Image Configs

ImageConfig is an API for centralized control over the configuration of Crossplane package images. It allows you to configure package manager behavior for images globally, without needing to be referenced by other objects.

Configuring a pull secret

You can use ImageConfig to inject a pull secret into the Crossplane package manager registry client whenever it interacts with the registry, such as for dependency resolution or image pulls.

In the following example, the ImageConfig resource named acme-packages is configured to inject the pull secret named acme-registry-credentials whenever it needs to interact with the registry for images with the prefix registry1.com/acme-co/.

 1apiVersion: pkg.crossplane.io/v1beta1
 2kind: ImageConfig
 3metadata:
 4  name: acme-packages
 5spec:
 6  matchImages:
 7    - type: Prefix
 8      prefix: registry1.com/acme-co/
 9  registry:
10    authentication:
11      pullSecretRef:
12        name: acme-registry-credentials

spec.registry.authentication.pullSecretRef is a reference to the pull secret that should be injected into the registry client. The secret must be of type kubernetes.io/dockerconfigjson and must be in the Crossplane installation namespace, typically crossplane-system. One can create the secret using the following command:

1kubectl -n crossplane-system create secret docker-registry acme-registry-credentials --docker-server=registry1.com --docker-username=<user> --docker-password=<password>

Matching image references

spec.matchImages is a list of image references that the ImageConfig applies to. Each item in the list specifies the type and configuration of the image reference to match. The only supported type is Prefix, which matches the prefix of the image reference. No wildcards are supported. The type defaults to Prefix and can be omitted.

When there are multiple ImageConfigs matching an image reference, the one with the longest matching prefix is selected. If there are multiple ImageConfigs with the same longest matching prefix, one of them is selected arbitrarily. Please note that this situation occurs only if there are overlapping prefixes in the matchImages lists of different ImageConfig resources, which should be avoided.

Debugging

When the package manager selects an ImageConfig for a package, it throws an event with the reason ImageConfigSelection and the name of the selected ImageConfig and injected pull secret. You can find these events both on the package and package revision resources.

For example, the following event indicates that the ImageConfig named acme-packages was selected for the configuration named acme-configuration-foo:

1$ kubectl describe configuration acme-configuration-foo
2...
3Events:
4  Type     Reason                Age                From                                              Message
5  ----     ------                ----               ----                                              -------
6  Normal   ImageConfigSelection  45s                packages/configuration.pkg.crossplane.io          Selected pullSecret "acme-registry-credentials" from ImageConfig "acme-packages" for registry authentication

If you can’t find the expected event, ensure the prefix of the image reference matches the matchImages list of any ImageConfig resources in the cluster.

Configuring signature verification

You can use ImageConfig to configure signature verification for images. When signature verification is enabled, the package manager verifies the signature of each image before pulling it. If the signature isn’t valid, the package manager rejects the package deployment.

In the following example, the ImageConfig resource named verify-acme-packages is configured to verify the signature of images with the prefixes registry1.com/acme-co/configuration-foo and registry1.com/acme-co/configuration-bar.

In the example below, the ImageConfig resource named verify-acme-packages is set up to verify the signatures of images with the prefixes registry1.com/acme-co/configuration-foo and registry1.com/acme-co/configuration-bar.

 1apiVersion: pkg.crossplane.io/v1alpha1
 2kind: ImageConfig
 3metadata:
 4  name: verify-acme-packages
 5spec:
 6  matchImages:
 7    - type: Prefix
 8      prefix: registry1.com/acme-co/configuration-foo
 9    - type: Prefix
10      prefix: registry1.com/acme-co/configuration-bar
11  verification:
12    provider: Cosign
13    cosign:
14      authorities:
15        - name: verify acme packages
16          keyless:
17            url: https://fulcio.sigstore.dev
18            identities:
19              - issuer: https://token.actions.githubusercontent.com
20                subjectRegExp: https://github.com/acme-co/crossplane-packages/*
21          attestations:
22            - name: verify attestations
23              predicateType: spdxjson

spec.verification.provider specifies the signature verification provider. The only supported provider is Cosign. spec.verification.cosign contains the configuration for the Cosign provider. The authorities field contains the configuration for the authorities that sign the images. The attestations field contains the configuration for verifying the attestations of the images.

The ImageConfig API follows the same API shape as Policy Controller from Sigstore. Crossplane initially supports a subset of the Policy Controller configuration options which can be found in the API reference for the ImageConfig resource together with their descriptions.

When multiple authorities are provided, the package manager verifies the signature against each authority until it finds a valid one. If any of the authorities’ signatures are valid, the package manager accepts the image. Similarly, when multiple identities or attestations are provided, the package manager verifies until it finds a valid match and fails if none of them matches.

Matching the image reference to the ImageConfig works similarly to the pull secret configuration, as described in the previous section.

Checking the signature verification status

When signature verification is enabled, the respective controller reports the verification status as a condition of type Verified on the package revision resources. This condition indicates whether the signature verification was successful, failed, skipped, or incomplete due to an error.

Example conditions

Verification skipped: The package manager skipped signature verification for the package revision because there were no matching ImageConfig with signature verification configuration.

1  - lastTransitionTime: "2024-10-23T16:38:51Z"
2    reason: SignatureVerificationSkipped
3    status: "True"
4    type: Verified

Verification successful: The package manager successfully verified the signature of the image in the package revision.

1  - lastTransitionTime: "2024-10-23T16:43:05Z"
2    message: Signature verification succeeded with ImageConfig named "verify-acme-packages"
3    reason: VerificationSucceeded
4    status: "True"
5    type: Verified

Verification failed: The package manager failed to verify the signature of the image in the package revision.

1  - lastTransitionTime: "2024-10-23T16:42:44Z"
2    message: 'Signature verification failed with ImageConfig named "verify-acme-packages":
3      [signature keyless validation failed for authority verify acme packages
4      for registry1.com/acme-co/configuration-foo:v0.2.0: no signatures found: ]'
5    reason: SignatureVerificationFailed
6    status: "False"
7    type: Verified

Verification incomplete: The package manager encountered an error while verifying the signature of the image in the package revision.

1  - lastTransitionTime: "2024-10-23T16:44:22Z"
2    message: 'Error occurred during signature verification cannot get image verification
3      config: cannot get cosign verification config: no data found for key "cosign.pub"
4      in secret "cosign-public-key"'
5    reason: SignatureVerificationIncomplete
6    status: "False"
7    type: Verified

If you can’t see this condition on the package revision resource, namely ProviderRevision, ConfigurationRevision, or FunctionRevision, ensure that the feature is enabled.