Logging configuration

The client-side .NET SDK uses the Common.Logging framework. For an example configuration, read the Common.Logging README.

There are two important things to consider before you enable the DEBUG log level:

1. Debug-level logs can be very verbose. We do not recommend using debug logging in high-volume environments.
2. Debug-level logs include sensitive information, including LaunchDarkly contexts you create when you use this SDK.

The Android SDK makes heavy use of Timber logging. Include Timber in your application to enable debug output or production logging. An example is shown below to enable debug output when the application is built with a debug configuration.

Here's how:

if (BuildConfig.DEBUG) {
    Timber.plant(new Timber.DebugTree());
}
COPY

By default, there is no log output, but we provide a default logger you can enable. The SDK does not lock on any logging. Ensure that your implementation is thread safe.

Whether you use a custom logger or the default one, you must use the LoggingBuilder to configure logging before the client is initialized. You cannot modify logging while the client is running.

If you use the default logger, you can configure how verbose it should be. The options are debug, info, warn, and error.

Here is an example:

auto config_builder = client_side::ConfigBuilder("mobile-key-123abc");
config_builder.Logging()
  .Logging(LoggingBuilder::BasicLogging().Tag("ArbitraryLogTag").Level(LogLevel::kWarn));
auto config = config_builder.Build();
COPY

You can also use your own custom log function.

First, implement the log backend interface. For C++, this means implementing the ILogBackend interface. If you are working with the C binding, define the callback functions to implement the log backend interface.

Here's how:

#include <launchdarkly/logging/log_level.hpp>
#include <launchdarkly/logging/log_backend.hpp>
using namespace launchdarkly;
class CustomLogger : public ILogBackend {
   public:
    /* Should return true if the specified level is enabled; in this example, return true to log all messages. */
    bool Enabled(LogLevel level) noexcept override { return true; }
    /* Forwards to stdout as an example, printing the log tag along with the message. */
    void Write(LogLevel level, std::string message) noexcept override {
        std::cout << GetLogLevelName(level, "unknown") << ": " << message << std::endl;
}
};
COPY

Then, install the custom logger in the SDK's config:

// Make sure the <memory> header is included for std::make_shared
#include <memory>
auto config_builder = client_side::ConfigBuilder("mobile-key-123abc");
config_builder.Logging()
  .Logging(LoggingBuilder::CustomLogging().Backend(std::make_shared<CustomLogger>()));
auto config = config_builder.Build();
COPY

By default, the SDK uses the winston package. There are four logging levels: debug, info, warn, and error. By default, debug messages are hidden.

To change the logging configuration, you can set LDOptions.logger to either another Winston instance or any object that implements the LDLogger interface. The createConsoleLogger function creates a minimal logger.

The Flutter SDK supports logging in version 4 and later.

There are four logging levels in the Flutter SDK: debug, info, warn, and error. You can also set the level to none to disable all logging.

By default, the SDK logs at the info level with a tag of "LaunchDarkly." To change the logging, construct an LDLogger and include it in your LDConfig. You can change the log level, tag, and output destinations when you construct the logger.

Here's how:

final logger = LDLogger(level: LDLogLevel.warn);
final config = LDConfig(
  CredentialSource.fromEnvironment,
  AutoEnvAttributes.enabled,
  logger: logger,
);
COPY

Optionally, you can create a custom logging implementation. Your implementation should use the LDLogAdapter interface.

To learn more, read LDLogger.

The iOS SDK emits log messages using calls to os_log. The SDK provides a default logger OSLog(subsystem: "com.launchdarkly", category: "ios-client-sdk"). This logger can be overridden using the LDConfig.logger property.

Here's how:

import OSLog
var config = LDConfig(mobileKey: 'mobile-key-123abc', autoEnvAttributes: .enabled)
config.logger = OSLog(subsystem: "your.preferred.subsystem", category: "ld-sdk")
// You can disable all SDK logging by setting this property to the shared disabled logger
config.logger = .disabled
COPY

In the default configuration, the SDK sends the output to the console and enables all log levels except debug.

To change the logging configuration, set LDOptions.logger to any object that implements the LDLogger interface and performs logging for the client. To learn more, read LDOptions and LDLogger in the SDK API docs.

The client-side Node.js SDK offers several choices for logging.

In the default configuration, the SDK sends output to the console and enables all log levels except debug.

Versions 1.x of the SDK used the winston logging package for the default configuration. Versions 2.0 and later do not have a dependency on winston. Instead, they write directly to the console by default.

For full control over logging behavior, you can set the logger option to an object that implements the LDLogger interface. To learn more about the logger's requirements and methods, read LDLogger. The winston package is compatible with this interface, so if you are already using a winston logger, you can pass it directly to the SDK.

You can use basicLogger for simpler control over logging behavior. Versions 2.x and earlier of the SDK do not support basicLogger.

This example shows how to use basicLogger to enable debug-level logging in your SDK configuration:

const LaunchDarkly = require('launchdarkly-node-client-sdk');
const options = {
  logger: LaunchDarkly.basicLogger({
    level: 'debug',
  }),
};
const client = LaunchDarkly.initialize( 'client-side-id-123abc', user, options);
COPY

Be aware of two considerations when enabling debug-level logging:

1. Debug-level logs can be very verbose. We do not recommend using debug logging in high-volume environments.
2. Debug-level logs include sensitive information, including LaunchDarkly users you create when you use this SDK.

By default, the React Native SDK uses BasicLogger. This sends output to the console, with a default log level of info.

You can use BasicLogger to make some changes to logging behavior. For full control over logging behavior, you can set the LDOptions.logger option to an object that implements the LDLogger interface and performs logging for the client.

This example shows how to use BasicLogger to enable debug-level logging in your SDK configuration:

import {
  AutoEnvAttributes,
  BasicLogger,
  type LDOptions,
  ReactNativeLDClient,
} from '@launchdarkly/react-native-client-sdk';
const options: LDOptions = {
  logger: new BasicLogger({
    level: 'debug',
    destination: console.log,
  }),
};
const featureClient = new ReactNativeLDClient('mobile-key-123abc', AutoEnvAttributes.Enabled, options);
COPY

To learn more, read LDOptions and LDLogger.

The React Web SDK relies on the JavaScript SDK for logging-related functionality. In the default configuration, the SDK sends the output to the console and enables all log levels except debug.

To change the logging configuration, set LDOptions.logger to any object that implements the LDLogger interface and performs logging for the client. The basicLogger, available in the JavaScript SDK, produces such an object.

Here's how:

import { basicLogger } from 'launchdarkly-js-client-sdk';
export default withLDProvider({
  clientSideID: 'client-side-id-123abc',
  options: {
    logger: basicLogger({level: 'debug'})
  }
})(App);
COPY

To learn more, read LDOptions and LDLogger in the JavaScript SDK API docs.

The Roku SDK's logging feature is configurable. You can set different log levels, or use a custom logging backend with one of the two supported custom loggers.

Those loggers are:

• Legacy API custom logger for the Roku SDK
• SceneGraph API custom logger for the Roku SDK

Log levels in the Roku SDK

You can configure the SDK log level. For example, to set the level to info:

config.setLogLevel(LaunchDarklyLogLevels().info)
COPY

The SDK supports the following Levels:

LaunchDarklyLogLevels().error
LaunchDarklyLogLevels().warn
LaunchDarklyLogLevels().info
LaunchDarklyLogLevels().debug
LaunchDarklyLogLevels().none
COPY

Legacy API custom logger for the Roku SDK

Here is an example of the legacy API custom logger:

function CustomLogger() as Object
    return {
        log: function(level as Integer, message as String)
            print level message
        end function
    }
end function
config.setLogger(CustomLogger())
COPY

SceneGraph API custom logger for the Roku SDK

Here is an example of the SceneGraph API custom logger:

<!-- /components/CustomLogger.xml -->
<component name="CustomLogger" extends="Task">
    <interface>
        <field id="log" type="assocarray" alwaysNotify="true"/>
    </interface>
    <script type="text/brightscript" uri="pkg:/components/CustomLogger.brs"/>
</component>
COPY

To use the logger, create the SceneGraph logger node, and then:

config.setLoggerNode(myLoggerNode)
COPY

The .NET SDK has four logging levels: Debug, Info, Warn, and Error. By default, the lowest enabled level is Info, so Debug messages are hidden. There are two important things to consider if you enable the Debug level:

1. Debug-level logs can be very verbose. We do not recommend using debug logging in high-volume environments.
2. Debug-level logs include sensitive information, including LaunchDarkly contexts you create when you use this SDK.

The .NET SDK sends log output to Console.Error by default. The ConfigurationBuilder.Logging method and the LaunchDarkly.Logging API allow you to change the output destination and log level.

Here is an example:

using LaunchDarkly.Logging;
using LaunchDarkly.Sdk.Server;
var config = Configuration.Builder("sdk-key-123abc")
    .Logging(
        Components.Logging(Logs.ToWriter(Console.Out)).Level(LogLevel.Debug)
    )
    .Build();
COPY

The destination could be another logging framework, such as the .NET Core Microsoft.Extensions.Logging API in this example:

using LaunchDarkly.Logging;
using LaunchDarkly.Sdk.Server;
var config = Configuration.Builder("sdk-key-123abc")
    .Logging(Logs.CoreLogging)
    .Build();
COPY

To learn more about logging configuration and adapters for other logging frameworks, read the documentation for LaunchDarkly.Logging.

All log messages from the SDK are tagged with a logger name, indicating the category of messages. If you use a logging framework like Microsoft.Extensions.Logging or NLog, you can use these names to filter the output:

• LaunchDarkly.Sdk: general messages about the operation of the SDK client.
• LaunchDarkly.Sdk.DataSource: messages about how the SDK client receives feature flag data, such as if the connection to LaunchDarkly has been interrupted.
• LaunchDarkly.Sdk.DataStore (or more specific names like LaunchDarkly.Sdk.DataStore.Redis): messages about how the SDK client stores feature flag data, such as if you are using a database integration.
• LaunchDarkly.Sdk.Evaluation: messages about unusual conditions during feature flag evaluation, such as if a feature flag could not be evaluated because its configuration is invalid.
• LaunchDarkly.Sdk.Events: messages about analytics events, such as if event data could not be sent to LaunchDarkly due to a network problem.

Before version 6.0, the .NET SDK had different logging behavior:

• The mechanism for specifying a log destination was the Common.Logging framework.
• If you did not specifically configure a log destination using Common.Logging, logging was disabled by default.
• The main logger name was LaunchDarkly.Client.LdClient.

By default, there is no log output, but we provide a default logger you can enable. The SDK does not lock on any logging. Ensure that your implementation is thread safe.

Whether you use a custom logger or the default one, you must use the LoggingBuilder to configure logging before the client is initialized. You cannot modify logging while the client is running.

If you use the default logger, you can configure how verbose it should be. The options are debug, info, warn, and error.

Here is an example:

auto config_builder = server_side::ConfigBuilder("sdk-key-123abc");
using LoggingBuilder = server_side::config::builders::LoggingBuilder;
config_builder.Logging().Logging(
  LoggingBuilder::BasicLogging().Tag("ArbitraryLogTag").Level(LogLevel::kWarn)
);
COPY

You can also use your own custom log function.

First, implement the log backend interface. For C++, this means implementing the ILogBackend interface. If you are working with the C binding, define the callback functions to implement the log backend interface.

Here's how:

#include <launchdarkly/logging/log_level.hpp>
#include <launchdarkly/logging/log_backend.hpp>
using namespace launchdarkly;
class CustomLogger : public ILogBackend {
   public:
    /* Should return true if the specified level is enabled; in this example, return true to log all messages. */
    bool Enabled(LogLevel level) noexcept override { return true; }
    /* Forwards to stdout as an example, printing the log tag along with the message. */
    void Write(LogLevel level, std::string message) noexcept override {
        std::cout << GetLogLevelName(level, "unknown") << ": " << message << std::endl;
}
};
COPY

Then, install the custom logger in the SDK's config:

// Make sure the <memory> header is included for std::make_shared
#include <memory>
config_builder.Logging().Logging(LoggingBuilder::CustomLogging().Backend(
  std::make_shared<CustomLogger>()));
auto config = config_builder.Build();
COPY

The Go SDK uses a logging abstraction that can write to a log.Logger or anything with a compatible interface. This adds a system of log levels similar to logging frameworks on other platforms. There are four logging levels: Debug, Info, Warn, and Error.

By default, all levels of messages are enabled except Debug. You can tell the SDK to enable more or fewer levels, to send the output to a different destination, or to disable logging.

Here's how:

import (
    "log"
    "os"
    ldlog "github.com/launchdarkly/go-sdk-common/v3"
    ld "github.com/launchdarkly/go-server-sdk/v6"
    "github.com/launchdarkly/go-server-sdk/v6/ldcomponents"
)
var config ld.Config
loggers := ldlog.NewDefaultLoggers()
// Send output to a file
file, _ := os.Create("app.log")
loggers.SetBaseLogger(log.New(file, "", log.LstdFlags))
config.Logging = ldcomponents.Logging().
    Loggers(loggers).
    MinLevel(ldlog.Warn) // Change minimum level to Warn (Debug and Info are disabled)
// Or, disable logging
config.Logging = ldcomponents.NoLogging()
COPY

There are two things to consider if you enable the Debug log level:

1. Debug-level logs can be very verbose. We do not recommend using debug logging in high-volume environments.
2. Debug-level logs include sensitive information, including LaunchDarkly contexts you create when you use this SDK.

In version 5.10.0 and higher, the Java SDK allows you to specify a destination for logging using the LDConfig.Builder.logging method and the com.launchdarkly.logging API.

If you do not specify a destination, the default behavior depends on the version of the SDK:

• In versions 5.10.0 and earlier, the default destination is SLF4J. SLF4J has its own configuration mechanisms for determining where output will go, and for filtering by level and/or logger name. It will not generate any output unless you have provided a configuration. For an example of using SLF4J with a simple console logging configuration, visit an SLF4J-specific version of hello-java.
• Starting with version 6.0.0, the SDK does not require SLF4J. Instead, it detects whether the application is already using SLF4J. If the SLF4J classes are present in the classpath, then it sends log output to SLF4J by default. If the SLF4J classes are not present in the classpath, then it sends log output to System.err by default.

Here is an example of configuring log output to go to the standard output stream (System.out), and enabling DEBUG level:

import com.launchdarkly.logging.*;
import com.launchdarkly.sdk.server.*;
LDConfig config = new LDConfig.Builder()
  .logging(
    Components.logging(Logs.toStream(System.out)).level(LDLogLevel.DEBUG)
  )
  .build();
COPY

To learn more about logging configuration and adapters for other logging frameworks, read the documentation for com.launchdarkly.logging.

All log messages from the SDK are tagged with a logger name, indicating the category of messages. If you use a logging framework like SLF4J, you can use these names to filter the output:

• com.launchdarkly.sdk.server.LDClient: This is for general messages that do not fall into any other categories.
• com.launchdarkly.sdk.server.LDClient.DataSource: This is for messages related to how the SDK obtains feature flag data. Usually, this means messages about the streaming connection to LaunchDarkly, but if you use polling mode or file data instead, the SDK logs those messages under this name.
• com.launchdarkly.sdk.server.LDClient.DataStore: This is for messages related to how feature flag data is stored. For example, database errors appear here if you are using a database integration.
• com.launchdarkly.sdk.server.LDClient.Evaluation: This is for messages related to feature flag evaluation.
• com.launchdarkly.sdk.server.LDClient.Events: This is for messages related to analytics event processing.

In versions of the SDK before 5.0, logger names were not standardized and were sometimes the names of Java classes that are not part of the public API, but they consistently had a package prefix of either com.launchdarkly.client. or com.launchdarkly.eventsource.

There are two important things to consider before you enable the DEBUG log level:

1. Debug-level logs can be very verbose. We do not recommend using debug logging in high-volume environments.
2. Debug-level logs include sensitive information, including LaunchDarkly contexts you create when you use this SDK.

The SDK configures a default logger if not otherwise specified. You may modify the behavior of the default logger by specifying a custom log tag and minimum log level, or you may completely replace it with a custom logging implementation.

The SDK does not lock on any logging, so ensure that your custom implementation is thread safe.

You cannot modify logging while the client is running.

If you use the default logger, you can configure how verbose it should be. The options are 'debug', 'info', 'warn', and 'error'.

Here is an example:

local config = {
    logging = {
        basic = {
            tag = "launchdarkly",
            level = "warn"
        }
    }
}
COPY

You can also use a custom logger. Here's how:

local logger = ld.makeLogBackend(
    function(level)
        -- Log everything.
        return true
    end,
    function(level, message)
        -- Prints in the format: '[level] hello world'
        print(string.format("[%s] %s", level, message))
    end
)
local config = {
    logging = {
        custom = logger
    }
}
COPY

The Node.js SDK offers several choices for logging.

In the default configuration, the SDK sends output to the console and enables all log levels except debug.

Pre-6.0 versions of the SDK used the winston logging package for the default configuration. Versions 6.0 and later write directly to the console by default.

For full control over logging behavior, you can set the logger option to an object that implements the LDLogger interface. To learn more about the logger's requirements and methods, read LDLogger.

You can use basicLogger for simpler control over logging behavior. Versions 5.x and earlier of the SDK do not support basicLogger.

This example shows how to use basicLogger to enable debug-level logging in your SDK configuration:

import * as ld from '@launchdarkly/node-server-sdk';
const logger: ld.LDLogger = ld.basicLogger({
  level: 'debug',
  destination: console.log,
});
const options: ld.LDOptions = { logger: logger };
COPY

There are two important things to consider before you enable debug-level logging:

1. Debug-level logs can be very verbose. We do not recommend using debug logging in high-volume environments.
2. Debug-level logs include sensitive information, including LaunchDarkly users you create when you use this SDK.

The PHP SDK uses Monolog. All loggers are namespaced under LaunchDarkly.

There are two important things to consider before you enable the DEBUG log level:

1. Debug-level logs can be very verbose. We do not recommend using debug logging in high-volume environments.
2. Debug-level logs include sensitive information, including LaunchDarkly contexts you create when you use this SDK.

You can pass a custom logger to the SDK by using the configurable logger property:

$client = new LaunchDarkly\LDClient("sdk-key-123abc", ["logger" => new Logger("LaunchDarkly", [new ErrorLogHandler(0, Level::Debug)])]);
COPY

The Python SDK uses Python's built-in logging library.

Here's how to enable the debug log level:

ld_logger = logging.getLogger("ldclient")
ld_logger.setLevel(logging.DEBUG)
COPY

There are two important things to consider before you enable the debug log level:

• Debug-level logs can be very verbose. We do not recommend using debug logging in high-volume environments.
• Debug-level logs include sensitive information, including LaunchDarkly users you create when you use this SDK.

The Ruby SDK uses Ruby's built-in Logger class. All loggers are namespaced under [LDClient].

There are two important things to consider before you enable the DEBUG log level:

1. Debug-level logs can be very verbose. We do not recommend using debug logging in high-volume environments.

2. Debug-level logs include sensitive information, including LaunchDarkly contexts you create when you use this SDK.

   You can pass a custom logger to the SDK by using the configurable logger property:

   Ruby

   log = ::Logger.new($stdout)
   log.level = ::Logger::DEBUG
   config = LaunchDarkly::Config.new({logger: log})
   client = LaunchDarkly::LDClient.new("sdk-key-123abc", config)
   COPY

The Rust SDK uses the log crate.

There are two important things to consider before you enable the DEBUG log level:

1. Debug-level logs can be very verbose. We do not recommend using debug logging in high-volume environments.
2. Debug-level logs include sensitive information, including LaunchDarkly contexts you create when you use this SDK.

In the default configuration, the SDK sends output to the console and enables all log levels except debug.

For full control over logging behavior, you can set the logger option to an object that implements the LDLogger interface. To learn more about the logger's requirements and methods, read LDLogger.

This example shows how to use BasicLogger to enable debug-level logging in your SDK configuration:

import { BasicLogger, LDOptions } from '@launchdarkly/cloudflare-server-sdk';
const options: LDOptions = {
  logger: new BasicLogger({ level: 'debug', }),
};
COPY

In the default configuration, the SDK sends output to the console and enables all log levels except debug.

This example shows how to use BasicLogger to enable debug-level logging in your SDK configuration:

import { BasicLogger, LDOptions } from '@launchdarkly/vercel-server-sdk';
const options: LDOptions = {
  logger: new BasicLogger({ level: 'debug', }),
};
COPY

For full control over logging behavior, you can set the logger option to an object that implements the LDLogger interface. To learn more about the logger's requirements and methods, read LDLogger.