#Creating applications from Operator Backed

#UnderStanding Operator Backed Application

An Operator is an extension mechanism built upon Kubernetes Custom Controllers and Custom Resource Definitions (CRDs), designed to automate the complete lifecycle management of complex applications. Within Alauda Container Platform, an Operator Backed Application refers to an application instance provisioned through pre-integrated or user-defined Operators, with its operational workflows managed by the Operator Lifecycle Manager (OLM). This encompasses critical processes such as installation, upgrades, dependency resolution, and access control.

#Core Capabilities

1. Automation of Complex Operations: Operators overcome the inherent limitations of native Kubernetes resources (e.g., Deployment, StatefulSet) to address the complexities of managing stateful applications, including distributed coordination, persistent storage, and versioned rolling updates. Example: Operator-encoded logic enables autonomous operations for database cluster failover, cross-node data consistency, and backup recovery.

2. Declarative, State-Driven Architecture: Operators utilize YAML-based declarative APIs to define desired application states (e.g., spec.replicas: 5). Operators continuously reconcile the actual state with the declared state, providing self-healing capabilities. Deep integration with GitOps tools (e.g., Argo CD) ensures consistent environment configurations.

3. Intelligent Lifecycle Management:

   • Rolling Updates & Rollback: OLM's Subscription object subscribes to update channels (e.g., stable, alpha), triggering automated version iterations for both Operators and their managed applications.

   • Dependency Resolution: Operators dynamically identify runtime dependencies (e.g., specific storage drivers, CNI plugins) to ensure successful deployment.

4. Standardized Ecosystem Integration: OLM standardizes Operator packaging (Bundle) and distribution channels, enabling one-click deployment of production-grade applications (e.g., Etcd) from OperatorHub or private registries. Enterprise Enhancements: Alauda Container Platform extends RBAC policies and multi-cluster distribution capabilities to meet enterprise compliance requirements.

#Operator Backed Application CRD

This Operator is designed and implemented by fully embracing open-source community standards and solutions. Its Custom Resource Definition (CRD) design thoughtfully incorporates established best practices and architectural patterns prevalent within the Kubernetes ecosystem. CRD design reference materials:

1. CatalogSource: Defines the source of Operator packages available to the cluster, such as OperatorHub or custom Operator repositories.

2. ClusterServiceVersion (CSV): The core metadata definition for an Operator, containing its name, version, provided APIs, required permissions, installation strategy, and detailed lifecycle management information.

3. InstallPlan: The actual execution plan for installing an Operator, automatically generated by OLM based on the Subscription and CSV, detailing the specific steps to create the Operator and its dependent resources.

4. OperatorGroup: Defines a set of target namespaces where an Operator will provide its services and reconcile resources, while also limiting the scope of the Operator's RBAC permissions.

5. Subscription: Used to declare the specific Operator that a user wants to install and track in the cluster, including the Operator's name, target channel (e.g., stable, alpha), and update strategy. OLM uses the Subscription to create and manage the Operator's installation and upgrades.

#Creating a Operator Backed Application by using web console

1. Container Platform, navigate to Applications > Applications in the left sidebar.

2. Click Create.

3. Choose Create from Catalog as the creation approach.

4. Select an Operator-Backed Instance and Configure Custom Resource Parameters. Select an Operator-managed application instance and configure its Custom Resource (CR) specifications in the CR manifest, including:

   • spec.resources.limits (container-level resource constraints).
   • spec.resourceQuota (Operator-defined quota policies). Other CR-specific parameters such as spec.replicas, spec.storage.className, etc.

5. Click Create.

The web console will navigate to Applications > Operator Backed Apps page.

#Troubleshooting

If resource creation fails:

1. Inspect controller reconciliation errors:

   kubectl get events --field-selector involvedObject.kind=<Your-Custom-Resource> --sort-by=.metadata.creationTimestamp
2. Verify API resource availability:

   kubectl api-resources | grep <Your-Resource-Type>
3. Retry creation after verifying CRD/Operator readiness:

   kubectl apply -f your-resource-manifest.yaml