Implement LaunchDarkly with NodeJS from Scratch - Feature Flags

Implement feature flags in NodeJS with LaunchDarkly

🙋‍♂️ Shubham Verma 🗓 February 8, 2023

Implement LaunchDarkly with NodeJS from Scratch - Feature Flags

LaunchDarkly is a Feature Flagging and Experimentation Platform. LaunchDarkly provides very easy way to handle and launch the features to your users. It helps in A/B testing of the features. You can fundamentally change how you deliver software. Using LaunchDarkly you can innovate faster, deploy fearlessly, and make each release a masterpiece.

Here we are talking more about the feature flags. So let's discuss about the feature flags.

What are the feature flags?

The feature flags are basic server side flags that control the visibility of the feature to the users or for any other functionalities. This feature flags decide which part of the code should be run. It can be server side flag or client side flag.
Server side flag: If the flag is managed on server end then it is called server side flag.
For example:

                            const flag = true;
                            if(flag){
                                Do this
                            }else{
                                Otherwise Do this
                            }

Client side flag: If the flag is manages on client side then it is called client side flag.
For example:

                                        const isFeatureShow = true;
                                        return (
                                        <>
                                            {
                                                isFeatureShow && (<div>This is my feature</div>)
                                            }
                                        </>
                                        );

You can implement the feature flag and if the flag is true, the feature will show, if the flag is false, the feature won't show.
That's the kind of basic logic behind a feature flag. It enables you to easily change whether code will run and that way you can work on code without having issues.
You can do more than just simple on-off Boolean flags. You can do string flags and number flags and Jason object flags. That way you can pass configuration information and do multiple variations of flags. You can do a lot more powerful things and just say yes or no and run this code, yes or no show this feature.

Why do we need feature flags tools?

We have tons of benefits of using feature flags tools. Here are some advantages of using feature flags.

You can use flags to improve your development workflow as you want.
You can reduce merge conflicts by eliminating long-running branches. So I can be working on a feature and actually even merge my code back into the main branch on a regular basis without necessarily being concerned that that code is going to run and cause problems for everybody else.
You can test different scenarios without making code changes.
You can pass values from a flag and see how this is going to work without manual code changes. I can just go in and flip the flag or flip the variation and see what the effect is going to be. I can control the availability of in-progress features to specific users, groups, and regions.
Only allow our testing team to while A/B testing even in production so they're the only ones who see it.
Easy roll out the feature, You can roll it out to a beta list of users and they're the only ones who have access to it.
You can do all kinds of targeting of features of feature flags to particular users.
You can do a progressive rollout of a feature to prevent any problems. Only roll this feature out to 10 percent, 20%, and so on, until I'm sure that everything is stable. And that way, if there's any problem, I can just turn the flag off, and roll it back, which is the big thing. I can kill a problematic feature without having to do a full rollback or redeploy. I can just flip that flag and the feature is turned off. Problem solved.

Let's implement the LaunchDarkly with NodeJS

Here we will use LaunchDarkly to control the feature flags and we use this feature flag to enable and disable the for specific users.

Step 1: Sign Up on LaunchDarkly

To use the LaunchDarkly, we need to register ourself using this below link. Link is given in the bottom of the article.

Implement LaunchDarkly with NodeJS from Scratch - Feature Flags

Step 2: Create Environment on LaunchDarkly

If you don't have any environment on your launchdarkly then create an environment like development, test, local, alpha, beta etc under your project.

Most probably you should have two environments "Test" and "Production". We will use "Test" environment for this tutorial.

Implement LaunchDarkly with NodeJS from Scratch - Feature Flags

Step 3: Create Your first feature flag on LaunchDarkly

Now we need to create a feature flag. Let's be in the same page and create a feature flag with key my-boolean-flag with the same value my-boolean-flag.

Implement LaunchDarkly with NodeJS from Scratch - Feature Flags

Now you can see you feature flag is created and ready to use.

Implement LaunchDarkly with NodeJS from Scratch - Feature Flags

Step 4: Get the sdkKey of your feature flag from LaunchDarkly

Now, you need to get the sdkKey from your LaunchDarkly. You can get it from below path.

Account settings -> Projects -> CHOOSE YOUR PROJECT -> Copy the correct environment's SDK Key and store it. This will be used when we will create our server or client

Implement LaunchDarkly with NodeJS from Scratch - Feature Flags

Now its time to create our Node Server

In this section we will create a NodeJs server and implement an API to fecth the feature flag of the LaunchDarkly and display our feature based on the feature value.
Further we will add a rule in our LaunchDarkly. This rule will enable the feature flag for only selected users. When those selected user will try to access those feature, the feature will be enable only for those user wha has permission granted or fullfil the rules.
This going to be very interesting.

Step 5: Create Node server using Express Application Generator

Express Application Generator can help to generate the project scaffolding for our node app with necessary routes and view templates like jade. So, to create the node project scaffolding run the following commands one by one.

mkdir launchDarkly

cd launchDarkly

npx express-generator

Implement LaunchDarkly with NodeJS from Scratch - Feature Flags

npm install

npm start

The above commands will make a folder with the name launchDarkly and create all the necessary files in it. and the npm start command will start the server you can check the server is running by opening the URL localhost:3000 in your browser.

Implement LaunchDarkly with NodeJS from Scratch - Feature Flags

Now we have created our server, now let's integrate LaunchDarkly and its feature flag in our node application.

Step 6: Integrate LaunchDarkly in NodeJs App

Now it's time to integrate the LaunchDarkly in our NodeJs app, for this create a file launchDarkly.js in your root directory.
In this file, we will create and export a method getLdFalg(), in this method, we will initialize the LaunchDarkly using the launchDarkly SDK ie. "launchdarkly-node-server-sdk".
Now go to your directory, create the file, and write the below codes. We will use this file in our API while enabling/disabling the feature for users.

Don't forget to update you LaunchDarkly's SDK key in this file.

File: launchDarkly.js

                    
                                                const LaunchDarkly = require('launchdarkly-node-server-sdk');
                    
                                                module.exports = function getLdFalg(featureFlagKey, userId) {
                                                    return new Promise(async (resolve, reject) => {
                                                        const sdkKey = 'sdk-XXXXX-XXXX-XXXXX-XXXXXXXXX';
                                                        if (sdkKey == "") {
                                                            console.log("Please add your SDK_KEY");
                                                            process.exit(1);
                                                        }
                    
                                                        const ldClient = LaunchDarkly.init(sdkKey);
                                                        ldClient.waitForInitialization().then(function () {
                                                            console.log("SDK successfully initialized!");
                                                            const context = {
                                                                kind: "user",
                                                                key: "example-context-key",
                                                                // name: "Shubham",
                                                                email: userId
                                                            };
                                                            ldClient.variation(featureFlagKey, context, false, function (err, flagValue) {
                                                                console.log('flagValue :', flagValue);
                                                                ldClient.flush(function () {
                                                                    ldClient.close();
                                                                });
                                                                return resolve(flagValue);
                                                            });
                                                        }).catch(function (error) {
                                                            console.log("SDK failed to initialize: ", error);
                                                            resolve(false);
                                                            process.exit(1);
                                                        });
                                                    });
                                                }

Step 7: Create an API endpoint

Now we need to create an API endpoint, we will use this endpoint to control the feature. This API will help us to provide the information to display the feature to specific users or not.
This API will render a view engine (jade in this app) with some information.
For this, you need to update the code in the file routes/users.js with the following codes.

File: routes/users.js

                    
                                var express = require('express');
                                var router = express.Router();
                                const getLdFalg = require('../launchDarkly');
                    
                                router.get('/:userId', async function (req, res, next) {
                                    const userId = req.params.userId;
                                    const featureFlagKey = "my-boolean-flag";
                                    getLdFalg(featureFlagKey, userId).then((value) => {
                                        res.render('index', { title: `Hello ${userId}`, featureFlag: value, userId: userId });
                                    });
                                });
                    
                                module.exports = router;

Step 8: Prepare your views

Now we need to prepare views to display the feature to the users. For this we need to update the file views/index.jade, in this we will design our views beautifully. You can design as per your choice and you can create your client application in React, Angular, or any client-side technology to display the feature.
Here we are using jade as a template engine which comes default with express-generator.

So let's update our file views/index.jadewith the following codes.

Please note that you need to maintain the formatting of the jade file for smooth working For your help I am adding the image of the codes also.

File: views/index.jade

                                extends layout
                    
                                block content
                                div(style="width:50%; border:2px solid gray; margin:10px; padding: 10px;")
                                    div(style="width:50%; margin: 0 auto; padding: 20px;")
                                    h1= title
                                    h3 Welcome to LaunchDarkly
                    
                                    div(style="width:100%; margin: 0 auto; padding: 10px;")
                                        if featureFlag
                                        p(style="color:green;") You have access to see the below feature
                                        img.image( style= "width:300px;" src='https://idkblogs.com/images/refresh/1645286866379.jpg')
                                        else
                                        p(style="color:red;") You dont't have access to see the below feature

Image File: views/index.jade

Implement LaunchDarkly with NodeJS from Scratch - Feature Flags

Step 9: Turn on your LaunchDarkly flag

Now, we need to turn our flag from LaunchDarkly, to do so, go to LaunchDarkly and turn on your feature flag, also don't forget to save your changes.

Implement LaunchDarkly with NodeJS from Scratch - Feature Flags

Step 10: Restar your node server

It's time to restart the server bur "npm start" command and hit the URL "/users /[email protected]" in your browser and see the changes.
You can see your feature is showing.

Implement LaunchDarkly with NodeJS from Scratch - Feature Flags

You can check with different-different emails in the URL, and you can see it showing for everyone.

Step 11: Turn off the LaunchDarkly flag

Don't restart the server.

Now go to LaunchDarkly and turn off the feature you can check with different-different emails in the URL, and you can see the feature is NOT showing for anyone without any code change or withour restaring the server.

Implement LaunchDarkly with NodeJS from Scratch - Feature Flags

Step 11: Add a rule to control the feature visibility for some specific persons

Currently, this feature is either enabled or disabled for all users, this will not solve our problem, we want to give access to only some users who have privileged access. Or want to give access to some group. To achieve this we need to define the rule for this flag. We can add rules in LaunchDarkly. So let's do this.
Go to LaunchDarkly and add the following rules under rules section.

Current Rule: email is one of [email protected]

Implement LaunchDarkly with NodeJS from Scratch - Feature Flags

We have added a rule, in this rule, we are allowing only the person who has the email [email protected] in the URL can access this feature, No one can access this feature rather than [email protected].
You can add more emails, usernames, names, etc in your rule.
So, as per our rule:

Allowed URL:
/users/[email protected]

Not allowed URL:
/users/ [email protected]
/users/ [email protected]

Step 12: Play with rules

I would recommend you to please add, remove, update the rules, and play with it.

Conclusion:

In this article, we learned the following things:
What are the feature flags?
Why do we need feature flags tools?
Implementation the LaunchDarkly with NodeJS
Create Your first feature flag on LaunchDarkly
Get the sdkKey of your feature flag from LaunchDarkly
Create Node server using Express Application Generator
Create an API endpoint
Work with template engines like Jade and how to do styling in Jade.
How to render html from the server side.
Add a rule in LaunchDarkly to control the feature visibility for some specific persons

Links

LaunchDarkly Registration

Related Keywords:

Implement LaunchDarkly with NodeJS from Scratch

Implement LaunchDarkly with NodeJS

What is feature flags and how it works

What is LaunchDarkly

LaunchDarkly and NodeJS

Feature flags for Node.js - LaunchDarkly

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