How Does the Kubernetes API Work? Demystifying the Inner Workings of the Kubernetes API

kubernetes api

The Kubernetes API serves as the backbone of the container orchestration platform, comprised of intricate components working seamlessly to handle user requests. In this exploration, we delve into the mechanics of storing resources into etcd, a critical aspect of the Kubernetes API.

Initiating Requests

When you input

 kubectl apply -f my.yaml

your YAML configuration is dispatched to the API, initiating a process that culminates in storing the information in etcd.

Initiating Requests  kubectl apply -f my.yaml

This command crystallizes the user’s intentions, setting in motion a cascade of processes within the API.

The HTTP Handler

Within the API, the HTTP handler acts as the initial responder, ensuring your access to the cluster is authenticated and authorized according to Role-Based Access Control (RBAC) rules.

The HTTP Handler

The HTTP handler serves as the initial line of defense for the API, acting as a crucial gatekeeper. It authenticates users and enforces authorization policies, ensuring that only legitimate and authorized requests proceed to subsequent processing stages.

Authentication and Authorization

The API validates your credentials, confirming your rights to create, delete, or list resources. This is where RBAC rules play a pivotal role in controlling user access.

Authentication and Authorization.

Mutation Admission Controller

Once authenticated, the request proceeds to the Mutation Admission Controller, responsible for modifying your YAML. For instance, it might add a default storage class if omitted.

Mutation Admission Controller

Schema Validation

The Schema Validation component examines the modified resource, ensuring its compliance with the internal schema. This step prevents the storage of malformed YAML in the cluster.

Schema Validation

Validation Admission Controller

The Validation Admission Controller steps in to halt the process if the resource violates predefined rules, such as attempting to deploy in a non-existent namespace or exceeding resource quotas.

Validation Admission Controller

Secure Resource Storage

Successfully passing through the Validation Admission Controller results in the secure storage of your resource in etcd, a pivotal achievement in the process.

Secure Resource Storage

Empowering Users

Users can register custom scripts with the Mutating Admission Controller, allowing for personalized modifications to resources before they reach etcd. This empowers users to design checks for resource validation.

Empowering Users

Custom Admission Controllers

Users can design their custom admission controllers, exemplified by tools like Istio, which automatically injects containers into all Pods (mutation), and Gatekeeper (Open Policy Agent), which validates resources against policies.

Custom Admission Controllers


Understanding the inner workings of the Kubernetes API, particularly the journey of resource storage into etcd, provides users with insights into the robust mechanisms ensuring the security, validity, and integrity of deployed resources. This knowledge empowers users to tailor their Kubernetes experience and design custom processes through admission controllers.

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What is the Kubernetes API, and why is it crucial?

The Kubernetes API is the primary interface for managing containerized applications. It orchestrates resources and ensures the desired state of a cluster. Its significance lies in providing a unified point of control for users.

How does the Kubernetes API handle resource deployment in a cluster?

Users interact with the API by submitting configurations through tools like kubectl apply. The API processes these requests, ensuring authentication, validation, and the secure storage of configurations in the etcd datastore.

What authentication methods does the Kubernetes API support?

Kubernetes supports various authentication mechanisms, including token-based authentication and certificate-based authentication. These methods enhance security by verifying the identity of users interacting with the cluster.

How does Role-Based Access Control (RBAC) contribute to the security of the Kubernetes API?

RBAC in Kubernetes ensures that users and components have well-defined permissions, preventing unauthorized access and maintaining the security of the cluster.

Can users customize the behavior of the Kubernetes API?

Yes, users can customize the behavior of the API by implementing custom admission controllers. These controllers allow users to enforce specific policies and modify resource configurations before they are stored in the cluster.

What role does Schema Validation play in the Kubernetes API?

Schema Validation ensures that submitted YAML configurations conform to predefined structures, preventing misconfigurations and maintaining the integrity of the cluster.

How does the Kubernetes API handle namespace validation and resource quotas?

The Validation Admission Controller within the API enforces rules such as namespace validation and resource quotas, ensuring compliance with policies and maintaining stability in the cluster.

Can users extend the Kubernetes API with custom resources?

Yes, users can extend the API by defining custom resources using Custom Resource Definitions (CRDs). This feature allows the API to support unique application requirements and use cases.

How does the Kubernetes API support versioning and compatibility?

The Kubernetes API is versioned, allowing for smooth upgrades and ensuring backward compatibility. This ensures a seamless transition for users adopting new features or migrating to newer Kubernetes releases.

Are there examples of custom admission controllers in the Kubernetes ecosystem?

Yes, notable examples include Istio, which automates container injection into Pods (mutation), and Gatekeeper (Open Policy Agent), which validates resources against policies. These examples showcase the extensibility and versatility of custom admission controllers in enhancing Kubernetes functionality.
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