Feature Flags Reference#

SDK parameters, API endpoints, environment variables, and external documentation.

External documentation#

GitLab Feature Flags#

Unleash (Open Source)#

Client SDKs#

Note

Use SDK v5.0 — GitLab does not yet support v6.

GitLab API endpoints#

Use these endpoints for programmatic flag management (e.g., via CI/CD):

Action	Endpoint
List feature flags	GET /projects/:id/feature_flags
Create a feature flag	POST /projects/:id/feature_flags
Update a strategy	PUT /projects/:id/feature_flags/:name/strategies/:id
Delete a feature flag	DELETE /projects/:id/feature_flags/:name

Environment variables#

Unleash Python SDK#

Variable	Description	Default
`UNLEASH_URL`	Unleash API server URL	Required
`UNLEASH_APP_NAME`	Application identifier	Required
`UNLEASH_INSTANCE_ID`	Unique instance identifier	Required
`UNLEASH_ENVIRONMENT`	Runtime environment	`development`
`UNLEASH_REFRESH_INTERVAL`	Flag refresh interval (seconds)	`15`
`UNLEASH_METRICS_INTERVAL`	Metrics send interval (seconds)	`60`
`UNLEASH_INACTIVE`	Disable client entirely	Not set

Unleash Proxy#

Variable	Description
`UNLEASH_PROXY_SECRETS`	Shared secret for Unleash Proxy client
`UNLEASH_URL`	Project’s API URL
`UNLEASH_INSTANCE_ID`	Project’s Instance ID
`UNLEASH_APP_NAME`	Application environment name
`UNLEASH_API_TOKEN`	Starts the Proxy (GitLab accepts any value)

React Proxy Client#

Variable	Description	Default
`REACT_APP_UNLEASH_PROXY_URL`	Unleash Proxy URL	Required
`REACT_APP_UNLEASH_APP_NAME`	Application name	Required
`REACT_APP_UNLEASH_ENVIRONMENT`	Runtime environment	`development`
`REACT_APP_UNLEASH_CLIENT_KEY`	Proxy client key (if required)	Empty
`REACT_APP_UNLEASH_REFRESH_INTERVAL`	Refresh interval (seconds)	`30`
`REACT_APP_UNLEASH_DISABLE_METRICS`	Disable metrics	`false`

Python SDK reference#

Installation#

pip install UnleashClient

Initialisation#

from UnleashClient import UnleashClient

client = UnleashClient(
    url="http://gitlab.com/api/v4/feature_flags/unleash/<PROJECT_ID>",
    app_name="my-python-app",
    custom_headers={'Authorization': '<API token>'}
)

client.initialize_client()

Parameters#

Parameter	Description
`url`	Unleash server URL
`app_name`	Application identifier
`custom_headers`	Headers for authentication
`environment`	Runtime environment
`instance_id`	Unique instance identifier
`refresh_interval`	Toggle refresh timing (seconds)
`metrics_interval`	Metrics sending timing (seconds)
`disable_metrics`	Turn off metrics
`disable_registration`	Skip server registration
`cache_directory`	Local cache location

Check flag status#

# Simple check
is_enabled = client.is_enabled("my_toggle")

# With context
context = {"userId": "user@example.com"}
is_enabled = client.is_enabled("user_toggle", context)

# With fallback
is_enabled = client.is_enabled(
    "my_toggle",
    fallback_function=lambda: False
)

Get variant#

context = {'userId': '2'}
variant = client.get_variant("variant_toggle", context)

Context fields#

userId — User identifier
sessionId — Session identifier
remoteAddress — IP address
properties — Custom properties dictionary

Supported strategies#

Default
UserID
IP
Gradual Rollout
Flexible Rollout

React Proxy Client reference#

Warning

Use only with the Unleash Proxy, not the Unleash client directly. This protects server-side API tokens.

Installation#

npm install @unleash/proxy-client-react

Initialisation#

import { UnleashClient } from 'unleash-proxy-client';

const unleash = new UnleashClient({
  url: 'https://YOUR-PROXY/api/frontend',
  clientKey: '<your-client-side-token>',
  appName: 'my-webapp'
});

unleash.start();

Parameters#

Parameter	Description
`url`	Front-end API or Edge URL
`clientKey`	Client-side API token
`appName`	Application identifier
`context`	Initial Unleash context
`refreshInterval`	Toggle refresh timing (seconds)
`disableRefresh`	Turn off auto-refresh
`metricsInterval`	Metrics sending timing (seconds)
`disableMetrics`	Turn off metrics
`storageProvider`	Custom storage implementation
`bootstrap`	Initial toggle configuration
`environment`	Context environment property

React hooks#

import { useFlag, useVariant, useFlags, useUnleashContext } from '@unleash/proxy-client-react';

// Check single flag
const isEnabled = useFlag('my-flag');

// Get variant
const variant = useVariant('my-flag');

// Check multiple flags
const flags = useFlags(['flag-one', 'flag-two']);

// Update context
const updateContext = useUnleashContext();
updateContext({ userId: '123' });

Events#

unleash.on('ready', () => {
  // Client connected to API
});

unleash.on('update', () => {
  // New toggle configuration received
});

unleash.on('error', (error) => {
  // Handle error
});

Available events:

initialized — SDK reads local cached data
ready — SDK connects to Unleash API
update — SDK receives new toggle configuration
error — SDK encounters an error
recovered — SDK recovers from error
sent — SDK sends metrics

Cleanup#

unleash.stop();