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featureflagsource.md

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FeatureFlagSources

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

kubernetes aka FeatureFlag

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

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

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

flagd-proxy

flagd-proxy is an alternative to direct resource access on FeatureFlag 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

FeatureFlagSource 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/featureflagsource: "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 FeatureFlagSource 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: FeatureFlagSource
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 FeatureFlagSources are passed to the operator by setting the openfeature.dev/featureflagsource annotation, and is responsible for providing the full configuration of the injected sidecar.

Configuration Merging

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

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

An example of this behavior:

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

Config-A:

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

Config-B:

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

Results in the following configuration:

spec:
    metricsPort: 8080
    port: 8000
    tag: main