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Configuring Unleash

This is the guide on how to configure Unleash v4 self-hosted. If you are still using Unleash v3 you should checkout configuring Unleash v3

Must configure#

Database details#

In order for Unleash server to work, you must setup database connection details.

  • If using docker, use environment variables
    • DATABASE_HOST - the database hostname - defaults to localhost
    • DATABASE_PORT - the port the database is listening on - defaults to 5432
    • DATABASE_USERNAME - the user configured for access - defaults to unleash_user
    • DATABASE_PASSWORD - the password for the user - defaults to passord
    • DATABASE_NAME - the name of the database - defaults to unleash
    • DATABASE_SSL - a json object representing SSL configuration or false for not using SSL
    • DATABASE_SCHEMA - Which schema to use - defaults to public
  • We also support DATABASE_URL see libpq's doc for full format explanation. In short: postgres://USER:PASSWORD@HOST:PORT/DATABASE
  • If you're using secret files from kubernetes and would like to load a DATABASE_URL format from a file, use DATABASE_URL_FILE and point it to a path containing a connection URL.

Nice to configure#

Unleash URL#

  • Configured with UNLEASH_URL Should be set to the public discoverable URL of your instance, so if your instance is accessed by your users at use that. If you're deploying this to a subpath, include the subpath in this. So will also be correct.
  • Used to create
    • Reset password URLs
    • Welcome link for new users
    • Links in events for our Slack, Microsoft Teams and Datadog addons

Email server details#

Used to send reset-password mails and welcome mails when onboarding new users.
NOTE - If this is not configured, you will not be able to allow your users to reset their own passwords.

For more details, see here

Further customization#

In order to customize "anything" in Unleash you need to use Unleash from Node.js or start the docker image with environment variables.

const unleash = require('unleash-server');
const unleashOptions = {
db: {
user: 'unleash_user',
password: 'passord',
host: 'localhost',
port: 5432,
database: 'unleash',
ssl: false,
pool: {
min: 0,
max: 4,
idleTimeoutMillis: 30000,
enableRequestLogger: true,

Available Unleash options include:

  • databaseUrl - (deprecated) the postgres database url to connect to. Only used if db object is not specified, and overrides the db object and any environment variables that change parts of it (like DATABASE_SSL). Should include username/password. This value may also be set via the DATABASE_URL environment variable. Alternatively, if you would like to read the database url from a file, you may set the DATABASE_URL_FILE environment variable with the full file path. The contents of the file must be the database url exactly.
  • db - The database configuration object taking the following properties:
    • user - the database username (DATABASE_USERNAME)
    • password - the database password (DATABASE_PASSWORD)
    • host - the database hostname (DATABASE_HOST)
    • port - the database port defaults to 5432 (DATABASE_PORT)
    • database - the database name to be used (DATABASE_NAME)
    • ssl - an object describing ssl options, see (DATABASE_SSL, as a stringified json object)
    • schema - the postgres database schema to use. Defaults to 'public'. (DATABASE_SCHEMA)
    • version - the postgres database version. Used to connect a non-standard database. Defaults to undefined, which let the underlying adapter to detect the version automatically. (DATABASE_VERSION)
    • pool - an object describing pool options, see We support the following three fields:
      • min - minimum connections in connections pool (defaults to 0) (DATABASE_POOL_MIN)
      • max - maximum connections in connections pool (defaults to 4) (DATABASE_POOL_MAX)
      • idleTimeoutMillis - time in milliseconds a connection must be idle before being marked as a candidate for eviction (defaults to 30000) (DATABASE_POOL_IDLE_TIMEOUT_MS)
  • server - The server config object taking the following properties
    • port - which port the unleash-server should bind to. If port is omitted or is 0, the operating system will assign an arbitrary unused port. Will be ignored if pipe is specified. This value may also be set via the HTTP_PORT environment variable
    • host - which host the unleash-server should bind to. If host is omitted, the server will accept connections on the unspecified IPv6 address (::) when IPv6 is available, or the unspecified IPv4 address ( otherwise. This value may also be set via the HTTP_HOST environment variable
    • pipe - parameter to identify IPC endpoints. See for more details
    • serverMetrics (boolean) - use this option to turn on/off prometheus metrics.
    • baseUriPath (string) - use to register a base path for all routes on the application. For example /my/unleash/base (note the starting /). Defaults to /. Can also be configured through the environment variable BASE_URI_PATH.
    • unleashUrl (string) - Used to specify the official URL this instance of Unleash can be accessed at for an end user. Can also be configured through the environment variable UNLEASH_URL.
    • _gracefulShutdownEnable: (boolean) - Used to control if Unleash should shutdown gracefully (close connections, stop tasks,). Defaults to true. GRACEFUL_SHUTDOWN_ENABLE
    • _gracefulShutdownTimeout: (number) - Used to control the timeout, in milliseconds, for shutdown Unleash gracefully. Will kill all connections regardless if this timeout is exceeded. Defaults to 1000ms GRACEFUL_SHUTDOWN_TIMEOUT
  • preHook (function) - this is a hook if you need to provide any middlewares to express before unleash adds any. Express app instance is injected as first argument.
  • preRouterHook (function) - use this to register custom express middlewares before the unleash specific routers are added.
  • authentication - (object) - An object for configuring/implementing custom admin authentication
    • enableApiToken (boolean) - Should unleash require API tokens for access? Defaults to true
    • type (string) What kind of authentication to use. Possible values
      • open-source -
      • custom - If implementing your own authentication hook, use this
      • none - Turn off authentication all together
      • demo - Only requires an email to sign-in (was default in v3)
    • customAuthHandler: (function) - custom express middleware handling authentication. Used when type is set to custom
    • createAdminUser: (boolean) - whether to create an admin user with default password - Defaults to true
  • ui (object) - Set of UI specific overrides. You may set the following keys: headerBackground, environment, slogan.
  • getLogger (function) - Used to register a custom log provider.
  • logLevel (debug | info | warn | error | fatal) - The lowest level to log at, also configurable using environment variable LOG_LEVEL.
  • eventHook (function(event, data)) - If provided, this function will be invoked whenever a feature is mutated. The possible values for event are 'feature-created', 'feature-updated', 'feature-archived', 'feature-revived'. The data argument contains information about the mutation. Its fields are type (string) - the event type (same as event); createdBy (string) - the user who performed the mutation; data - the contents of the change. The contents in data differs based on the event type; For 'feature-archived' and 'feature-revived', the only field will be name - the name of the feature. For 'feature-created' and 'feature-updated' the data follows a schema defined in the code here. See an api here.
  • secureHeaders (boolean) - use this to enable security headers (HSTS, CSP, etc) when serving Unleash from HTTPS. Can also be configured through the environment variable SECURE_HEADERS.
  • versionCheck - the object deciding where to check for latest version
    • url - The url to check version (Defaults to - Overridable with (UNLEASH_VERSION_URL)
    • enable - Whether version checking is enabled (defaults to true) - Overridable with (CHECK_VERSION) (if anything other than true, does not check)
  • email - the email object configuring an SMTP server for sending welcome mails and password reset mails
    • host - The server URL to your SMTP server
    • port - Which port the SMTP server is running on. Defaults to 465 (Secure SMTP)
    • secure (boolean) - Whether to use SMTPS or not.
    • sender - Which email should be set as sender of mails being sent from Unleash?
    • smtpuser - Username for your SMTP server
    • smtppass - Password for your SMTP server

Disabling Auto-Start#

If you're using Unleash as part of a larger express app, you can disable the automatic server start by calling server.create. It takes the same options as server.start, but will not begin listening for connections.

const unleash = require('express');
const unleash = require('unleash-server');
const app = express();
const start = async () => {
const instance = await unleash.create({
databaseUrl: 'postgres://unleash_user:password@localhost:5432/unleash',
console.log(`Unleash app generated and attached to parent application`);

Graceful shutdown#

PS! Unleash will listen for the SIGINT signal and automatically trigger graceful shutdown of Unleash.

If you need to stop Unleash (close database connections, and stop running Unleash tasks) you may use the stop function. Be aware that it is not possible to restart the Unleash instance after stopping it, but you can create a new instance of Unleash.

const express = require('express');
const unleash = require('unleash-server');
const app = express();
const start = async () => {
const instance = await unleash.start({
databaseUrl: 'postgres://unleash_user:password@localhost:5432/unleash',
port: 4242,
//Sometime later
await instance.stop();
console.log('Unleash has now stopped');

Securing Unleash#

You can integrate Unleash with your authentication provider (OAuth 2.0). Read more about securing unleash.

How do I configure the log output?#

By default, unleash uses log4js to log important information. It is possible to swap out the logger provider (only when using Unleash programmatically). You do this by providing an implementation of the getLogger function as This enables filtering of log levels and easy redirection of output streams.

function getLogger(name) {
// do something with the name
return {
debug: console.log,
info: console.log,
warn: console.log,
error: console.error,

The logger interface with its debug, info, warn and error methods expects format string support as seen in debug or the JavaScript console object. Many commonly used logging implementations cover this API, e.g., bunyan, pino or winston.

Database pooling connection timeouts#

  • Please be aware of the default values of connection pool about idle session handling.
  • If you have a network component which closes idle sessions on tcp layer, please ensure, that the connection pool idleTimeoutMillis setting is lower than the timespan as the network component will close the idle connection.