Go

Eppo's open source Go SDK can be used for both feature flagging and experiment assignment:

• GitHub repository
• Package

1. Install the SDK

In your go.mod, add the SDK package as a dependency:

require (
    github.com/Eppo-exp/golang-sdk/v5
)

Or you can install the SDK from the command line with:

go get github.com/Eppo-exp/golang-sdk/v5

2. Initialize the SDK

Initialize the SDK with a SDK key, which can be generated in the Eppo interface. Initialization should happen when your application starts up to generate a singleton client instance, once per application lifecycle:

import (
  "github.com/Eppo-exp/golang-sdk/v5/eppoclient"
)

var eppoClient = &eppoclient.EppoClient{}

func main() {
  eppoClient, err = eppoclient.InitClient(eppoclient.Config{
    SdkKey: "<your_sdk_key>",
  })
}

After initialization, the SDK begins polling Eppo's API at regular intervals to retrieve the most recent experiment configurations such as variation values and traffic allocation. The SDK stores these configurations in memory so that assignments thereafter are effectively instant. For more information, see the architecture overview page.

Define an assignment logger (experiment assignment only)

If you are using the Eppo SDK for experiment assignment (i.e randomization), pass in a callback logging function to the InitClient function on SDK initialization. The SDK invokes the callback to capture assignment data whenever a variation is assigned.

The code below illustrates an example implementation of a logging callback using Segment. You could also use your own logging system, the only requirement is that the SDK receives a LogAssignment function.

Here we define an implementation of the Eppo IAssignmentLogger interface:

type IAssignmentLogger interface {
  LogAssignment(event eppoclient.AssignmentEvent)
}

Example implementation:

import (
  "github.com/Eppo-exp/golang-sdk/v5/eppoclient"
  "gopkg.in/segmentio/analytics-go.v3"
)

var eppoClient = &eppoclient.EppoClient{}

type ExampleAssignmentLogger struct {
  client analytics.Client
}

func (eal *ExampleAssignmentLogger) LogAssignment(event eppoclient.AssignmentEvent) {
  eal.client.Enqueue(analytics.Track{
    UserId:     event.Subject,
    Event:      "Eppo Randomization Event",
    Properties: analytics.Properties(event),
  })
}

func main() {
  // Connect to Segment (or your own event-tracking system)
  client := analytics.New("YOUR_WRITE_KEY")
  defer client.Close()

  eppoClient = eppoclient.InitClient(eppoclient.Config{
    SdkKey:           "<your_sdk_key>",
    AssignmentLogger: &ExampleAssignmentLogger{
      client: client,
    },
  })
}

The SDK will invoke the LogAssignment function with an event object that contains the following fields:

Field	Type	Description	Example
experiment	string	An Eppo experiment key	"recommendation-algo-allocation-17"
subject	string	An identifier of the subject or user assigned to the experiment variation	UUID
variation	string	The experiment variation the subject was assigned to	"control"
timestamp	string	The time when the subject was assigned to the variation	2021-06-22T17:35:12.000Z
subjectAttributes	map	A free-form map of metadata about the subject. These attributes are only logged if passed to the SDK assignment function	{ "country": "US" }
featureFlag	string	An Eppo feature flag key	"recommendation-algo"
allocation	string	An Eppo allocation key	"allocation-17"
metaData	map	Metadata around the assignment, such as the version of the SDK	{ "obfuscated": "true", "sdkLanguage": "javascript", "sdkLibVersion": "3.2.1" }
extraLogging	map	Metadata about the allocation.	{ "owner": "sam@company.ai" }

note

More details about logging and examples (with Segment, Rudderstack, mParticle, and Snowplow) can be found in the event logging page.

3. Assign variations

Assigning users to flags or experiments with a single GetStringAssignment function:

import (
    "github.com/Eppo-exp/golang-sdk/v5/eppoclient"
)

var eppoClient = &eppoclient.EppoClient{} // in global scope
variation, err := eppoClient.GetStringAssignment("<FLAG-KEY>", "<SUBJECT-KEY>", <TARGETING-ATTRIBUTES>, <DEFAULT-VALUE>);

The GetStringAssignment function takes 4 required inputs to assign a variation:

• FLAG-KEY - This key is available on the detail page for flags.
• SUBJECT-KEY - The ID of the entity that is being experimented on, typically represented by a uuid.
• TARGETING-ATTRIBUTES - An optional map of metadata about the subject used for targeting. If you create rules based on attributes on a flag, those attributes should be passed in on every assignment call.
• DEFAULT-VALUE - The default value to return if the SDK does not receive an assignment.

Typed assignments

Additional functions are available:

GetBooleanAssignment(...) (bool, error)
GetNumericAssignment(...) (float64, error)
GetIntegerAssignment(...) (int, error)
GetStringAssignment(...) (string, error)
GetJSONAssignment(...) (interface{}, error)

note

It may take up to 10 seconds for changes to Eppo experiments to be reflected by the SDK assignments.