Instances

Once kro processes your ResourceGroup, it creates a new API in your cluster. Users can then create instances of this API to deploy resources in a consistent, controlled way.

Understanding Instances

An instance represents your deployed application. When you create an instance, you're telling kro "I want this set of resources running in my cluster". The instance contains your configuration values and serves as the single source of truth for your application's desired state. Here's an example instance of our WebApplication API:

apiVersion: v1alpha1
kind: WebApplication
metadata:
  name: my-app
spec:
  name: web-app
  image: nginx:latest
  ingress:
    enabled: true

When you create this instance, kro:

• Creates all required resources (Deployment, Service, Ingress)
• Configures them according to your specification
• Manages them as a single unit
• Keeps their status up to date

How kro Manages Instances

kro uses the standard Kubernetes reconciliation pattern to manage instances:

1. Observe: Watches for changes to your instance or its resources
2. Compare: Checks if current state matches desired state
3. Act: Creates, updates, or deletes resources as needed
4. Report: Updates status to reflect current state

This continuous loop ensures your resources stay in sync with your desired state, providing features like:

• Self-healing
• Automatic updates
• Consistent state management
• Status tracking

Monitoring Your Instances

KRO provides rich status information for every instance:

$ kubectl get webapplication my-app
NAME     STATUS    SYNCED   AGE
my-app   ACTIVE    true     30s

For detailed status, check the instance's YAML:

status:
  state: ACTIVE # High-level instance state
  availableReplicas: 3 # Status from Deployment
  conditions: # Detailed status conditions
    - type: Ready
      status: "True"
      lastTransitionTime: "2024-07-23T01:01:59Z"
      reason: ResourcesAvailable
      message: "All resources are available and configured correctly"

Understanding Status

Every instance includes:

1. State: High-level status

   • Running: All resources are ready
   • Progressing: Working towards desired state
   • Failed: Error occurred
   • Terminating: Being deleted

2. Conditions: Detailed status information

   • Ready: Instance is fully operational
   • Progressing: Changes are being applied
   • Degraded: Operating but not optimal
   • Error: Problems detected

3. Resource Status: Status from your resources

   • Values you defined in your ResourceGroup's status section
   • Automatically updated as resources change

Best Practices

• Version Control: Keep your instance definitions in version control alongside your application code. This helps track changes, rollback when needed, and maintain configuration history.

• Use Labels Effectively: Add meaningful labels to your instances for better organization, filtering, and integration with other tools. kro propagates labels to the sub resources for easy identification.

• Active Monitoring: Regularly check instance status beyond just "Running". Watch conditions, resource status, and events to catch potential issues early and understand your application's health.

• Regular Reviews: Periodically review your instance configurations to ensure they reflect current requirements and best practices. Update resource requests, limits, and other configurations as your application needs evolve.