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Choosing Mircoservice over Monolithic Architecture

By Jerry Gagliano

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I want to discuss the advantages of developing a microservice over a monolithic architecture and how I used mircoservices with my project. I won't get too deep technically, as I want to keep this simple for any skill level developer.

I recently implemented a newsletter subscription module on We want to allow users to subscribe to our newsletter for future news updates which will use a 3rd party service called MailChimp.

MailChimp, for those who don't know, it's a service that gathers emails and sends newsletters directly to your subscriber's email inbox. A newsletter subscription is an interesting marketing strategy to gather, attract users, and build a highly interested community in your product.

Overview Site Architecture is based on Next.js which exports only static files (HTML, CSS, and javascript). Which are deployed to Firebase Hosting. I wrote an article about this if your curious and want more details about it Featured Project -

The site has no communication with any server or is even rendered by a server. To implement this newsletter feature I needed the front-end to communicate directly to Mailchimp.

The Main Problem

Executing requests by the browser causes security errors called CORS Cross-Origin Resource Sharing. By default, browsers restrict cross-origin HTTP requests initiated from scripts. For example, XMLHttpRequest and the Fetch API follow the same-origin policy.

This means that a web application or site using those APIs can only request resources from the same origin (or same domain) the the application was loaded from.

Of course, I needed to rethink how to architect the site allowing me to communicate to MailChimp or even other 3rd party services for the future.

Choosing Between Microservice & Monolithic

Obiviously the two main choices that a developer is faced with are microservice or monolithic.

A microservice is an independent service that communicates over well-defined APIs. Microservices can be focused on specific modules or features for example:

  • Handling image uploads and resizing
  • Rest APIs. Returning simple json data structure
  • Authentication
  • Cron job tasks

In a monolithic architecture, all features or modules are tightly coupled and run as a single code base. One example, when a user clicks on a link, the page would fully render on the server generating HTML, CSS and Javascript which will be pushed to the client. Basically every action the user performs your server will execute. This is call Server Side Rendering (SSR).

You can read more about microservice vs monolithic

Developing The Microservice

To overcome this solution, I choose to develop a microservice. This microservice will contain just simple APIs that can communicate with 3rd party services or APIs providing data. It's small but will scale to handle all the back-end services.

Here is tech stack details I am using:

  • Node.js
  • Firebase Cloud Functions
  • Express.js (api routing)
  • GitHub and Actions (CI Builds and Deployment)

Firebase is my main environment and for most of my projects. I tend to use some of their features eventually. Will need implement authentication and Firestore for storing data.

Actual Microservice Implementation

Currently my mircoservice only contains subscribe newsletter route which is:

        // Express.js route"/subscribe-newsletter", subscribeNewsletter);

The Express.js route calls a module 'subscribeNewsletter' which handles the MailChimp API that sends the user's email.

        // Module called in the Express.js
        export const subscribeNewsletter = async (req: Request, res: Response) => {
            const {email} = req.body;

            // MailChimp keys are stored on the server side which is more secure.
            const AUDIENCE_ID = "***";
            const API_KEY = "****";
            const DATACENTER = "***";

            // ...will contain logic to make request to mailchimp

Here is an example of the front-end code when the user submits the email which will call the api route as you saw above '/subscribe-newsletter' from the microservice.

        // is my microservice domain
       	await fetch('', {
		body: JSON.stringify({
			email: inputRef.current.value, // email value from field input

		headers: {
			'Content-Type': 'application/json',

		method: 'POST',

The purpose of these example, is not to demonstrate how to implement MailChimp but more on how I architected this microservice.


On my side, the huge advantages of this project architected as a microservice.

  • Smaller code base: Developers can work independantly from the front-end.
  • Error Handling: In a monolithic architecture, if a single component fails, it can cause the entire product to fail. With microservices, only the request API will fail and not crash the entire website.
  • Faster Page Loads: Since the website and microservice are hosted on two separate servers. The microservice will execute only when a request is needed.
  • Cheaper Server Cost Fewer server executions, fewer costs. Cloud functions charge by the amount of usage.


As you can see, the architecture is separated layers from front-end to back-end. For experienced web developers this may be super easy but for non experience devs may need to wrap your head around.

In some cases, monolithic architecting could still be in favour and work well for certain developers or environments. A high percentage of sites or applications are architected as mircoservices.

If help or quick guidance for your site is needed, you can always contact me and will be glad to provide some pointers.

Thank you for taking the time in reading this blog. If you find any invalid information or want to add more this blog you may contact me at: