Controller Example

This example demonstrates how to use the generated clientset, informer, and lister to operate BatchSandbox and Pool custom resources.

Features

1. Clientset (Client Set)

Used to interact directly with the Kubernetes API Server for CRUD operations:

• Create: Create new resources
• Get: Retrieve specific resources
• List: List all resources
• Update: Update existing resources
• Delete: Delete resources

2. Informer (Informer)

Used to watch resource changes and maintain local cache:

• Automatically watches resource changes from the API Server
• Triggers event handlers (Add/Update/Delete)
• Maintains a local cache of resources to reduce API Server load

3. Lister (Lister)

Used to read resources from the Informer's local cache:

• High-performance local cache reads
• Avoids frequent API Server access
• Supports filtering by namespace and labels

Running the Example

Prerequisites

1. CRDs are installed in the Kubernetes cluster
2. Have a kubeconfig file to access the cluster

Install CRDs

# Run from project root directory
kubectl apply -f config/crd/bases/

Run the Example Program

# Use default kubeconfig (~/.kube/config)
go run examples/controller/main.go

# Or specify kubeconfig path
go run examples/controller/main.go -kubeconfig=/path/to/kubeconfig

Example Output

The program will perform the following operations:

1. Create Pool resource

   Successfully created Pool: example-pool

2. Get Pool resource

   Successfully retrieved Pool: example-pool, PoolMin: 2, PoolMax: 10

3. List all Pool resources

   Found 1 Pool(s):
     - example-pool (PoolMin: 2, PoolMax: 10)

4. Update Pool resource

   Successfully updated Pool: example-pool, new PoolMax: 20

5. Create BatchSandbox resource

   Successfully created BatchSandbox: example-batchsandbox, Replicas: 3

6. Get and update BatchSandbox

   Successfully updated BatchSandbox: example-batchsandbox, new Replicas: 5

7. Use Lister to read from cache

   Retrieved Pool from cache: example-pool, PoolMax: 20
   Found 1 BatchSandbox(es) from cache

8. Cleanup resources

   Successfully deleted BatchSandbox: example-batchsandbox
   Successfully deleted Pool: example-pool

Code Structure

main.go
├── Controller struct          # Controller structure
├── NewController()           # Create controller and register event handlers
├── DemonstrateClientsetUsage() # Demonstrate Clientset CRUD operations
└── DemonstrateListerUsage()   # Demonstrate Lister cache reads

Key Concepts

Clientset vs Lister

When to use Clientset:

• Need to create, update, or delete resources
• Need to get the latest state of resources
• Performing write operations

When to use Lister:

• Only need to read resources
• Can tolerate slight data staleness
• Need high-performance batch reads
• Want to reduce API Server load

Informer Event Handling

Informer triggers corresponding event handlers when resources change:

AddFunc: func(obj interface{}) {
    // Called when resource is created
}
UpdateFunc: func(old, new interface{}) {
    // Called when resource is updated
}
DeleteFunc: func(obj interface{}) {
    // Called when resource is deleted
}

Production Recommendations

1. Use Lister instead of frequent Clientset.Get() calls

   • Lister reads from local cache with better performance
   • Reduces pressure on the API Server

2. Properly handle Informer resync

   • Set a reasonable resync period (e.g., 30 seconds)
   • Use idempotent operations in event handlers

3. Use Workqueue to process events

   • Avoid time-consuming operations in event handlers
   • Use workqueue to implement retry mechanisms

4. Handle resource version conflicts

   • Use optimistic locking during Update operations
   • Catch Conflict errors and retry

Further Reading

• Kubernetes Client-go Documentation
• Writing Kubernetes Controllers
• Sample Controller

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This page is sourced from: kubernetes/examples/controller/README.md