Ever found yourself thinking, “Kubernetes is awesome, but I wish it could do this specific thing just for my setup”? Well, guess what? It probably can. Kubernetes isn’t just about managing those swanky Pods and Services; it’s like a LEGO set, and with the right pieces, you can build pretty much anything.<\/p>\r\n\r\n\r\n\r\n
Enter the world of Custom Resource Definitions, or CRDs for the cool kids. Imagine being able to teach your Kubernetes new tricks without waiting for the next big release. That’s exactly what CRDs let you do!<\/p>\r\n\r\n\r\n\r\n
In this blog post, we will explore how to extend the Kubernetes API with Custom Resource Definitions (CRDs).<\/p>\r\n
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Topics To be covered :<\/p>\r\n\r\n\r\n\r\n
1. The Basics: API Groups and Versions<\/strong><\/p>\r\n\r\n\r\n\r\n 2. Resources and Kinds<\/strong><\/p>\r\n\r\n\r\n\r\n 3. Object Metadata<\/strong> Every Kubernetes resource comes with metadata. This section usually includes details like:<\/p>\r\n\r\n\r\n\r\n 4. Spec and Status<\/strong> Almost every Kubernetes resource has these two main fields:<\/p>\r\n\r\n\r\n\r\n 5. API Endpoints<\/strong> For every resource, there are specific API endpoints. These are the URLs you’d hit if you were to interact directly with the Kubernetes API server. For instance, Before you can use a custom resource in Kubernetes, you need to define it, usually in Golang. Here is how you can do it.<\/p>\r\n\r\n\r\n\r\n To generate a deepcopy we would use controller-gen<\/a> run the below command to install at Since now we have created a Go scheme for our custom resource we need to register this resource in the k8s. We have to create a definition for that i.e. custom resource definition<\/p>\r\n\r\n\r\n\r\n We would use controller-gen to create a CRD manifest. Go to the root of the repo and run : This command will:<\/p>\r\n\r\n\r\n\r\n If you have a Kubernetes cluster ready and you want to apply the CRDs, you can use kubectl: Blog Pundits: Sandeep Rawat<\/a><\/strong><\/p>\r\n \r\n\r\n<\/p>\r\n OpsTree<\/a><\/strong> is an End-to-End DevOps Solution Provider.<\/p>\r\n \r\n\r\n<\/p>\r\n\r\n
core<\/code>, apps<\/code>, batch<\/code>, extensions<\/code>, and more. These groups represent various functionalities and components.<\/li>\r\n\r\n\r\n\r\nv1<\/code>, v1beta1<\/code>, etc. This is because the Kubernetes API evolves over time, and different versions can coexist.<\/li>\r\n<\/ul>\r\n\r\n\r\n\r\n\r\n
Pods<\/code>, Services<\/code>, and Nodes<\/code> are all examples of resources.<\/li>\r\n\r\n\r\n\r\nkind<\/code>. For instance, the kind for a Pod is Pod<\/code>, and for a Service, it’s Service<\/code>.<\/li>\r\n<\/ul>\r\n\r\n\r\n\r\n\r\n
name<\/code>: Unique within a namespace, used to identify the resource.<\/li>\r\n\r\n\r\n\r\nnamespace<\/code>: Helps with the resource’s scope. Some resources are cluster-scoped (like Node<\/code>), while others are namespace-scoped (like Pod<\/code>).<\/li>\r\n\r\n\r\n\r\nlabels<\/code> and annotations<\/code>: Key-value pairs that you can attach to resources for various purposes, from organizational patterns to notes.<\/li>\r\n<\/ul>\r\n\r\n\r\n\r\n\r\n
\/api\/v1\/namespaces\/{namespace}\/pods\/{pod}<\/code> would be an endpoint for a specific pod.<\/p>\r\n\r\n\r\n
\r\n\r\n\r\nRegistering a Custom API in Golang<\/h2>\r\n\r\n\r\n\r\n
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package v1\r\n\r\ntype MyCustomResourceSpec struct {\r\n Field1 string `json:\"field1,omitempty\"`\r\n Field2 int `json:\"field2,omitempty\"`\r\n}\r\n\r\ntype MyCustomResource struct {\r\n metav1.TypeMeta `json:\",inline\"`\r\n metav1.ObjectMeta `json:\"metadata,omitempty\"`\r\n\r\n Spec MyCustomResourceSpec `json:\"spec,omitempty\"`\r\n Status MyCustomResourceStatus `json:\"status,omitempty\"`\r\n}\r\n\r\ntype MyCustomResourceList struct {\r\n metav1.TypeMeta `json:\",inline\"`\r\n metav1.ListMeta `json:\"metadata,omitempty\"`\r\n Items []MyCustomResource `json:\"items\"`\r\n}<\/pre>\r\n\r\n\r\n\r\n\r\n
type Object interface {\r\n GetObjectKind() schema.ObjectKind\r\n DeepCopyObject() Object\r\n}<\/pre>\r\n\r\n\r\n\r\n$GOPATH\/bin\/<\/code><\/p>\r\n\r\n\r\n\r\ngo install sigs.k8s.io\/controller-tools\/cmd\/controller-gen@latest<\/pre>\r\n\r\n\r\n\r\n
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\/\/ +kubebuilder:object:root=true<\/code> as suggested here<\/a>. We need to put this tag on MyCustomResource<\/code> and MyCustomResourceList<\/code> to generate deepcopy for that as given below. This would generate a file zz_deepcopy.go in the same directory.<\/li>\r\n<\/ol>\r\n\r\n\r\n\r\n\/\/ +kubebuilder:object:root=true\r\ntype MyCustomResource struct {\r\n metav1.TypeMeta `json:\",inline\"`\r\n metav1.ObjectMeta `json:\"metadata,omitempty\"`\r\n\r\n Spec MyCustomResourceSpec `json:\"spec,omitempty\"`\r\n Status MyCustomResourceStatus `json:\"status,omitempty\"`\r\n}\r\n\r\n\/\/ +kubebuilder:object:root=true\r\ntype MyCustomResourceList struct {\r\n metav1.TypeMeta `json:\",inline\"`\r\n metav1.ListMeta `json:\"metadata,omitempty\"`\r\n Items []MyCustomResource `json:\"items\"`\r\n}<\/pre>\r\n\r\n\r\n\r\nCreating a Custom Resource definition (CRD) to Register the Custom Resource<\/h2>\r\n\r\n\r\n\r\n
controller-gen crd:crdVersions=v1 paths=\".\/...\" output:dir=\".\/crd\"<\/code><\/p>\r\n\r\n\r\n\r\n\r\n
kubectl apply -f .\/crd<\/code><\/p>\r\n