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This code demonstrates how to use the resource package from Cilium’s Kubernetes integration to observe and process changes in Pods and Services. It shows how to use the Store and Events functions to retrieve data and subscribe to events, respectively.

Here’s a breakdown of the code:

• Hive:

• The code leverages the hive package for dependency injection and modularity.

• client.Cell: This provides the Kubernetes clientset for accessing the Kubernetes API.

• resourcesCell: A cell that provides instances of resource.Resource for both Pods and Services.

• printServicesCell: A cell that creates an instance of the PrintServices type.

• resourcesCell:

• This cell uses the Kubernetes client to create resource.Resource instances for Pods and Services.

• It uses a utils.ListerWatcher to watch for changes to Pods and Services in the Kubernetes API.

• The resource.New function initializes the resource.Resource instances with the lister-watcher and an optional metric name (“Pod” or “Service”).

• printServicesCell:

• It defines the PrintServices struct, which is responsible for observing and processing changes in Pods and Services.

• The newPrintServices function creates an instance of PrintServices and provides the necessary dependencies.

• PrintServices struct:

• It contains a worker pool to process the event loop and holds references to the resource.Resource instances for Pods and Services.

• Start function:

• Initializes the worker pool and starts the processLoop.

• It does a blocking dump of all services using the Store function to demonstrate initial data retrieval.

• Stop function:

• Closes the worker pool to stop the event loop.

• printServices function:

• Retrieves a handle to the store of Services and prints the services and their selectors.

• processLoop function:

• Contains the event loop logic.

• Subscribes to events from both Pods and Services using the Events function.

• Keeps track of Pod labels and Service selectors in maps.

• Periodically prints the services and the Pods that they select.

• Handles events from the Events channel:

• Sync: Indicates the initial sync has completed.

• Upsert: Represents an update or creation of a Pod or Service.

• Delete: Represents a deletion of a Pod or Service.

• Includes a simulated fault to demonstrate error handling.

Key Concepts:

• resource.Resource: A type that provides a convenient way to interact with Kubernetes resources. It allows retrieving a store (for retrieving all objects) and subscribing to events.
• Store: Provides access to a snapshot of the Kubernetes resources.
• Events: Returns a channel that emits events when Kubernetes resources change.
• Event Kinds: Sync, Upsert, and Delete represent the different types of events that can occur.
• Worker Pool: Used for managing the event loop to process events efficiently.

Overall, this code provides a basic example of how to use the resource package to observe Kubernetes resources and process their changes.