Advanced Features in client-go

Beyond basic interactions, client-go offers advanced features for specific use cases.

Dynamic Resource Access:

• The dynamic package allows for generic operations on arbitrary Kubernetes API objects, including custom resources. README.md
• Example: The dynamic-create-update-delete-deployment example demonstrates fundamental operations for managing Deployment resources using the dynamic package.

Scaling and Performance:

• The informer framework provides a mechanism for efficiently watching resources and keeping local caches synchronized with the Kubernetes cluster. informer
• Work queues are used to build hotloop-free controllers that handle events efficiently. examples/README.md

High Availability (HA) Controllers:

• The leader election package provides a mechanism for ensuring that only one instance of a controller is active at a time. This is crucial for HA deployments. examples/README.md

Custom Resource Definitions (CRDs):

• Client-go supports registering and managing custom resource types. examples/README.md

Feature Gates:

• The features package allows for controlling the behavior of client-go based on feature flags. features/features.go
• Features can be enabled or disabled using environment variables or through direct configuration. features/envvar.go
• Known features are listed in features/known_features.go.

Example:

// Enable a feature gate
          import "k8s.io/client-go/features"
          
          features.Set("MyFeature", true) 
          

Testing Feature Gates:

• The testing sub-package provides facilities for overriding feature gates during testing. features/testing/features.go

Example:

import "k8s.io/client-go/features/testing"
          
          func TestFeatureGate(t *testing.T) {
              // Create a fake feature gates instance
              fakeGates := &testing.FakeFeatureGates{
                  Features: map[features.Feature]bool{
                      "MyFeature": true,
                  },
              }
              // Override the default feature gates
              features.SetFakeFeatureGates(fakeGates)
          
              // ... Run your test code ...
          }
          

Top-Level Directory Explanations

applyconfigurations/ - This directory contains examples and tests for applying Kubernetes configurations using the client-go library.

discovery/ - This directory contains code related to service discovery in Kubernetes.

dynamic/ - This directory contains code for working with dynamic resources in the Kubernetes API.

features/ - This directory contains experimental features that are not yet stable.

gentype/ - This directory contains generated Go types for the Kubernetes API.

informers/ - This directory contains code for caching Kubernetes resources using informers.

kubernetes/ - This directory contains the main package for the client-go library, which provides types and functions for interacting with the Kubernetes API.

listers/ - This directory contains interfaces and implementations for listing Kubernetes resources.

metadata/ - This directory contains code related to metadata in Kubernetes.

openapi/ - This directory contains OpenAPI definitions for the Kubernetes API.

pkg/ - This directory contains compiled Go packages for the client-go library.

plugin/ - This directory contains code for loading plugins for the client-go library.

rest/ - This directory contains code for working with the REST API in the client-go library.

scale/ - This directory contains code for working with scale and autoscaling in Kubernetes.

tools/ - This directory contains various tools for working with the client-go library.

util/ - This directory contains utility functions for the client-go library.