Mutating Registry Webhook
A Kubernetes mutating admission webhook that automatically rewrites container image references to use pull-through cache registries (like AWS ECR Pull Through Cache).
Description
This webhook intercepts Pod creation and update requests in your Kubernetes cluster and automatically rewrites container image references based on configurable rules. This is particularly useful when you want to:
Use AWS ECR Pull Through Cache to reduce external registry dependencies
Implement a corporate image proxy/cache
Redirect images from Docker Hub, GCR, Quay.io, or other registries to your internal registry
Apply different rules based on namespaces or pod labels
Features
π Automatic image URL rewriting based on regex patterns
π― Namespace and label-based targeting
β‘ High-performance with in-memory rule caching
π Secure by default with cert-manager integration
π Prometheus metrics support
ποΈ Helm chart for easy deployment
π§ͺ Comprehensive test coverage
Getting Started
Prerequisites
go version v1.24.0+
docker version 17.03+
kubectl version v1.11.3+
Access to a Kubernetes v1.11.3+ cluster
cert-manager v1.0+ installed in your cluster
Quick Start
Install cert-manager (if not already installed):
kubectl apply -f https://github.com/cert-manager/cert-manager/releases/download/v1.13.0/cert-manager.yaml
Install the webhook:
kubectl apply -f https://github.com/flemzord/mutating-registry-webhook/releases/download/v0.2.0/install.yaml
Create a RegistryRewriteRule:
apiVersion : dev.flemzord.fr/v1alpha1 kind : RegistryRewriteRule metadata : name : docker-hub-to-ecr spec : rules : # Redirect Docker Hub images to ECR pull-through cache - match : ' ^docker\.io/(.*) ' replace : ' 123456789012.dkr.ecr.us-east-1.amazonaws.com/dockerhub/$1 ' # Handle images without explicit registry (defaults to docker.io) - match : ' ^([^/]+/[^/]+)$ ' replace : ' 123456789012.dkr.ecr.us-east-1.amazonaws.com/dockerhub/$1 '
To Deploy on the cluster
Build and push your image to the location specified by IMG :
make docker-build docker-push IMG= < some-registry > /mutating-registry-webhook:tag
NOTE: This image ought to be published in the personal registry you specified. And it is required to have access to pull the image from the working environment. Make sure you have the proper permission to the registry if the above commands donβt work.
Install the CRDs into the cluster:
make install
Deploy the Manager to the cluster with the image specified by IMG :
make deploy IMG= < some-registry > /mutating-registry-webhook:tag
NOTE: If you encounter RBAC errors, you may need to grant yourself cluster-admin privileges or be logged in as admin.
Create instances of your solution You can apply the samples (examples) from the config/sample:
kubectl apply -k config/samples/
NOTE: Ensure that the samples has default values to test it out.
To Uninstall
Delete the instances (CRs) from the cluster:
kubectl delete -k config/samples/
Delete the APIs(CRDs) from the cluster:
make uninstall
UnDeploy the controller from the cluster:
make undeploy
Project Distribution
Following the options to release and provide this solution to the users.
By providing a bundle with all YAML files
Build the installer for the image built and published in the registry:
make build-installer IMG= < some-registry > /mutating-registry-webhook:tag
NOTE: The makefile target mentioned above generates an 'install.yaml' file in the dist directory. This file contains all the resources built with Kustomize, which are necessary to install this project without its dependencies.
Using the installer
Users can just run 'kubectl apply -f ' to install the project, i.e.:
kubectl apply -f https://raw.githubusercontent.com/ < org > /mutating-registry-webhook/ < tag or branch > /dist/install.yaml
By providing a Helm Chart
Build the chart using the optional helm plugin
kubebuilder edit --plugins=helm/v1-alpha
See that a chart was generated under 'dist/chart', and users can obtain this solution from there.
NOTE: If you change the project, you need to update the Helm Chart using the same command above to sync the latest changes. Furthermore, if you create webhooks, you need to use the above command with the '--force' flag and manually ensure that any custom configuration previously added to 'dist/chart/values.yaml' or 'dist/chart/manager/manager.yaml' is manually re-applied afterwards.
Examples
Basic Docker Hub to ECR
apiVersion : dev.flemzord.fr/v1alpha1 kind : RegistryRewriteRule metadata : name : dockerhub-cache spec : rules : - match : ' ^docker\.io/(.*) ' replace : ' ${ECR_REGISTRY}/dockerhub/$1 ' - match : ' ^([^/]+/[^/]+)$ ' # nginx:latest becomes docker.io/nginx:latest replace : ' ${ECR_REGISTRY}/dockerhub/$1 '
Multiple Registries
apiVersion : dev.flemzord.fr/v1alpha1 kind : RegistryRewriteRule metadata : name : multi-registry-cache spec : rules : # Docker Hub - match : ' ^docker\.io/(.*) ' replace : ' ${ECR_REGISTRY}/dockerhub/$1 ' # Google Container Registry - match : ' ^gcr\.io/([^/]+)/(.+) ' replace : ' ${ECR_REGISTRY}/gcr/$1/$2 ' # Quay.io - match : ' ^quay\.io/(.*) ' replace : ' ${ECR_REGISTRY}/quay/$1 ' # GitHub Container Registry - match : ' ^ghcr\.io/(.*) ' replace : ' ${ECR_REGISTRY}/ghcr/$1 '
Namespace-Specific Rules
apiVersion : dev.flemzord.fr/v1alpha1 kind : RegistryRewriteRule metadata : name : production-only spec : rules : - match : ' ^docker\.io/(.*) ' replace : ' ${PROD_REGISTRY}/$1 ' conditions : namespaces : ["production", "staging"]
Label-Based Rules
apiVersion : dev.flemzord.fr/v1alpha1 kind : RegistryRewriteRule metadata : name : team-specific spec : rules : - match : ' ^docker\.io/(.*) ' replace : ' ${TEAM_REGISTRY}/$1 ' conditions : labels : team : " platform " cache : " enabled "
Architecture
The webhook consists of:
CRD (RegistryRewriteRule): Defines rewrite rules with regex patterns Mutating Webhook: Intercepts Pod creation/update and applies rules Rules Controller: Watches for rule changes and updates the cache In-Memory Cache: Provides O(1) rule lookup performance
Troubleshooting
Check if the webhook is running:
kubectl get pods -n mutating-registry-webhook-system
View webhook logs:
kubectl logs -n mutating-registry-webhook-system deployment/mutating-registry-webhook-controller-manager
Test with a sample pod:
kubectl run test --image=nginx:latest --dry-run=server -o yaml
Disable mutation for specific pods:
Add the annotation rewrite-disabled: "true" to your pod:
metadata : annotations : rewrite-disabled : " true "
Performance
Rule compilation: O(n) on startup/rule change
Image mutation: O(1) with cached rules
Benchmarks: ~0.7ΞΌs per image mutation
Memory usage: ~50MB base + rules
Contributing
We welcome contributions! Please see our Contributing Guide for details.
NOTE: Run make help for more information on all potential make targets
More information can be found via the Kubebuilder Documentation
License
Copyright 2025 flemzord.
Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.