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Understanding Service Binding Operator - Connecting applications to services | Building applications | OKD 4.10
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Understanding Service Binding Operator

Application developers need access to backing services to build and connect workloads. Connecting workloads to backing services is always a challenge because each service provider suggests a different way to access their secrets and consume them in a workload. In addition, manual configuration and maintenance of this binding together of workloads and backing services make the process tedious, inefficient, and error-prone.

The Service Binding Operator enables application developers to easily bind workloads together with Operator-managed backing services, without any manual procedures to configure the binding connection.

Service Binding terminology

This section summarizes the basic terms used in Service Binding.

Service binding

The representation of the action of providing information about a service to a workload. Examples include establishing the exchange of credentials between a Java application and a database that it requires.
Backing service

Any service or software that the application consumes over the network as part of its normal operation. Examples include a database, a message broker, an application with REST endpoints, an event stream, an Application Performance Monitor (APM), or a Hardware Security Module (HSM).
Workload (application)

Any process running within a container. Examples include a Spring Boot application, a NodeJS Express application, or a Ruby on Rails application.
Binding data

Information about a service that you use to configure the behavior of other resources within the cluster. Examples include credentials, connection details, volume mounts, or secrets.
Binding connection

Any connection that establishes an interaction between the connected components, such as a bindable backing service and an application requiring that backing service.

About Service Binding Operator

The Service Binding Operator consists of a controller and an accompanying custom resource definition (CRD) for service binding. It manages the data plane for workloads and backing services. The Service Binding Controller reads the data made available by the control plane of backing services. Then, it projects this data to workloads according to the rules specified through the ServiceBinding resource.

As a result, the Service Binding Operator enables workloads to use backing services or external services by automatically collecting and sharing binding data with the workloads. The process involves making the backing service bindable and binding the workload and the service together.

Making an Operator-managed backing service bindable

To make a service bindable, as an Operator provider, you need to expose the binding data required by workloads to bind with the services provided by the Operator. You can provide the binding data either as annotations or as descriptors in the CRD of the Operator that manages the backing service.

Binding a workload together with a backing service

By using the Service Binding Operator, as an application developer, you need to declare the intent of establishing a binding connection. You must create a ServiceBinding CR that references the backing service. This action triggers the Service Binding Operator to project the exposed binding data into the workload. The Service Binding Operator receives the declared intent and binds the workload together with the backing service.

The CRD of the Service Binding Operator supports the following APIs:

  • Service Binding with the binding.operators.coreos.com API group.

  • Service Binding (Spec API) with the servicebinding.io API group.

With Service Binding Operator, you can:

  • Bind your workloads to Operator-managed backing services.

  • Automate configuration of binding data.

  • Provide service operators with a low-touch administrative experience to provision and manage access to services.

  • Enrich the development lifecycle with a consistent and declarative service binding method that eliminates discrepancies in cluster environments.

Key features

  • Exposal of binding data from services

    • Based on annotations present in CRD, custom resources (CRs), or resources.

  • Workload projection

    • Projection of binding data as files, with volume mounts.

    • Projection of binding data as environment variables.

  • Service Binding Options

    • Bind backing services in a namespace that is different from the workload namespace.

    • Project binding data into the specific container workloads.

    • Auto-detection of the binding data from resources owned by the backing service CR.

    • Compose custom binding data from the exposed binding data.

    • Support for non-PodSpec compliant workload resources.

  • Security

    • Support for role-based access control (rbac).

API differences

The CRD of the Service Binding Operator supports the following APIs:

  • Service Binding with the binding.operators.coreos.com API group.

  • Service Binding (Spec API) with the servicebinding.io API group.

Both of these API groups have similar features, but they are not completely identical. Here is the complete list of differences between these API groups:

Feature Supported by the binding.operators.coreos.com API group Supported by the servicebinding.io API group Notes

Binding to provisioned services

Yes

Yes

Not applicable (N/A)

Direct secret projection

Yes

Yes

Not applicable (N/A)

Bind as files

Yes

Yes

  • Default behavior for the service bindings of the servicebinding.io API group

  • Opt-in functionality for the service bindings of the binding.operators.coreos.com API group

Bind as environment variables

Yes

Yes

  • Default behavior for the service bindings of the binding.operators.coreos.com API group.

  • Opt-in functionality for the service bindings of the servicebinding.io API group: Environment variables are created alongside files.

Selecting workload with a label selector

Yes

Yes

Not applicable (N/A)

Detecting binding resources (.spec.detectBindingResources)

Yes

No

The servicebinding.io API group has no equivalent feature.

Naming strategies

Yes

No

There is no current mechanism within the servicebinding.io API group to interpret the templates that naming strategies use.

Container path

Yes

Partial

Because a service binding of the binding.operators.coreos.com API group can specify mapping behavior within the ServiceBinding resource, the servicebinding.io API group cannot fully support an equivalent behavior without more information about the workload.

Container name filtering

No

Yes

The binding.operators.coreos.com API group has no equivalent feature.

Secret path

Yes

No

The servicebinding.io API group has no equivalent feature.

Alternative binding sources (for example, binding data from annotations)

Yes

Allowed by Service Binding Operator

The specification requires support for getting binding data from provisioned services and secrets. However, a strict reading of the specification suggests that support for other binding data sources is allowed. Using this fact, Service Binding Operator can pull the binding data from various sources (for example, pulling binding data from annotations). Service Binding Operator supports these sources on both the API groups.

Additional resources