component-architecture-basics

README

Operator Architecture Example

This directory contains an example of the architecture used in an operator. It demonstrates the two primary patterns: the Component Framework and Feature Mutations.

Running the Example

You can run this example directly using the Go toolchain:

go run examples/component-architecture-basics/main.go

The example will simulate four different reconciliation scenarios:

1. Legacy Version (7.9.0): Demonstrates "Cleanup" and "Legacy Compatibility" features.
2. Modern Version (8.1.0): Demonstrates "Tracing" and "Legacy Compatibility" features.
3. Future Version (9.0.0): Demonstrates "Tracing" enabled and "Legacy Compatibility" disabled.
4. Suspension: Demonstrates how the framework handles scaling down/suspending a component.

Example output:

$ go run examples/component-architecture-basics/main.go
=== Scenario 1: Reconciling Legacy Version 7.9.0 ===
2026-03-09T05:32:43Z    INFO    Deployment State        {"name": "example-legacy-web-ui"}
2026-03-09T05:32:43Z    INFO      Replicas      {"count": 1}
2026-03-09T05:32:43Z    INFO      Labels        {"labels": {"app.kubernetes.io/managed-by":"example-operator","app.kubernetes.io/name":"example-legacy-web-ui"}}
2026-03-09T05:32:43Z    INFO      Pod Labels    {"labels": {"app":"example-legacy-web-ui","app.kubernetes.io/managed-by":"example-operator","app.kubernetes.io/name":"example-legacy-web-ui"}}
2026-03-09T05:32:43Z    INFO      Container     {"name": "app"}
2026-03-09T05:32:43Z    INFO        Args        {"args": ["--legacy-mode"]}
2026-03-09T05:32:43Z    INFO        Env {"env": [{"name":"LOG_LEVEL","value":"info"},{"name":"DEPRECATED_SETTING","value":"legacy-value"}]}
Owner: example-legacy (Version: 7.9.0, Suspended: false)
  Condition WebInterfaceReady: False (Reason: Creating, Message: Waiting for replicas: 0/1 ready)

=== Scenario 2: Reconciling Modern Version 8.1.0 ===
2026-03-09T05:32:43Z    INFO    Deployment State        {"name": "example-modern-web-ui"}
2026-03-09T05:32:43Z    INFO      Replicas      {"count": 1}
2026-03-09T05:32:43Z    INFO      Labels        {"labels": {"app.kubernetes.io/managed-by":"example-operator","app.kubernetes.io/name":"example-modern-web-ui"}}
2026-03-09T05:32:43Z    INFO      Pod Labels    {"labels": {"app":"example-modern-web-ui","app.kubernetes.io/managed-by":"example-operator","app.kubernetes.io/name":"example-modern-web-ui"}}
2026-03-09T05:32:43Z    INFO      Container     {"name": "app"}
2026-03-09T05:32:43Z    INFO        Args        {"args": ["--legacy-mode"]}
2026-03-09T05:32:43Z    INFO        Env {"env": [{"name":"LOG_LEVEL","value":"info"},{"name":"NEW_MANDATORY_SETTING","value":"standard-value"}]}
Owner: example-modern (Version: 8.1.0, Suspended: false)
  Condition WebInterfaceReady: False (Reason: Creating, Message: Waiting for replicas: 0/1 ready)

=== Scenario 3: Reconciling Latest Version 9.0.0 ===
2026-03-09T05:32:43Z    INFO    Deployment State        {"name": "example-latest-web-ui"}
2026-03-09T05:32:43Z    INFO      Replicas      {"count": 1}
2026-03-09T05:32:43Z    INFO      Labels        {"labels": {"app.kubernetes.io/managed-by":"example-operator","app.kubernetes.io/name":"example-latest-web-ui"}}
2026-03-09T05:32:43Z    INFO      Pod Labels    {"labels": {"app":"example-latest-web-ui","app.kubernetes.io/managed-by":"example-operator","app.kubernetes.io/name":"example-latest-web-ui"}}
2026-03-09T05:32:43Z    INFO      Container     {"name": "app"}
2026-03-09T05:32:43Z    INFO        Args        {"args": []}
2026-03-09T05:32:43Z    INFO        Env {"env": [{"name":"LOG_LEVEL","value":"info"},{"name":"NEW_MANDATORY_SETTING","value":"standard-value"}]}
Owner: example-latest (Version: 9.0.0, Suspended: false)
  Condition WebInterfaceReady: False (Reason: Creating, Message: Waiting for replicas: 0/1 ready)

=== Scenario 4: Suspending the Component ===
Owner: example-latest (Version: 9.0.0, Suspended: true)
  Condition WebInterfaceReady: True (Reason: Suspended, Message: All resources are suspended.)

Directory Structure

• resources/: Custom resource wrappers for Kubernetes objects.
  • deployment_resource.go: Implements the framework's Resource, Alive, Suspendable, and DataExtractable interfaces for *appsv1.Deployment.
  • deployment_mutator.go: A "Planner-style" mutator for *appsv1.Deployment objects, allowing features to record intent without direct object manipulation.
  • deployment_builder.go: Configurable builder for the DeploymentResource.
  • deployment_construction.go: Factory for the core Deployment baseline configuration.
• features/: Version-aware feature gates and mutations using the framework's feature.Mutation type.
  • constraints.go: Example implementation of the feature.VersionConstraint interface using semver.
  • tracing_feature.go: Example feature: adds tracing configuration (version-gated).
  • legacy_compat_feature.go: Example feature: adds legacy compatibility flags (version-gated).
  • compatibility_cleanup_feature.go: Example feature: removes/replaces deprecated settings for older versions.
• exampleapp/: A mock application demonstrating the framework usage.
  • owner.go: A mock Custom Resource that implements the real component.OperatorCRD interface.
  • controller_example.go: A mock controller showing how to use the component.Builder and ReconcileContext.
• main.go: Entry point that demonstrates the assembly and usage of the components.

Key Concepts

Component Framework

The framework (pkg/component) groups related resources into a single logical unit. It centralizes:

• Reconciliation Flow: Standardized apply/delete/status logic.
• Status Aggregation: Computing a single "Ready" condition from multiple resources.
• Lifecycle Management: Handling suspension and "alive" checks consistently.

Feature Mutations

Instead of using complex if/else logic inside resource configuration, we use Feature Mutations:

• Baseline: A core, stable configuration for the resource (applied in Mutate(current client.Object)).
• Mutations: Small, focused functions that modify the resource if a feature is enabled.
• Planner-style Mutator: A restricted set of methods (DeploymentResourceMutator) that mutations use to record their intent. This avoids direct manipulation of the Kubernetes object by features and allows the mutator to resolve changes (like slice updates) efficiently in a single final pass.
• Registration: Mutations are registered through a builder and applied during the resource's Mutate(current client.Object) call.
• Application Process: The Mutate implementation follows a precise sequence:
  1. Core Baseline: Apply all desired fields from the core resource baseline to the current server object.
  2. Feature Mutations: Apply all registered feature mutations to the current object, allowing them to override or extend the baseline.
  3. State Sync: Update the internal desired state with the fully mutated current object. This ensures that subsequent calls to ConvergingStatus and ExtractData operate on the final, augmented state of the resource.

Resource Interface

The Resource interface in pkg/component is the central contract for all objects managed by the framework:

• Identity() string: Returns a unique identifier for the resource (e.g., apps/v1/Deployment/web-ui).
• Object() (client.Object, error): Returns a fresh copy of the baseline resource object before reconciliation. Returns the applied k8s object after reconciling.
• Mutate(current client.Object) error: Applies the core baseline, feature mutation intents, and any deferred mutations (like suspension) to the provided current server object. It also synchronizes the internal state to reflect these changes.

Documentation

Overview

Package main demonstrates the assembly and reconciliation of a Component-based application.