FlagSourceConfigurations

FlagSourceConfiguration support multiple flag sources. Sources are configured as a list and given below are supported sources and their configurations,

kubernetes aka FeatureFlagConfiguration

This is FeatureFlagConfiguration custom resource backed flagd feature flag definition. Read more on the custom resource at the dedicated documentation of FeatureFlagConfiguration

To refer this custom resource in FlagSourceConfiguration, provider type kubernetes is used as below example,

sources:                        
  - source: flags/sample-flags  # FeatureFlagConfiguration - namespace/custom_resource_name
    provider: kubernetes        # kubernetes flag source backed by FeatureFlagConfiguration custom resource

flagd-proxy

flagd-proxy is an alternative to direct resource access on FeatureFlagConfiguration custom resources. This source type is useful when there is a need for restricting workload permissions and/or to reduce k8s API load.

Read more about proxy approach to access kubernetes resources: flagd-proxy

filepath

Injected sidecar can use volume mounted files as flag sources. For this, provider type filepath is used as below example,

sources:                        
  - source: /etc/flagd/config.json 
    provider: filepath          

http

Feature flags can be sources from a http endpoint using provider type http,

sources:
  - source: http://my-flag-source.json
    provider: http
    httpSyncBearerToken: token                  # optional bearer token for the http connection

grpc

Given below is an example configuration with provider type grpc and supported options,

sources:                        
  - source: my-flag-source:8080
    provider: grpc
    certPath: /certs/ca.cert                    # certificate for tls connectivity
    tls: true                                   # enforce tls connectivity
    providerID: flagd-weatherapp-sidecar        # identifier for this connection 
    selector: 'source=database,app=weatherapp'  # flag filtering options

Sidecar configurations

FlagSourceConfiguration further allows to provide configurations to the injected flagd sidecar. Table given below is non-exhaustive list of overriding options,

Configuration	Explanation	Default
port	Flag evaluation endpoint port	8013
metricsPort	Metrics port	8014
evaluator	Evaluator to use	json
image	flagD image	ghcr.io/open-feature/flagd
tag	flagD image tag	Latest tag
probesEnabled	Enable/Disable health probes	true

Merging of configurations

The annotation value is a comma separated list of values following one of two patterns: {NAME} or {NAMESPACE}/{NAME}. If no namespace is provided, it is assumed that the CR is within the same namespace as the deployed pod, for example:

    metadata:
        namespace: test-ns
        annotations:
            openfeature.dev/enabled: "true"
            openfeature.dev/flagsourceconfiguration: "config-A, test-ns-2/config-B"

In this example, 2 CRs are being used to configure the injected container (by default the operator uses the flagd:main image), config-A (which is assumed to be in the namespace test-ns) and config-B from the test-ns-2 namespace, with config-B taking precedence in the configuration merge.

The FlagSourceConfiguration version v1alpha3 CRD defines a CR with the following example structure, the documentation for this CRD can be found here:

apiVersion: core.openfeature.dev/v1alpha3
kind: FlagSourceConfiguration
metadata:
    name: flag-source-sample
spec:
    metricsPort: 8080
    Port: 80
    evaluator: json
    image: my-custom-sidecar-image
    defaultSyncProvider: filepath
    tag: main
    sources:
    - source: namespace/name
      provider: kubernetes
    - source: namespace/name2
    - source: not-a-real-host.com
      provider: http
    envVars:
    - name: MY_ENV_VAR
      value: my-env-value
    probesEnabled: true
    debugLogging: false

The relevant FlagSourceConfigurations are passed to the operator by setting the openfeature.dev/flagsourceconfiguration annotation, and is responsible for providing the full configuration of the injected sidecar.

Configuration Merging

When multiple FlagSourceConfigurations are provided, the configurations are merged. The last CR takes precedence over the first, with any configuration from the deprecated FlagDSpec field of the FeatureFlagConfiguration CRD taking the lowest priority.

flowchart LR
    FlagSourceConfiguration-values  -->|highest priority| environment-variables -->|lowest priority| defaults

An example of this behavior:

    metadata:
        annotations:
            openfeature.dev/enabled: "true"
            openfeature.dev/flagsourceconfiguration:"config-A, config-B"

Config-A:

apiVersion: core.openfeature.dev/v1alpha2
kind: FlagSourceConfiguration
metadata:
    name: config-A
spec:
    metricsPort: 8080
    tag: latest

Config-B:

apiVersion: core.openfeature.dev/v1alpha2
kind: FlagSourceConfiguration
metadata:
    name: config-B
spec:
    port: 8000
    tag: main

Results in the following configuration:

spec:
    metricsPort: 8080
    port: 8000
    tag: main