Exposing binding data from a <strong>service</strong> - Connecting applications to <strong>service</strong>s | Building applications

Methods of exposing binding data
Data model
Setting annotations mapping to be optional
RBAC requirements
Categories of exposable binding data
Additional resources

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 requires a different way to access their secrets and consume them in a workload.

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. For the service Binding Operator to provide the binding data, as an Operator provider or user who creates backing services, you must expose the binding data to be automatically detected by the service Binding Operator. Then, the service Binding Operator automatically collects the binding data from the backing service and shares it with a workload to provide a consistent and predictable experience.

Methods of exposing binding data

This section describes the methods you can use to expose the binding data.

Ensure that you know and understand your workload requirements and environment, and how it works with the provided services.

Binding data is exposed under the following circumstances:

Backing service is available as a provisioned service resource.

The service you intend to connect to is compliant with the service Binding specification. You must create a Secret resource with all the required binding data values and reference it in the backing service custom resource (CR). The detection of all the binding data values is automatic.
Backing service is not available as a provisioned service resource.

You must expose the binding data from the backing service. Depending on your workload requirements and environment, you can choose any of the following methods to expose the binding data:
- Direct secret reference
- Declaring binding data through custom resource definition (CRD) or CR annotations
- Detection of binding data through owned resources

Provisioned service

Provisioned service represents a backing service CR with a reference to a Secret resource placed in the .status.binding.name field of the backing service CR.

As an Operator provider or the user who creates backing services, you can use this method to be compliant with the service Binding specification, by creating a Secret resource and referencing it in the .status.binding.name section of the backing service CR. This Secret resource must provide all the binding data values required for a workload to connect to the backing service.

The following examples show an Accountservice CR that represents a backing service and a Secret resource referenced from the CR.

Example: Accountservice CR

apiVersion: example.com/v1alpha1
kind: Accountservice
name: prod-account-service
spec:
# ...
status:
  binding:
    name: hippo-pguser-hippo

Example: Referenced Secret resource

apiVersion: v1
kind: Secret
metadata:
  name: hippo-pguser-hippo
data:
  password: "<password>"
  user: "<username>"
# ...

When creating a service binding resource, you can directly give the details of the Accountservice resource in the serviceBinding specification as follows:

Example: serviceBinding resource

apiVersion: binding.operators.coreos.com/v1alpha1
kind: serviceBinding
metadata:
  name: account-service
spec:
# ...
  services:
  - group: "example.com"
    version: v1alpha1
    kind: Accountservice
    name: prod-account-service
  application:
    name: spring-petclinic
    group: apps
    version: v1
    resource: deployments

Example: serviceBinding resource in Specification API

apiVersion: servicebinding.io/v1beta1
kind: serviceBinding
metadata:
  name: account-service
spec:
# ...
  service:
    apiVersion: example.com/v1alpha1
    kind: Accountservice
    name: prod-account-service
  workload:
    apiVersion: apps/v1
    kind: Deployment
    name: spring-petclinic

This method exposes all the keys in the hippo-pguser-hippo referenced Secret resource as binding data that is to be projected into the workload.

Direct secret reference

You can use this method, if all the required binding data values are available in a Secret resource that you can reference in your service Binding definition. In this method, a serviceBinding resource directly references a Secret resource to connect to a service. All the keys in the Secret resource are exposed as binding data.

Example: Specification with the binding.operators.coreos.com API

apiVersion: binding.operators.coreos.com/v1alpha1
kind: serviceBinding
metadata:
  name: account-service
spec:
# ...
  services:
  - group: ""
    version: v1
    kind: Secret
    name: hippo-pguser-hippo

Example: Specification that is compliant with the servicebinding.io API

apiVersion: servicebinding.io/v1beta1
kind: serviceBinding
metadata:
  name: account-service
spec:
# ...
  service:
    apiVersion: v1
    kind: Secret
    name: hippo-pguser-hippo

Declaring binding data through CRD or CR annotations

You can use this method to annotate the resources of the backing service to expose the binding data with specific annotations. Adding annotations under the metadata section alters the CRs and CRDs of the backing services. service Binding Operator detects the annotations added to the CRs and CRDs and then creates a Secret resource with the values extracted based on the annotations.

The following examples show the annotations that are added under the metadata section and a referenced ConfigMap object from a resource:

Example: Exposing binding data from a Secret object defined in the CR annotations

apiVersion: postgres-operator.crunchydata.com/v1beta1
kind: PostgresCluster
metadata:
  name: hippo
  namespace: my-petclinic
  annotations:
    service.binding: 'path={.metadata.name}-pguser-{.metadata.name},objectType=Secret'
# ...

The previous example places the name of the secret name in the {.metadata.name}-pguser-{.metadata.name} template that resolves to hippo-pguser-hippo. The template can contain multiple JSONPath expressions.

Example: Referenced Secret object from a resource

apiVersion: v1
kind: Secret
metadata:
  name: hippo-pguser-hippo
data:
  password: "<password>"
  user: "<username>"

Example: Exposing binding data from a ConfigMap object defined in the CR annotations

apiVersion: postgres-operator.crunchydata.com/v1beta1
kind: PostgresCluster
metadata:
  name: hippo
  namespace: my-petclinic
  annotations:
    service.binding: 'path={.metadata.name}-config,objectType=ConfigMap'
# ...

The previous example places the name of the config map in the {.metadata.name}-config template that resolves to hippo-config. The template can contain multiple JSONPath expressions.

Example: Referenced ConfigMap object from a resource

apiVersion: v1
kind: ConfigMap
metadata:
  name: hippo-config
data:
  db_timeout: "10s"
  user: "hippo"

Detection of binding data through owned resources

You can use this method if your backing service owns one or more Kubernetes resources such as route, service, config map, or secret that you can use to detect the binding data. In this method, the service Binding Operator detects the binding data from resources owned by the backing service CR.

The following examples show the detectBindingResources API option set to true in the serviceBinding CR:

Example

apiVersion: binding.operators.coreos.com/v1alpha1
kind: serviceBinding
metadata:
  name: spring-petclinic-detect-all
  namespace: my-petclinic
spec:
  detectBindingResources: true
  services:
    - group: postgres-operator.crunchydata.com
      version: v1beta1
      kind: PostgresCluster
      name: hippo
  application:
    name: spring-petclinic
    group: apps
    version: v1
    resource: deployments

In the previous example, PostgresCluster custom service resource owns one or more Kubernetes resources such as route, service, config map, or secret.

The service Binding Operator automatically detects the binding data exposed on each of the owned resources.

Data model

The data model used in the annotations follows specific conventions.

service binding annotations must use the following convention:

service.binding(/<NAME>)?:
    "<VALUE>|(path=<JSONPATH_TEMPLATE>(,objectType=<OBJECT_TYPE>)?(,elementType=<ELEMENT_TYPE>)?(,sourceKey=<SOURCE_KEY>)?(,sourceValue=<SOURCE_VALUE>)?)"

where:

`<NAME>`	Specifies the name under which the binding value is to be exposed. You can exclude it only when the `objectType` parameter is set to `Secret` or `ConfigMap`.
`<VALUE>`	Specifies the constant value exposed when no `path` is set.

The data model provides the details on the allowed values and semantic for the path, elementType, objectType, sourceKey, and sourceValue parameters.

Table 1. Parameters and their descriptions
Parameter	Description	Default value
`path`	JSONPath template that consists JSONPath expressions enclosed by curly braces {}.	N/A
`elementType`	Specifies whether the value of the element referenced in the `path` parameter complies with any one of the following types: `string` `sliceOfStrings` `sliceOfMaps`	`string`
`objectType`	Specifies whether the value of the element indicated in the `path` parameter refers to a `ConfigMap`, `Secret`, or plain string in the current namespace.	`Secret`, if `elementType` is non-string.
`sourceKey`	Specifies the key in the `ConfigMap` or `Secret` resource to be added to the binding secret when collecting the binding data. Note: When used in conjunction with `elementType`=`sliceOfMaps`, the `sourceKey` parameter specifies the key in the slice of maps whose value is used as a key in the binding secret. Use this optional parameter to expose a specific entry in the referenced `Secret` or `ConfigMap` resource as binding data. When not specified, all keys and values from the `Secret` or `ConfigMap` resource are exposed and are added to the binding secret.	N/A
`sourceValue`	Specifies the key in the slice of maps. Note: The value of this key is used as the base to generate the value of the entry for the key-value pair to be added to the binding secret. In addition, the value of the `sourceKey` is used as the key of the entry for the key-value pair to be added to the binding secret. It is mandatory only if `elementType`=`sliceOfMaps`.	N/A

The sourceKey and sourceValue parameters are applicable only if the element indicated in the path parameter refers to a ConfigMap or Secret resource.

Setting annotations mapping to be optional

You can have optional fields in the annotations. For example, a path to the credentials might not be present if the service endpoint does not require authentication. In such cases, a field might not exist in the target path of the annotations. As a result, service Binding Operator generates an error, by default.

As a service provider, to indicate whether you require annotations mapping, you can set a value for the optional flag in your annotations when enabling services. service Binding Operator provides annotations mapping only if the target path is available. When the target path is not available, the service Binding Operator skips the optional mapping and continues with the projection of the existing mappings without throwing any errors.

Procedure

To make a field in the annotations optional, set the optional flag value to true:

Example

apiVersion: apps.example.org/v1beta1
kind: Database
metadata:
  name: my-db
  namespace: my-petclinic
  annotations:
    service.binding/username: path={.spec.name},optional=true
# ...

If you set the optional flag value to false and the service Binding Operator is unable to find the target path, the Operator fails the annotations mapping.
If the optional flag has no value set, the service Binding Operator considers the value as false by default and fails the annotations mapping.

RBAC requirements

To expose the backing service binding data using the service Binding Operator, you require certain Role-based access control (RBAC) permissions. Specify certain verbs under the rules field of the ClusterRole resource to grant the RBAC permissions for the backing service resources. When you define these rules, you allow the service Binding Operator to read the binding data of the backing service resources throughout the cluster. If the users do not have permissions to read binding data or modify application resource, the service Binding Operator prevents such users to bind services to application. Adhering to the RBAC requirements avoids unnecessary permission elevation for the user and prevents access to unauthorized services or applications.

The service Binding Operator performs requests against the Kubernetes API using a dedicated service account. By default, this account has permissions to bind services to workloads, both represented by the following standard Kubernetes or OpenShift objects:

Deployments
DaemonSets
ReplicaSets
StatefulSets
DeploymentConfigs

The Operator service account is bound to an aggregated cluster role, allowing Operator providers or cluster administrators to enable binding custom service resources to workloads. To grant the required permissions within a ClusterRole, label it with the servicebinding.io/controller flag and set the flag value to true. The following example shows how to allow the service Binding Operator to get, watch, and list the custom resources (CRs) of Crunchy PostgreSQL Operator:

Example: Enable binding to PostgreSQL database instances provisioned by Crunchy PostgreSQL Operator

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: postgrescluster-reader
  labels:
     servicebinding.io/controller: "true"
rules:
- apiGroups:
    - postgres-operator.crunchydata.com
  resources:
    - postgresclusters
  verbs:
    - get
    - watch
    - list
  ...

This cluster role can be deployed during the installation of the backing service Operator.

Categories of exposable binding data

The service Binding Operator enables you to expose the binding data values from the backing service resources and custom resource definitions (CRDs).

This section provides examples to show how you can use the various categories of exposable binding data. You must modify these examples to suit your work environment and requirements.

Exposing a string from a resource

The following example shows how to expose the string from the metadata.name field of the PostgresCluster custom resource (CR) as a username:

Example

apiVersion: postgres-operator.crunchydata.com/v1beta1
kind: PostgresCluster
metadata:
  name: hippo
  namespace: my-petclinic
  annotations:
    service.binding/username: path={.metadata.name}
# ...

Exposing a constant value as the binding item

The following examples show how to expose a constant value from the PostgresCluster custom resource (CR):

Example: Exposing a constant value

apiVersion: postgres-operator.crunchydata.com/v1beta1
kind: PostgresCluster
metadata:
  name: hippo
  namespace: my-petclinic
  annotations:
    "service.binding/type": "postgresql" (1)

1	Binding `type` to be exposed with the `postgresql` value.

Exposing an entire config map or secret that is referenced from a resource

The following examples show how to expose an entire secret through annotations:

Example: Exposing an entire secret through annotations

apiVersion: postgres-operator.crunchydata.com/v1beta1
kind: PostgresCluster
metadata:
  name: hippo
  namespace: my-petclinic
  annotations:
    service.binding: 'path={.metadata.name}-pguser-{.metadata.name},objectType=Secret'

Example: The referenced secret from the backing service resource

apiVersion: v1
kind: Secret
metadata:
  name: hippo-pguser-hippo
data:
  password: "<password>"
  user: "<username>"

Exposing a specific entry from a config map or secret that is referenced from a resource

The following examples show how to expose a specific entry from a config map through annotations:

Example: Exposing an entry from a config map through annotations

apiVersion: postgres-operator.crunchydata.com/v1beta1
kind: PostgresCluster
metadata:
  name: hippo
  namespace: my-petclinic
  annotations:
    service.binding: 'path={.metadata.name}-config,objectType=ConfigMap,sourceKey=user'

Example: The referenced config map from the backing service resource

The binding data should have a key with name as db_timeout and value as 10s:

apiVersion: v1
kind: ConfigMap
metadata:
  name: hippo-config
data:
  db_timeout: "10s"
  user: "hippo"

Exposing a resource definition value

The following example shows how to expose a resource definition value through annotations:

Example: Exposing a resource definition value through annotations

apiVersion: postgres-operator.crunchydata.com/v1beta1
kind: PostgresCluster
metadata:
  name: hippo
  namespace: my-petclinic
  annotations:
    service.binding/username: path={.metadata.name}
    ...

Exposing entries of a collection with the key and value from each entry

The following example shows how to expose the entries of a collection with the key and value from each entry through annotations:

Example: Exposing the entries of a collection through annotations

apiVersion: postgres-operator.crunchydata.com/v1beta1
kind: PostgresCluster
metadata:
  name: hippo
  namespace: my-petclinic
  annotations:
    "service.binding/uri": "path={.status.connections},elementType=sliceOfMaps,sourceKey=type,sourceValue=url"
spec:
# ...
status:
  connections:
    - type: primary
      url: primary.example.com
    - type: secondary
      url: secondary.example.com
    - type: '404'
      url: black-hole.example.com

The following example shows how the previous entries of a collection in annotations are projected into the bound application.

Example: Binding data files

/bindings/<binding-name>/uri_primary => primary.example.com
/bindings/<binding-name>/uri_secondary => secondary.example.com
/bindings/<binding-name>/uri_404 => black-hole.example.com

Example: Configuration from a backing service resource

status:
  connections:
    - type: primary
      url: primary.example.com
    - type: secondary
      url: secondary.example.com
    - type: '404'
      url: black-hole.example.com

The previous example helps you to project all those values with keys such as primary, secondary, and so on.

Exposing items of a collection with one key per item

The following example shows how to expose the items of a collection with one key per item through annotations:

Example: Exposing the items of a collection through annotations

apiVersion: postgres-operator.crunchydata.com/v1beta1
kind: PostgresCluster
metadata:
  name: hippo
  namespace: my-petclinic
  annotations:
    "service.binding/tags": "path={.spec.tags},elementType=sliceOfStrings"
spec:
    tags:
      - knowledge
      - is
      - power

The following example shows how the previous items of a collection in annotations are projected into the bound application.

Example: Binding data files

/bindings/<binding-name>/tags_0 => knowledge
/bindings/<binding-name>/tags_1 => is
/bindings/<binding-name>/tags_2 => power

Example: Configuration from a backing service resource

spec:
  tags:
  - knowledge
  - is
  - power

Exposing values of collection entries with one key per entry value

The following example shows how to expose the values of collection entries with one key per entry value through annotations:

Example: Exposing the values of collection entries through annotations

apiVersion: postgres-operator.crunchydata.com/v1beta1
kind: PostgresCluster
metadata:
  name: hippo
  namespace: my-petclinic
  annotations:
    "service.binding/url": "path={.spec.connections},elementType=sliceOfStrings,sourceValue=url"
spec:
  connections:
    - type: primary
      url: primary.example.com
    - type: secondary
      url: secondary.example.com
    - type: '404'
      url: black-hole.example.com

The following example shows how the previous values of a collection in annotations are projected into the bound application.

Example: Binding data files

/bindings/<binding-name>/url_0 => primary.example.com
/bindings/<binding-name>/url_1 => secondary.example.com
/bindings/<binding-name>/url_2 => black-hole.example.com

Exposing binding data from a service

Methods of exposing binding data

Provisioned service

Direct secret reference

Declaring binding data through CRD or CR annotations

Detection of binding data through owned resources

Data model

Setting annotations mapping to be optional

RBAC requirements

Categories of exposable binding data

Exposing a string from a resource

Exposing a constant value as the binding item

Exposing an entire config map or secret that is referenced from a resource

Exposing a specific entry from a config map or secret that is referenced from a resource

Exposing a resource definition value

Exposing entries of a collection with the key and value from each entry

Exposing items of a collection with one key per item

Exposing values of collection entries with one key per entry value

Additional resources