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Admission_Webhooks.md

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graph LR
    Webhook_Server_Manager["Webhook Server/Manager"]
    Cluster_Webhook_Handler["Cluster Webhook Handler"]
    Machine_Webhook_Handler["Machine Webhook Handler"]
    Kubernetes_API_Server["Kubernetes API Server"]
    Cluster_CRD["Cluster CRD"]
    Machine_CRD["Machine CRD"]
    Core_Cluster_API_Controllers["Core Cluster API Controllers"]
    Webhook_Server_Manager -- "registers with" --> Kubernetes_API_Server
    Kubernetes_API_Server -- "sends requests to" --> Webhook_Server_Manager
    Webhook_Server_Manager -- "dispatches requests to" --> Cluster_Webhook_Handler
    Webhook_Server_Manager -- "dispatches requests to" --> Machine_Webhook_Handler
    Cluster_Webhook_Handler -- "operates on" --> Cluster_CRD
    Cluster_Webhook_Handler -- "indirectly supports" --> Core_Cluster_API_Controllers
    Machine_Webhook_Handler -- "operates on" --> Machine_CRD
    Machine_Webhook_Handler -- "indirectly supports" --> Core_Cluster_API_Controllers
    Core_Cluster_API_Controllers -- "consumes" --> Cluster_CRD
    Core_Cluster_API_Controllers -- "consumes" --> Machine_CRD
    click Core_Cluster_API_Controllers href "https://github.com/CodeBoarding/GeneratedOnBoardings/blob/main/cluster-api/Core_Cluster_API_Controllers.md" "Details"
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Details

The Cluster API webhook subsystem plays a crucial role in ensuring the integrity and correctness of Cluster and Machine resources within a Kubernetes cluster. The Kubernetes API Server acts as the central entry point, receiving all API requests. For Cluster API resources, the API Server invokes the Webhook Server/Manager, which is implemented using the controller-runtime framework. This Webhook Server/Manager is responsible for registering and routing admission requests to specific handlers. The Cluster Webhook Handler and Machine Webhook Handler are the core components that implement the actual admission logic, performing validation, mutation, and defaulting operations on Cluster CRD and Machine CRD objects, respectively. These handlers ensure that Cluster and Machine resources conform to defined policies and schemas before they are persisted in the Kubernetes datastore. The Core Cluster API Controllers then consume these validated Cluster and Machine CRDs to reconcile the desired state of the cluster infrastructure.

Webhook Server/Manager

Manages the lifecycle of webhook handlers, including listening for incoming admission requests from the Kubernetes API server, routing requests to the appropriate handler, and returning admission responses. It handles the registration of webhooks with the Kubernetes API server. This component leverages the controller-runtime Manager to orchestrate webhook operations.

Related Classes/Methods:

Cluster Webhook Handler

Implements admission logic (validation, mutation, defaulting) specifically for Cluster Custom Resources. It intercepts API requests for Cluster CRDs, enforces validation rules, and performs mutation/defaulting operations.

Related Classes/Methods:

Machine Webhook Handler

Implements admission logic (validation, mutation, defaulting) specifically for Machine Custom Resources. It intercepts API requests for Machine CRDs, enforces validation rules, and performs mutation/defaulting operations.

Related Classes/Methods:

Kubernetes API Server

The central control plane component in Kubernetes that exposes the Kubernetes API. It sends admission requests to registered webhooks and receives responses. This is an external component to the cluster-api project.

Related Classes/Methods: None

Cluster CRD

Custom Resource Definition for Cluster objects in Cluster API. These are the resources that the Cluster Webhook Handler validates, mutates, or defaults.

Related Classes/Methods:

Machine CRD

Custom Resource Definition for Machine objects in Cluster API. These are the resources that the Machine Webhook Handler validates, mutates, or defaults.

Related Classes/Methods:

Core Cluster API Controllers [Expand]

Controllers responsible for reconciling Cluster API resources. While not part of the webhook subsystem itself, they rely on the webhooks to ensure the validity and correctness of the resources they manage.

Related Classes/Methods:

FAQ