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Lua (server-side) SDK 1.x to 2.0 migration guide

Read time: 11 minutes
Last edited: Dec 28, 2023

Overview

This topic explains the changes in the Lua SDK 2.0 release and how to adapt code that uses a 1.x version of the Lua SDK to use version 2.0 or later.

Version 2.0 includes several breaking changes. Additionally, if you use the Relay Proxy, you must update your Relay Proxy to version 7.0 before you update your SDK to version 2.0. To learn more, read the Relay Proxy 7.0 release notes. To upgrade to the latest Relay Proxy version, visit Relay Proxy releases on GitHub.

Understanding contexts

Many LaunchDarkly customers create targeting rules for feature flags based on a variety of different information, including attributes pertaining to users, organizations, devices, and more. In previous versions of the LaunchDarkly SDK, you could define this information in a user object, using a combination of built-in and custom attributes. Now you can define this information in a more structured way, using contexts.

Each context has a required attribute called kind that you can use to categorize context instances for targeting and Experimentation. You can also add other attributes. Attributes can be strings, booleans, numbers, arrays, or JSON objects.

When you evaluate a feature flag within your application, the flag's targeting rules use information from one or more kinds of contexts. For example, you may know:

  • the username, first name, last name, and email address of a person, as part of a context with kind of "user"
  • the company, department, and location of an organization, as part of a context with kind of "organization"
  • the device, model, and operating system of an environment, as part of a context with kind of "device"

This new version of the LaunchDarkly SDK requires you to evaluate feature flags using an evaluation context, which is an object containing one or more contexts.

To learn more about contexts, read Contexts and segments.

Migrating from users to contexts

The 2.0 version of this SDK lets you use contexts. When you migrate from version 1.x, replace every instance of a user with a context. If there are any instances you do not replace, the 2.0 version of the Lua SDK will convert the result of each makeUser call into a context with a context kind of "user."

LaunchDarkly assumes older versions of the SDK use user contexts

A context always has a kind attribute. When older versions of the Lua SDK send events to LaunchDarkly, LaunchDarkly will convert the users in those events to contexts with a kind of user.

If a flag configuration specifies any context kinds other than user, older versions of the Lua SDK will not evaluate the flag correctly. You must upgrade your SDK if you are going to use context kinds other than user in your flag configurations.

The primary differences between working with users and working with contexts include the following:

  • Changes to flag evaluation: The methods for evaluating flags now require contexts, rather than users.
  • Create contexts, not users: Where you previously created users, now you can create contexts.
  • Changes to attributes: There are now fewer built-in attributes. You can still add as many custom attributes as you like, although the format has changed slightly. A flag's targeting rules can now address fields within a JSON object.
  • Changes to private attributes: You can mark specific attributes of a context as private, either across all contexts of any kind, or within a particular context or context kind.
  • Changes to alias events: The alias method has been removed.

Understanding changes to flag evaluation

The methods for evaluating flags and determining flag evaluation reasons have changed slightly. The 2.0 version of the SDK includes the following changes:

  • The *Variation and *VariationDetail methods now take a context, rather than a user, as a parameter. To learn more, read Evaluating flags and Flag evaluation reasons.
  • The USER_NOT_SPECIFIED evaluation error code was previously defined as, the user object or user key was not provided. It has been redefined to mean that the context was not provided or was invalid.

Here's how to evaluate a flag using a context:

local value = client:boolVariation(context, 'flag-key-123abc', false);

Understanding differences between users and contexts

Where you previously created users, now you can create contexts.

In version 2, there are two ways to create contexts: makeContext and makeUser. makeUser is a convenience to make upgrading from the Lua SDK version 1.x to version 2.0 easier. It is deprecated and may be removed in future versions.

Here's how to construct a basic context, as compared with constructing a user:

local user = ld.makeUser({
key = "user-key-123abc"
})

The kind attribute is required when you use makeContext. You can omit the kind attribute when you use makeUser, and LaunchDarkly will assume the context kind is "user" when evaluating flags.

Overall, this should make your upgrade easier, because your existing code will continue to work, as long as you don't make changes to your flag configuration or bucket users based on the "secondary" attribute.

Here's how to construct a basic context, with a context kind of something other than "user":

local organization = ld.makeContext({
organization = {
key = "org-key-123abc"
}
})

Here's how to construct a multi-context, which includes multiple context kinds:

local context = ld.makeContext({
user = {
key = "user-key-123abc"
},
org = {
key = "org-key-123abc"
}
})

Understanding changes to built-in and custom attributes

This section describes the changes to built-in and custom attributes in the 2.0 version of the SDK.

Working with built-in and custom attributes



In the previous SDK version, the user object included several built-in attributes for describing the user. It also included optional custom attributes, which you could add to a custom object within the user object and then populate.

In version 2.0, the only built-in attributes are kind, key, name, and anonymous. kind, key, and name are strings, and anonymous is a boolean.

You can define additional attributes for a context by passing in a name and value for each. Additional attributes can be any JSON type, including boolean, number, string, array, or object. In version 2.0, you do not need to add custom attributes within a custom object.

Here's how to construct a context with additional attributes, as compared with constructing a similar user:

local user = ld.makeUser({
key = "user-key-123abc",
custom = {
address = { "123 Main St" }
}
})

Referencing properties of an attribute object



In previous versions of the SDK, if you set the value of a user's custom attribute to an object, you could not reference that object in evaluations. In version 2.0, if a context attribute's value is a JSON object, you can reference properties of that object as the attribute in the targeting rules for a flag or segment.

Here's how to add object attributes to a context:

local context = ld.makeContext({
user = {
key = "user2-key-123abc",
attributes = {
address = {
street = "123 Main St",
city = "Springfield"
}
}
}
})

In your flag or segment targeting, use / as the delimiter to refer to specific object fields. For example, you can use /address/city in your targeting. To learn more, read Targeting with flags.

Removing the secondary attribute



In previous versions of the SDK, you could set the value of a user's secondary attribute, as an optional secondary key for a user. The SDK would incorporate this attribute into the variation bucket assignment hash.

In version 2.0, the secondary attribute has been removed. If you were previously using this attribute as part of distinguishing percentage rollouts, that will no longer work for your customers.

Understanding changes to private attributes

As in previous versions of the SDK, you can mark specific attributes of a context as private. This restricts the context data your application sends to LaunchDarkly, while still using that data for flag targeting.

In version 2.0, there are two scopes for which you can mark attributes as private:

  • Across all contexts of any context kind. You might use this if you want to ensure that the SDK never stores an "email" attribute in LaunchDarkly, no matter whether it occurs in a user context, an organization context, or something else.
  • Within a particular context or context kind. You might use this if you want an "email" attribute to be private in a user context, but not in an organization context.

In the first example, all attributes are marked private for all contexts. Only the context key and kind are sent to LaunchDarkly. In the second example, the "email" and "address" attributes are private for all contexts:

local configAllPrivate = {
events = {
allAttributesPrivate = true
}
}

To learn more, read Private attributes.

Here's how to mark an attribute as private for a particular context:

local user = ld.makeContext({
user = {
key = "user-key-123abc",
attributes = {
firstName = "Sandy",
lastName = "Smith",
email = "sandy@example.com",
},
privateAttributes = { "email" }
}
})

For attributes that are objects, you can mark specific fields private, using the / delimiter followed by the attribute name, then the / delimiter followed by the JSON property within the value.

For example, for the attribute "address": { "street": "Main St", "city": "Springfield" }, you could set just the /address/street as private.

Understanding changes to alias events

In previous versions of the SDK, multiple user objects could represent one person. For example, this could happen the first time a person logged in to your application. The person might be represented by an anonymous user before they logged in, and a different user after they logged in. You could associate these two LaunchDarkly users by sending an alias event in the SDK.

With the introduction of contexts, the person in this scenario is represented by two different context kinds. For example, before they log in, they might be represented by a device context. After they log in, they might be represented by a multi-context, for example, by one context kind based on their device and simultaneously by another context kind based on their user information.

The 2.0 version of the SDK removes the ability to send an alias event. If you currently alias users, you will need to remove this code when you migrate to version 2.0.

If you want to continue associating two contexts with each other, you can use two different context kinds, and then identify a multi-context that includes both individual contexts when you want the association to occur. Unlike the aliasing method, the association doesn't persist between calls. You must send the contexts you want to associate in each variation or identify call and each track call.

Here's how:

-- create tables with the context attribute information
local device = {
key = "device-key-123abc"
}
local user = {
key = "user-key-123abc",
attributes = {
name = "Sandy"
}
}
-- use them to create contexts at different points in your application
local deviceContext = ld.makeContext({
device = device
})
client:identify(deviceContext)
local multiContext = ld.makeContext({
device = device,
user = user
})
client:identify(multiContext)

To learn more, read makeContext.

Understanding changes to configuration options

In the 2.0 version of the SDK, several configuration options have changed:

  • The privateAttributes and allAttributesPrivate configuration options both now apply to all contexts of any context kind. They are part of the broader events option. To learn more, read Understanding changes to private attributes.
  • The inlineUsersInEvents option has been removed.
  • The userKeysCapacity and userKeysFlushInterval options are removed. The userKeysCapacity option is replaced with contextKeysCapacity. There is no replacement for userKeysFlushInterval as the algorithm now evicts keys only when necessary.
  • The configuration options for the streaming, polling, and events URLs have changed: streamURI, baseURI, and eventsURI are replaced with the serviceEndpoints endpoints property, which has options for streamingBaseURL, pollingBaseURL, and eventsBaseURL. It is rare to set these configuration options. To learn more, read Service endpoint configuration.
  • The configuration options for setting up logging have changed. The registerLogger has been removed. Instead, use the logging configuration to set options for the default logger, or replace the default logger with a custom one. To learn more, read Logging.

To learn more about configuration options, read clientInit.

Understanding changes to storing data

If you use a persistent feature store without connecting to LaunchDarkly, you must update how you configure the SDK for this situation. In the 2.0 version of the SDK, this configuration is now set through the lazyLoad config option. The functionality has changed: the SDK reads flag data from the persistent store lazily, in the background, but it does not write to it. The data must be updated by an external process such as Relay Proxy.

Here's how:

local config = {
dataSystem = {
lazyLoad = {
source = makeYourSource()
}
}
}

If you currently use a persistent feature store and also have the SDK connect to LaunchDarkly, you can no longer do so in version 2.0. This is an uncommon configuration.

You could consider either using the Relay Proxy to populate a persistent feature store, or populating the store with another SDK that is capable of this. Then, configure the Lua SDK to use lazy loading.

To learn more, read Storing data.