Service Catalog - Service Catalog Components | Architecture

Overview
Design
Concepts and Terminology
Provided Service Brokers

Overview

Enabling the service catalog is a Technology Preview feature only.

To opt-in during installation, see Advanced Installation.

When developing microservices-based applications to run on cloud native platforms, there are many ways to provision different resources and share their coordinates, credentials, and configuration, depending on the service provider and the platform.

To give developers a more seamless experience, OKD includes a service catalog, an implementation of the Open Service Broker API (OSB API) for Kubernetes. This allows users to connect any of their applications deployed in OKD to a wide variety of service brokers.

The service catalog allows cluster administrators to integrate multiple platforms using a single API specification. The OKD web console displays the service classes offered by brokers in the service catalog, allowing users to discover and instantiate those services for use with their applications.

As a result, service users benefit from ease and consistency of use across different types of services from different providers, while service providers benefit from having one integration point that gives them access to multiple platforms.

Design

The design of the service catalog follows this basic workflow:

New terms in the following are defined further in Concepts and Terminology.

1	A cluster administrator registers one or more service brokers with their OKD cluster. This can be done automatically during installation for some default-provided service brokers or manually.
2	Each service broker specifies a set of service classes and variations of those services (service plans) to OKD that should be made available to users.
3	Using the OKD web console or CLI, users discover the services that are available. For example, a service class may be available that is a database-as-a-service called BestDataBase.
4	A user chooses a service class and requests a new instance of their own. For example, a service instance may be a BestDataBase instance named `my_db`.
5	A user links, or binds, their service instance to a set of pods (their application). For example, the `my_db` service instance may be bound to the user’s application called `my_app`.

This infrastructure allows a loose coupling between applications running in OKD and the services they use. This allows the application that uses those services to focus on its own business logic while leaving the management of these services to the provider.

Concepts and Terminology

Service Broker

A service broker is a server that conforms to the OSB API specification and manages a set of one or more services. The software could be hosted within your own OKD cluster or elsewhere.

Cluster administrators can create Broker API resources representing service brokers and register them with their OKD cluster. This allows cluster administrators to make new types of managed services using that service broker available within their cluster.

A Broker resource specifies connection details for a service broker and the set of services (and variations of those services) to OKD that should then be made available to users.

Example Broker Resource

apiVersion: servicecatalog.k8s.io/v1alpha1
kind: Broker
metadata:
  name: BestCompanySaaS
spec:
  url: http://bestdatabase.example.com

Service Class

Also synonymous with "service" in the context of the service catalog, a service class is a type of managed service offered by a particular broker. Each time a new broker resource is added to the cluster, the service catalog controller connects to the corresponding service broker to obtain a list of service offerings. A new ServiceClass resource is automatically created for each.

OKD also has a core concept called services, which are separate Kubernetes resources related to internal load balancing. These resources are not to be confused with how the term is used in the context of the service catalog and OSB API.

Example ServiceClass Resource

apiVersion: servicecatalog.k8s.io/v1alpha1
kind: ServiceClass
metadata:
  name: smallDB
  brokerName: BestDataBase
  plans: [...]

Service Plan

A service plan is represents tiers of a service class. For example, a service class may expose a set of plans that offer varying degrees of quality-of-service (QoS), each with a different cost associated with it.

Service Instance

A service instance is a provisioned instance of a service class. When a user wants to use the capability provided by a service class, they can create a new instance.

When a new Instance resource is created, the service catalog controller connects to the appropriate service broker and instructs it to provision the service instance.

Example Instance Resource

apiVersion: servicecatalog.k8s.io/v1alpha1
kind: Instance
metadata:
  name: my_db
spec:
  serviceClassName: smallDB

Application

The term application refers to the OKD deployment artifacts, for example pods running in a user’s project, that will use a service instance.

Credentials

Credentials are information needed by an application to communicate with a service instance.

Service Binding

A service binding is a link between a service instance and an application. These are created by cluster users who wish for their applications to reference and use a service instance.

Upon creation, the service catalog controller creates a Kubernetes secret containing connection details and credentials for the service instance. Such secrets can be mounted into pods as usual. There is also integration with PodPresets, which allow you to express how the secret should be consumed, and in which pods.

Example Binding Resource

apiVersion: servicecatalog.k8s.io/v1alpha1
kind: Binding
metadata:
  name: myBinding
spec:
  secretName: mySecret
  <pod_selector_labels>

Provided Service Brokers

OKD provides the following service brokers for use with the service catalog.

Because the service catalog is currently Technology Preview, the provided service brokers are also currently Technology Preview.