Offline mode
Read time: 9 minutes
Last edited: Oct 18, 2023
Overview
This topic explains how to set an SDK to offline mode. Offline mode closes an SDK's connection to LaunchDarkly and switches to a feature flag's last known values.
A context is a generalized way of referring to the people, services, machines, or other resources that encounter feature flags in your product. Contexts replace another data object in LaunchDarkly: "users." To learn more, read Contexts.
Creating contexts and evaluating flags based on them is supported in the latest major versions of most of our SDKs. For these SDKs, the code samples on this page include the two most recent versions.
Using fallback values with client-side SDKs
For client-side SDKs, if an end user's device is not connected to a network, such as when the device is in airplane mode, the SDK uses the latest stored flag variation values in memory. If there are no previously stored variation values, the SDK uses the fallback values. The fallback values are defined in your code. The SDK returns the fallback value if it encounters an error or if LaunchDarkly is unreachable.
In some situations, you might want avoid remote calls to LaunchDarkly and use fallback values for your feature flags. For example, if your software is both cloud-hosted and distributed to customers to run on-premises, it might make sense to use fallback values when running on-premises. You can do this by setting offline mode in the client's config object. When the client is in offline mode, it makes no network requests, so it is suitable for unit-testing.
Details about each SDK's configuration are available in the SDK-specific sections below.
Client-side SDKs
This feature is available in the following client-side SDKs:
.NET (client-side)
Expand .NET (client-side) code sample
In some situations, you might want to stop making remote calls to LaunchDarkly and rely on locally cached flag values for future evaluations.
Here's how:
var config = Configuration.Builder("mobile-key-123abc", ConfigurationBuilder.AutoEnvAttributes.Enabled).Offline(true).Build();LdClient client = LdClient.Init(config);
Android
Expand Android code sample
In some situations, you might want to stop making remote calls to LaunchDarkly and rely on locally cached flag values for future evaluations.
Here's how:
LDConfig ldConfig = new LDConfig.Builder(AutoEnvAttributes.Enabled).mobileKey("mobile-key-123abc").setOffline(true).build();LDClient client = LDClient.init(this.getApplication(), ldConfig, context);// Or to switch an already-instantiated client to offline mode:client.setOffline();
Flutter
Expand Flutter code sample
In some situations, you might want to stop making remote calls to LaunchDarkly and rely on locally cached flag values for future evaluations.
Here's how:
LDConfig ldConfig = LDConfigBuilder('mobile-key-123abc', AutoEnvAttributes.Enabled).offline(true).build();await LDClient.start(ldConfig, context);// Or to switch an already-instantiated client to offline mode:await LDClient.setOnline(false);
iOS
Expand iOS code sample
In some situations, you might want to stop making remote calls to LaunchDarkly and rely on locally cached flag values for future evaluations.
The SDK protects itself from multiple rapid calls to setOnline(true)
by enforcing an increasing delay (called throttling) each time setOnline(true)
is called within a short time. The first time, the call proceeds normally. For each subsequent call, the delay is enforced, and if waiting, increased to a maximum delay. When the delay has elapsed, the setOnline(true)
proceeds, assuming that the client app has not called setOnline(false)
during the delay. Therefore, a call to setOnline(true)
may not immediately result in the LDClient going online.
Client app developers should consider this situation abnormal, and take steps to prevent the client app from making multiple rapid setOnline(true)
calls. Calls to setOnline(false)
are not throttled. Calls to start(config: context: completion:)
, and setting the config
or context
can also call setOnline(true)
under certain conditions. After the delay, the SDK resets and the client app can make a subsequent call to setOnline(true)
without being throttled.
Client apps can set a completion closure called when the setOnline call completes. For unthrottled setOnline(true)
and all setOnline(false)
calls, the SDK calls the closure immediately on completion of this method. For throttled setOnline(true)
calls, the SDK calls the closure after the throttling delay at the completion of the setOnline
method.
The SDK does not go online if the client has not been started, or the mobileKey
is empty. For macOS, the SDK does not go online in the background unless enableBackgroundUpdates
is true.
Use isOnline
to get the online/offline state.
Here is an example:
LDClient.get()!.setOnline(false)LDClient.get()!.setOnline(true) {// Client is online}let connectionStatus = LDClient.get()!.isOnline
React Native
Expand React Native code sample
In some situations, you might want to stop making remote calls to LaunchDarkly and rely on locally cached flag values for future evaluations.
Here's how:
let offlineResult = client.setOffline(); //true or falselet offlineStatus = client.isOffline(); //true or falselet onlineResult = client.setOnline(); //true or false
Server-side SDKs
This feature is available in the following server-side SDKs:
- .NET (server-side)
- C/C++ (server-side)
- Erlang
- Go
- Haskell
- Java
- Node.js (server-side)
- PHP
- Python
- Ruby
- Rust
.NET (server-side)
Expand .NET (server-side) code sample
In some situations, you might want to stop making remote calls to LaunchDarkly and rely on locally cached flag values for future evaluations.
Here's how:
var config = Configuration.Builder("sdk-key-123abc").Offline(true).Build();LdClient client = new LdClient(config);
C/C++ (server-side)
Expand C/C++ (server-side) code sample
In some situations, you might want to stop making remote calls to LaunchDarkly and rely on locally cached flag values for future evaluations.
Here's how:
LDConfigSetOffline(config, true);
Erlang
Expand Erlang code sample
In some situations, you might want to stop making remote calls to LaunchDarkly and rely on locally cached flag values for future evaluations.
Here's how:
ldclient:start_instance("sdk-key-123abc", #{offline => true})
Go
Expand Go code sample
In some situations, you might want to stop making remote calls to LaunchDarkly and rely on locally cached flag values for future evaluations.
Here's how:
var config ld.Configconfig.Offline = trueclient, _ := ld.MakeCustomClient("sdk-key-123abc", config, 5*time.Second)client.BoolVariation("any.feature.flag", context, false) // will always return the default value (false)
Haskell
Expand Haskell code sample
In some situations, you might want to stop making remote calls to LaunchDarkly and rely on locally cached flag values for future evaluations.
Here's how:
config' = configSetOffline True config
Java
Expand Java code sample
In some situations, you might want to stop making remote calls to LaunchDarkly and rely on locally cached flag values for future evaluations.
Here's how:
LDConfig config = new LDConfig.Builder().offline(true).build();LDClient client = new LDClient("sdk-key-123abc", config);client.boolVariation("flag-key-123abc", context, false)// This call to client.boolVariation always// returns the default value (false)
Node.js (server-side)
Expand Node.js (server-side) code sample
In some situations, you might want to stop making remote calls to LaunchDarkly and rely on locally cached flag values for future evaluations.
Here's how:
import * as ld from '@launchdarkly/node-server-sdk';const options: ld.LDOptions = { offline: true };const client = ld.init('sdk-key-123abc', options);client.variation('any.feature.flag', context, false, cb); // cb will always be invoked with the default value (false)
The default value you set in the variation method is returned in offline mode. This does not refer to the default rule set in your flag configuration.
PHP
Expand PHP code sample
In some situations, you might want to stop making remote calls to LaunchDarkly and rely on locally cached flag values for future evaluations.
Here's how:
$client = new LaunchDarkly\LDClient("sdk-key-123abc", ["offline" => true]);$client->variation("any.feature.flag", $context, false); // will always return the default value (false)
Python
Expand Python code sample
In some situations, you might want to stop making remote calls to LaunchDarkly and rely on locally cached flag values for future evaluations.
Here's how:
# Initialization:ldclient.set_config(Config("sdk-key-123abc", offline=True))ldclient.get().variation("any.feature.flag", context, False) # will always return the default value (false)
Ruby
Expand Ruby code sample
In some situations, you might want to stop making remote calls to LaunchDarkly and rely on locally cached flag values for future evaluations.
Here's how:
config = LaunchDarkly::Config.new({offline: true})client = LaunchDarkly::LDClient.new("sdk-key-123abc", config)client.variation("any.feature.flag", context, false) # will always return the default value (false)
Rust
Expand Rust code sample
In some situations, you might want to stop making remote calls to LaunchDarkly and rely on locally cached flag values for future evaluations.
Here's how:
let config = ConfigBuilder::new("sdk-key-123abc").offline(true).build();let ld_client = Client::build(config).unwrap();ld_client.bool_variation(&context, "flag-key-123abc", false); // will always return the default value (false)