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Go SDK reference

note

This SDK works with Harness Self-Managed Enterprise Edition (on premises).

This topic describes how to use the Harness Feature Flags Go SDK for your Go application. 

For getting started quickly, you can use our sample code from the SDK README. You can also clone and run a sample application from the Go SDK GitHub Repository.

Before you begin​

Make sure you read and understand:

Version​

The current version of this SDK is 0.1.8.

Requirements​

To use this SDK, make sure you:

Install the SDK​

Install the SDK using the following Go command:

go get github.com/harness/ff-golang-server-sdk

Import the SDK​

Import the SDK using the following Go command: 

import harness "github.com/harness/ff-golang-server-sdk/client"

Initialize the SDK​

To initialize the Go SDK, you need to:

  1. Add your Server SDK Key to connect to your Harness Environment.
  2. (Optional) Configure the SDK options. For more details on what features you can configure for this SDK, go to Configure the SDK.
  3. Complete the initialization by creating an instance of the Feature Flag client and  passing in the Server SDK Key and Configuration.
  4. Add a Target that you want to Evaluate against a Feature Flag.

Add the Server SDK Key​

To connect to the correct Environment that you set up on the Harness Platform, you need to add the Server SDK Key from that Environment. Input the Server SDK Key into the sdkKey parameter. For example:

client, err := harness.NewCfClient(sdkKey)

Configure the SDK​

You can configure the following features of the SDK:

NameExampleDescriptionDefault Value
baseUrlharness.WithURL("https://config.ff.harness.io/api/1.0")The URL used to fetch Feature Flag Evaluations. When using the Relay Proxy, change this to: http://localhost:7000https://config.ff.harness.io/api/1.0
eventUrlharness.WithEventsURL("https://events.ff.harness.io/api/1.0")The URL for posting metrics data to the Feature Flag service. When using the Relay Proxy, change this to: http://localhost:7000https://events.ff.harness.io/api/1.0
pollIntervalharness.WithPullInterval(60))The interval in seconds that we poll for changes when you are using stream mode.60 (seconds)
streamEnabledharness.WithStreamEnabled(false)Set to true to enable streaming mode.Set to false to disable streaming mode.true
analyticsEnabledharness.WithAnalyticsEnabled(false)Set to true to enable analytics.Set to false to disable analytics.Note: Analytics are not cached.true

Enabling analytics is currently not available using the Go SDK.For further configuration options and samples, such as configuring your logger or using the SDK with the Relay Proxy, go to Additional Options.

Complete the initialization​

Complete  the initialization by creating an instance of the Feature Flag client and passing in the sdkKey, and any configuration options. For example:

// Create Options  
client, err := harness.NewCfClient(myApiKey,   
 harness.WithURL("https://config.ff.harness.io/api/1.0"),   
 harness.WithEventsURL("https://events.ff.harness.io/api/1.0"),   
 harness.WithPullInterval(1),  
 harness.WithStreamEnabled(false))

Add a Target​

What is a Target?
Targets are used to control which users see which Variation of a Feature Flag, for example, if you want to do internal testing, you can enable the Flag for some users and not others. When creating a Target, you give it a name and a unique identifier. Often Targets are users but you can create a Target from anything that can be uniquely identified, such as an app or a machine.

For more information about Targets, go to Targeting Users With Flags.

To add a Target, build it and pass in arguments for the following:

ParameterDescriptionRequired?Example
IdentifierUnique ID for the Target.Read Regex requirements for Target names and identifiers below for accepted characters.RequiredIdentifier: "HT_1"
NameName for this Target. This does not have to be unique. Note: If you don’t provide a value, the name will be the same as the identifier.Read Regex requirements for Target names and identifiers below for accepted characters.OptionalNote: If you don't want to send a name, don't send the parameter. Sending an empty argument will cause an error.Name: "Harness_Target_1"
AttributesAdditional data you can store for a Target, such as email addresses or location.OptionalAttributes: &map[string]interface{}{"email":"demo@harness.io"},
Regex requirements for Target names and identifiers

Identifier

Regex: ^[A-Za-z0-9.@_-]*$
Must consist of only alphabetical characters, numbers, and the following symbols:
. (period)
@ (at sign)
-(dash)
_ (underscore)

The characters can be lowercase or uppercase but cannot include accented letters, for example Cafe_789.

Name Regex: ^[\\p{L}\\d .@_-]*$

Must consist of only alphabetical characters, numbers, and the following symbols:
. (period)
@ (at sign)
-(dash)
_ (underscore)
(space)

The characters can be lowercase or uppercase and can include accented letters, for example Café_123.

For example:

Create a Target​

target2 := evaluation.Target{  
 Identifier: "HT_1",  
 Name: "Harness_Target_1",  
 Attributes: &map[string]interface{}{"email":"demo@harness.io"},  
}

Create a Target with the builder​

If you create a Target with the builder, use Custom instead of Attributes.

target := dto.NewTargetBuilder("HT_1").  
 Name("Harness_Target_1").  
 Custom("email", "demo@harness.io").  
 Build()

Evaluate a Flag​

Evaluating a Flag is when the SDK processes all Flag rules and returns the correct Variation of that Flag for the Target you provide. 

If a matching Flag can’t be found, or the SDK can’t remotely fetch flags, the default value is returned. 

There are different methods for the different Variation types and for each method you need to pass in:

  • Identifier of the Flag you want to evaluate
  • The Target object you want to evaluate against
  • The default Variation

For example:

Evaluate a string Variation​

client.StringVariation(flagName, &target, "default_string")

Evaluate a boolean Variation​

showFeature, err := client.BoolVariation(featureFlagKey, &target, false)

Evaluate a number Variation​

client.NumberVariation(flagName, &target, -1)

Evaluate a JSON Variation​

client.JSONVariation(flagName, &target, types.JSON{"darkmode": false})

Test Your App is Connected to Harness​

When you receive a response showing the current status of your Feature Flag, go to the Harness Platform and toggle the Flag on and off. Then, check your app to verify if the Flag Variation displayed is updated with the Variation you toggled.

note

The SDK must run for at least 60 seconds before it sends metrics. Please ensure metrics have not been disabled in the SDK.

Close the SDK client​

In most applications, you won't need to close the SDK client.

However, you should close the SDK client if:

  • Your application is about to terminate. Closing the client ensures that all associated resources are released.
  • You have determined that you do not need to evaluate flags again in your application lifecycle.
important

The SDK does not evaluate flags after the client is closed.

To close the SDK client:

  • Assuming you have initialized an SDK client instance named client, call the following function:

    client.close()

Additional options​

Configure your logger​

The SDK has a default logger, however, you can provide your own logger to the SDK by passing it in as a configuration option. 

For example, the following creates an instance of the logrus logger and passes it in as a configuration option:

logger := logrus.New()  
logger.SetLevel(logrus.ErrorLevel)  
  
 // Create a feature flag client  
client, err := harness.NewCfClient(sdkKey, harness.WithLogger(logger))

Use the Relay Proxy​

When using your Feature Flag SDKs with a Harness Relay Proxy you need to change the default URL and events URL to http://localhost:7000 when initializing the SDK. For example:

client, err := harness.NewCfClient(apiKey,  
harness.WithURL("http://localhost:7000"),  
harness.WithEventsURL("http://localhost:7000"))

Sample code for a Go application​

Here is a sample code for integrating with the Go SDK:

package main  
  
 import (  
         "context"  
         "fmt"  
         "log"  
         "time"  
   
         harness "github.com/harness/ff-golang-server-sdk/client"  
         "github.com/harness/ff-golang-server-sdk/dto"  
         "github.com/sirupsen/logrus"  
)  
  
 const sdkKey = "your SDK key"  
  
 const featureFlag = "harnessappdemodarkmode"  
  
 func main() {  
  
        logger := logrus.New()  
        logger.SetLevel(logrus.ErrorLevel)  
      
        client, err := harness.NewCfClient(myApiKey,   
                 harness.WithURL("https://config.ff.harness.io/api/1.0"),   
                 harness.WithEventsURL("https://events.ff.harness.io/api/1.0”),   
                 harness.WithPullInterval(1),  
                 harness.WithLogger(logger),  
                 harness.WithStreamEnabled(false)  
)  
  
        defer func() {  
               if err := client.Close(); err != nil {  
                     log.Printf("error while closing client err: %v", err)  
               }  
         }()  
  
        if err != nil {  
                 log.Printf("could not connect to CF servers %v", err)  
         }  
  
        target := dto.NewTargetBuilder("HT_1").  
                 Name("Harness_Target_1").  
                 Custom("email", "demo@harness.io").  
                 Build()  
      
        ctx, cancel := context.WithCancel(context.Background())  
  
         go func() {  
                 for {  
                        select {  
                         case <-ctx.Done():  
                                 return  
                         default:  
                                 showFeature, err :=     client.BoolVariation(featureFlag, &target, false)  
  
                                  if err != nil {  
                                        fmt.Printf("Error getting value: %v", err)  
                                  }  
  
                                  fmt.Printf("KeyFeature flag '%s' is %t for this user\n", featureFlag, showFeature)  
                      time.Sleep(10 * time.Second)  
                 }  
             }  
        }()  
  
        time.Sleep(5 * time.Minute)  
        cancel()  
}