositionRevisionRef{{}} to select a specific Composition revision by name.

For example, to select a specific Composition revision use the name of the desired Composition revision.

apiVersion: example.org/v1alpha1
kind: xMyDatabase
metadata:
  name: my-composite-resource
spec:
  compositionUpdatePolicy: Manual
  compositionRevisionRef:
    name: my-composition-b5aa1eb
  # Removed for brevity

{{<hint "note" >}} Find the Composition revision name from {{}}kubectl get compositionrevision{{}}

kubectl get compositionrevision
NAME                         REVISION   XR-KIND        XR-APIVERSION            AGE
my-composition-5c976ad       1          xmydatabases   example.org/v1alpha1     65m
my-composition-b5aa1eb       2          xmydatabases   example.org/v1alpha1     64m

{{< /hint >}}

A Composite resource can also select Composition revisions based on labels instead of the exact name with a {{}}compositionRevisionSelector{{}}.

Inside the {{}}matchLabels{{}} section provide one or more Composition revision labels to match.

apiVersion: example.org/v1alpha1
kind: xMyDatabase
metadata:
  name: my-composite-resource
spec:
  compositionRevisionSelector:
    matchLabels:
      channel: dev
  # Removed for brevity

Manage connection secrets

When a composite resource creates resources, Crossplane provides any [connection secrets]({{<ref "./managed-resources#writeconnectionsecrettoref">}}) to the composite resource.

{{<hint "important" >}}

A resource may only access connection secrets allowed by the XRD. By default XRDs provide access to all connection secrets generated by managed resources.
Read more about [managing connection secrets]({{<ref "./composite-resource-definitions#manage-connection-secrets">}}) in the XRD documentation. {{< /hint >}}

Use {{}}writeConnectionSecretToRef{{}} to specify where the composite resource writes their connection secrets to.

For example, this composite resource saves the connection secrets in a Kubernetes secret object named {{}}my-secret{{}} in the namespace {{}}crossplane-system{{}}.

apiVersion: example.org/v1alpha1
kind: xMyDatabase
metadata:
  name: my-composite-resource
spec:
  writeConnectionSecretToRef:
    name: my-secret
    namespace: crossplane-system
  # Removed for brevity

Composite resources can write connection secrets to an [external secret store]({{<ref "../guides/vault-as-secret-store">}}), like HashiCorp Vault.

{{<hint "important" >}} External secret stores are an alpha feature. Alpha features aren't enabled by default. {{< /hint >}}

Use the {{}}publishConnectionDetailsTo{{}} field to save connection secrets to an external secrets store.

apiVersion: example.org/v1alpha1
kind: xMyDatabase
metadata:
  name: my-composite-resource
spec:
  publishConnectionDetailsTo:
    name: my-external-secret-store
  # Removed for brevity

Read the [External Secrets Store]({{<ref "../guides/vault-as-secret-store">}}) documentation for more information on using external secret stores.

For more information on connection secrets read the [Connection Secrets knowledge base article]({{<ref "connection-details">}}).

Pausing composite resources

Crossplane supports pausing composite resources. A paused composite resource doesn't check or make changes on its external resources.

To pause a composite resource apply the {{}}crossplane.io/paused{{}} annotation.

apiVersion: example.org/v1alpha1
kind: xMyDatabase
metadata:
  name: my-composite-resource
  annotations:
    crossplane.io/paused: "true"
spec:
  # Removed for brevity

Verify composite resources

Use {{}}kubectl get composite{{}} to view all the composite resources Crossplane created.

kubectl get composite
NAME                    SYNCED   READY   COMPOSITION         AGE
my-composite-resource   True     True    my-composition      4s

Use kubectl get for the specific custom API endpoint to view only those resources.

kubectl get xMyDatabase.example.org
NAME                    SYNCED   READY   COMPOSITION        AGE
my-composite-resource   True     True    my-composition     12m

Use {{}}kubectl describe composite{{}} to view the linked {{}}Composition Ref{{}}, and unique managed resources created in the {{}}Resource Refs{{}}.

kubectl describe composite my-composite-resource
Name:         my-composite-resource
API Version:  example.org/v1alpha1
Kind:         xMyDatabase
Spec:
  Composition Ref:
    Name:  my-composition
  Composition Revision Ref:
    Name:                     my-composition-cf2d3a7
  Composition Update Policy:  Automatic
  Resource Refs:
    API Version:  s3.aws.upbound.io/v1beta1
    Kind:         Bucket
    Name:         my-composite-resource-fmrks
    API Version:  dynamodb.aws.upbound.io/v1beta1
    Kind:         Table
    Name:         my-composite-resource-wnr9t
# Removed for brevity

Composite resource conditions

The conditions of composite resources match the conditions of their managed resources.

Read the [conditions section]({{<ref "./managed-resources#conditions">}}) of the managed resources documentation for details.

Composite resource labels

Crossplane adds labels to composite resources to show their relationship to other Crossplane components.

Composite label

Crossplane adds the {{}} crossplane.io/composite{{}} label to all composite resources. The label matches the name of the composite. Crossplane applies the composite label to any managed resource created by a composite, creating a reference between the managed resource and owning composite resource.

kubectl describe xmydatabase.example.org/my-claimed-database-x9rx9
Name:         my-claimed-database2-x9rx9
Namespace:
Labels:       crossplane.io/composite=my-claimed-database-x9rx9

Claim name label

Crossplane adds the {{}}crossplane.io/claim-name{{}} label to composite resources created from a Claim. The label indicates the name of the Claim linked to this composite resource.

kubectl describe xmydatabase.example.org/my-claimed-database-x9rx9
Name:         my-claimed-database2-x9rx9
Namespace:
Labels:       crossplane.io/claim-name=my-claimed-database

Composite resources created directly, without using a Claim, don't have a {{}}crossplane.io/claim-name{{}} label.

Claim namespace label

Crossplane adds the {{}}crossplane.io/claim-namespace{{}} label to composite resources created from a Claim. The label indicates the namespace of the Claim linked to this composite resource.

kubectl describe xmydatabase.example.org/my-claimed-database-x9rx9
Name:         my-claimed-database2-x9rx9
Namespace:
Labels:       crossplane.io/claim-namespace=default

Composite resources created directly, without using a Claim, don't have a {{}}crossplane.io/claim-namespace{{}} label.