Monolithic vs. Microservices Architecture: A Side-by-Side Comparison
Microservices have gained a lot of traction in the last few years.
Ever since the dawn of time, monolithism – packaging all your modules into one colossal codebase – was the default way to go when building software applications. However, as applications have had to cater to increasing volumes (of millions) of users over the internet over the last decade, scalability and flexibility have become ever more critical. As a result, microservice-based architectures have taken the software industry by storm.
In this post, we’ll compare them against the conventional monolithic way of building software.
We’ll discuss monolithic applications and how they emerged to be the default way of doing things. We’ll talk about their strengths, followed by the many disadvantages that led to the now-famous microservice architecture. We will then compare this with how microservices are structured, discuss an example, go through their pros and cons, and eventually conclude on which of these would be the right fit for your application and your business.
Here’s an outline of what we’ll be covering so you can easily navigate or skip ahead in the guide –
- What is a Monolithic Architecture?
- What is a Microservices Architecture?
- How a Microservices Architecture Is Structured
- Example of a Microservice Architecture
- Advantages of a Microservices Architecture
- Which Architecture is Right for Your Business?
- Wrapping it Up
What is a Monolithic Architecture?
A monolithic architecture has all of the application’s functionality and services dumped into one massive codebase.
The English word “monolith” refers to a large ancient block of stone. In the same spirit, a monolithic application refers to an enormous centralized block of code that contains the entirety of your full-fledged, full-stack application with all its functionalities tightly coupled with one another. Moreover, it wouldn’t be totally unfair to call this style of software development (especially for heavy applications) somewhat ancient.
Since the dawn of time, monolithic architectures have emerged as the default way of building software. Regardless of its different tiers, an application was thought more of as one project — one entity; and this unification also made its way to the code level. It is quite probable that the first full-fledged programming app you built also had all of its pieces bundled into one large executable. We’ve all defaulted to monolithic approaches at one point or the other when we started.
However, monolith architectures have started to earn a bad reputation since the last decade or more and broadly give an impression of a less intelligent, thoughtful, and efficient way of building large-scale applications.
This can be attributed to their tight inter-component coupling, lack of modularity, consequent fragility (vulnerability to minor issues), hefty resource footprints, and inefficiency in scaling, managing, and maintaining. Before we dive deeper into the several drawbacks of monoliths, along with their considerable strengths, let’s get a lay of the land of their anatomy.
How a Monolithic Architecture Is Structured
Most conventional applications (monolithic or microservice-based) broadly consist of three major components –
Server-side: This is the back-end of your full-stack application – the part of your codebase that contains the business logic – the secret sauce of your product. The server-side layer also serves your application’s UI and web pages, along with taking care of authentication, authorization, routing, state management, caching, etc.
Database: The database, perhaps the most straightforward component here, stores user data relevant to your service; for example, user information, passwords, preferences, transaction history, etc.). This layer usually also includes the server-database interface that queries from the database.
In a monolith application, you have all three components stuffed into one unit – the front-end code with the fancy UI, the back-end that serves these web pages, and the database that stores all user data.
Advantages of a Monolithic Architecture
Even though the structure of this article might suggest that all the glory lies in the microservices way of doing things, there are certain benefits to monolithism.
Building software monolithically gives you more of a sense of control – to have everything under one big umbrella – often under one parent folder might seem more easily understandable, navigable, manageable, and maintainable. If not carefully considered, it feels like the default way of doing things; and, therefore, doesn’t require any additional expertise.
This ease of development reflects mainly for small-scale applications where there’s not much going on. There’s no need to configure and set up APIs for any inter-component communication; all the modules can talk to each other by being hosted on the same instance, next to each other. For example, you wouldn’t benefit from excessive division and distribution of the layers of a simple, static user portfolio website; it might even be detrimental to microservice things here.
Easier deployment, tracking, and monitoring
Coming to deployment, as you can imagine, it is much easier to ship stuff (not just software) as one complete package instead of as its multiple individual constituents. Once you’ve got everything set and working, all you have to care about is the deployment of one executable – if it goes well, great!; if not, you make amends and retry. This is much more convenient than toiling through multiple deployment pipelines – one for each module in your application, especially for small teams.
To put it simply, any update to a monolithic application might require you to prepare and ship only one chunk of deployable code instead of ensuring the smooth delivery of updates across multiple microservices.
Along similar lines, it is more tractable to track the issues and performance of one deployment – to have all the metrics you need to evaluate performance in one place, instead of having module instances all over the place.
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Easier end-to-end testing and debugging
An integral component of the deployment pipeline is the testing suite that ensures your application is error-free before going live. Because testing is a non-negotiable prerequisite to shipping, monolithic apps are also advantageous during testing regimes before deployment.
Closely knit application modules in monoliths are quicker and easier to test end-to-end and subsequently debug when issues arise. This is because end-to-end testing on one executable is faster than when spread across microservices.
In monolithic apps, you run the tests once, get errors about these issues that are easy to find (by being in the same, combined codebase), make necessary fixes, hit the launch button, and are good to go. On the other hand, with microservices, you need to test your whole application end-to-end each time an independent module is deployed and be on the lookout for issues across multiple iterations. This multiplies the required effort.
Lower Latency due to reduced Inter-Service Network Communication
Since the different layers of an application are combined and hosted as one entity (directory or file), intra-app data transfer is relatively quick because most of everything is usually available on the same compute instance.
This is in stark contrast to microservices, where you might need to make dozens of API calls just to populate one web page – which can bring network limitations into the equation and potentially slow things down and affect performance.
As you might have noticed, most of these strengths above stem from the principle of handling your application as one unified entity. It also seems evident that this method turns out to be advantageous primarily for small-scale setups – where splitting functionalities across different (micro) services might either get out of hand (for small teams) or be outright overkill (for small applications).
However, adhering to this very principle of unification also has several caveats, which we briefly hinted at before. Let’s go through these.
Potential Drawbacks of a Monolithic Architecture
As applications scale to become the behemoths we see these days (e.g., Facebook, Instagram, Twitter, etc.), or even mid-scale applications, following monolithic patterns can quickly get out of hand and lead to chaos. Your project can very soon become a big ball of mud — a term used to (very vividly) define ‘a haphazardly structured, sprawling, sloppy, duct-tape-and-baling-wire, spaghetti-code jungle’.
Therefore, it is worth noting that most of the disadvantages mentioned below apply to applications and organizations that are mid to large in scale.
Compromises Comprehension and Makes Onboarding Challenging
Human memory is limited. As the size of your indivisible codebase increases, your grasp on the inner workings of your application weakens.
As you continue to dump more and more functionality into this one project, it eventually swells up to the extent that the whole setup goes beyond the understanding of one individual, i.e., no one individual can have a clear account of the entirety of the stack.
Moreover, this makes onboarding new developers even more difficult. Regardless of the sub-module they are handling, new team members also need to get acquainted with the enormous code base; because of how tightly coupled each part is to the rest of the application. You want your recruits to start contributing to the project right away. This, however, slows things down, inhibits progress, and lowers team morale.
Lack of Flexibility – Painful Renovating / Upgrading of Technology Stack
At the current pace of development of programming languages, web frameworks, libraries, and technologies, one wouldn’t be surprised to find even the most popular ones going obsolete in the span of a few months. As a result, organizations that can’t adapt and change directions quickly will suffer, while others that take the change in their stride will flourish.
The former is the likely fate of most monolith applications. Due to their very nature, monolith applications are composed using a single tech stack. This imposes several constraints on the things you can get done or the kinds of architectures or paradigms you can adopt when updating your application.
Due to the tight coupling between different software modules in a monolithic app, you can’t just pull out one module, integrate updates into it, and fit the piece back into the block. Even one slight upgrade will also require very many changes across the codebase. It might even necessitate rewriting the whole thing from scratch, especially when switching to a different framework (for instance, one that is better suited for some of the functionalities or their business needs). These disruptions set back development significantly and reflect a lack of operational agility. On the other hand, more modular and flexible applications will take much less time to make changes and reap the benefits.
Expensive with a High Resource Footprint
Modules in monolithic apps don’t exist as independent units and are closely tied to the rest of the application. As a result, to cater to large traffic volumes, even if one module requires more compute, you will have to allocate more resources to the whole project. You can’t just scale one component, only the entire application. This leads to unnecessary expenses and doesn’t allow you to make the most of horizontal scaling (adding more machines/nodes to your pool of resources).
Besides, every change (small or big) in any part of the code requires a complete redeployment. This can be pretty expensive in terms of time and resources – requiring the whole thing to be re-built, tested, and shipped for every change. This also contributes to slowing down build and release cycles eventually and hindering growh.
Imagine having to wait for thorough and elaborate CI (continuous integration) checks designed for the whole application when the only change you pushed was a single-line comment in one tiny module.
Fragility – Vulnerability to Small Issues
One of the most significant issues with monolithic applications is their fragility in the face of minor issues – even one small bug can quickly bring down the whole application. Just like the other drawbacks with monoliths, this one also stems from the tight inter-component coupling.
By nature, each change you make to the code influences the whole stack. This means that a bug in one part of the system can take down the entire application at once (as opposed to impacting just one module of the whole) – making your system a whole lot more vulnerable.
Having read about the many caveats with monolithic software projects, it is not difficult to imagine what a (contrasting) microservice realm broadly looks like and what it has to offer. Let’s dive in.
What is a Microservices Architecture?
A microservices architecture decomposes an application into a collection of singular, independent, reusable modules that take care of a different service aspect.
In the last few years, the world has shown a tremendous interest in decentralizing and distributing things – not just application development-wise, but for currency, user data, the internet, and more. This speaks to the virtues of decentralizing services as a philosophy, suggesting the superiority of this approach.
Microservices are essentially multiple subunits of a larger whole (the application) that operate independently (with one another) and take responsibility for different parts (services) of your project. In programming terms, you can see the following principles in action in how microservices operate –
- Modularity: The idea of breaking down an application’s functionality into smaller, reusable components.
- Encapsulation: The process of packaging a module’s state and behavior so that the internal design and implementation of the (micro) service stays hidden from the rest of the application. You can read more about encapsulation in programming paradigms in this post on our blog.
- Divide and conquer: The algorithm design principle that advocates that you tackle any problem by dividing it into multiple smaller (atomic) problems – till the point that they become simple enough to be directly solvable.
- Single Responsibility Principle (SRP): This is the first of the S.O.L.I.D programming principles that assign each class, function, or module with only one responsibility – one single purpose. You can read more about the rest of the principles in this post on our blog.
As you can see, all of these are quite related and complementary to each other. Now let’s look at how microservice applications are architected, followed by a dummy example.
How a Microservices Architecture Is Structured
As opposed to all the application components bundled into one monolithic chunk, microservices split up application functionality across multiple channels.
Each of these microservices encapsulates an implementation of an application’s service and becomes the single digital touchpoint for accessing it. They are independently deployable and communicate with one another through custom APIs (usually HTTP-based). Moreover, the loose coupling allows each microservice to be reusable in multiple contexts – even across multiple applications and businesses.
Consequently, this architecture also allows for flexibility in updating and scaling individual modules without worrying about any unexpected consequences to the rest of the application. To get a better sense of this architecture, let’s discuss a dummy microservice-based application.
Example of a Microservices Architecture
Take the example of an e-commerce application. If you were to split its workings into multiple services logically, the following is what it might broadly consist of –
- User/account information service – For taking care of account information, such as – user data, preferences, previous orders, etc.
- Inventory service – For keeping track of product stocks in the inventory.
- Shipping service – For handling information about different shipping options.
- Payments service – For conducting financial transactions (purchases, refunds, etc.) online.
Each of the microservices will take care of one responsibility in an independent way.
Now that we have a decent sense of what compartmentalization looks like in practice, let’s discuss the pros of this approach and understand why tech giants like Google, Netflix, Amazon, etc., have been leading the transition to micro-services.
Advantages of a Microservices Architecture
From the description so far, the advantages of microservices seem pretty straightforward. Regardless, let’s list them in bullet points.
Modularising your application and its code allows you to work with these independent modules in different contexts. You can reuse these modules in different services and across various applications. However, imagine these functionalities entangled into a complex codebase, as in monolithic applications. In that case, their services are available (and restricted) only to that chunk of code and aren’t reusable elsewhere.
For example, you can reuse a payments microservice across different applications for your business. In the monolithic case, however, you’ll have to rewrite the logic for the other app, and as a result, introduce redundancy.
Footnote: Interestingly, Don’t Repeat Yourself (DRY) is another one of the S.O.L.I.D programming principles (we discussed before) that advocates the idea of reusability. Microservices seem to be doing justice to many of these principles.
Each of your microservices can be independently scaled – both vertically and horizontally. As user traffic volumes vary, compute requirements across services may change. Because each microservice is independent and takes care of a different part of your application, you can scale up parts that need more attention and downscale others that don’t.
This is in stark contrast to monoliths, where you can’t scale just one part – you either scale the whole application, or you don’t, which, as we discussed, can be pretty inefficient.
Cost, Resource, and Time Effective
Having more control over how you fine-scale your infrastructure for user traffic (as seen in the last point) also saves your organization a lot of money. You only need to invest in resources for microservices that are getting a lot of traffic, and you can save on those that are not.
Additionally, shorter build times, test cycles, and overall deployment pipelines save your organization a lot of time because of only having to ship individual microservices (instead of the whole app each time). This means that new features roll out faster, along with high operational agility, and consequently, team morale.
More Robust and Easier to Maintain
Thanks to the loose inter-component coupling, a bug in one microservice affects only the code within the confines of that very microservice. Therefore, an issue local to a microservice doesn’t propagate and wreak havoc across the whole application.
Besides, once identified, fixing the issue is as easy as pulling out the erroneous module, making fixes, and pushing it back online – a luxury we couldn’t enjoy within monolithic spaghetti code jungles.
Because these modules operate independently, there is no restriction on the choice of tech stack – the frameworks, libraries, and sets of tools that the team can employ to develop stuff. So long as the microservices can effectively communicate with one another through lightweight, universal protocols (e.g., HTTP), it doesn’t matter which development stack you use for which service.
This allows organizations to choose from varying tech stacks and cherry-pick the ones that best suit each of their microservices’ business requirements; instead of relying on one stack for everything (like in monoliths).
Easier to Understand
And finally, microservice architectures are easier on the brain. They make more sense logically (especially for large-scale applications) and are easier to grasp, conceptually visualize, and work with. As a result, new developers on the team can get onboarded quickly, understand the microservice assigned to them, and get a lot more work done.
Potential Drawbacks of a Microservices Architecture
For all the positives they bring to the table, microservices also have some drawbacks and therefore aren’t the one size that fits all.
Complexity, Overkill for Small Applications
Despite all of their benefits, microservices do introduce some complexity into the system. This involves carefully setting up the inter-service and database connections, coordinating them, managing multiple deployment pipelines, etc.
Even though these efforts might pay reasonable dividends for enterprise applications, small-scale projects wouldn’t have much to gain from this divide and conquer approach and might even incur losses.
Difficult to Manage for Small Teams
The inherent distribution in the system and the concerted effort required to handle it effectively can take a toll on small teams, as they may not always have the specialized personnel and resources to address the breadth of requirements.
Because all microservices are deployed independently and communicate over the internet, network latency can slow things down. If not implemented correctly, this can become a real bottleneck for the performance of large-scale applications.
Testing and Monitoring
As we discussed previously, running end-to-end and integration tests on independently deployed applications is much more difficult. Along similar lines, monitoring the performance of a distributed set of services – their health, downtimes, request/response rates, bottlenecks, can become tricky to manage.
Which Architecture is Right for Your Business?
Now that we’ve seen the two architectures side-by-side and discussed their pros and cons, how does one decide which approach suits their business requirements better? To answer this question, it helps to think about the following three factors –
- Your application’s size
- Your organization’s size
- Your team’s expertise with microservices
When to Choose a Monolithic Architecture
One easy conclusion that emerged from the drawbacks of microservices (we saw above) is that microservices might do more harm than good for smaller-scale setups. If you’re limited by your application, developer team, and/or microservices expertise, then monolith applications will be easier to run and manage with more benefits.
If you are a small group, you don’t need to jump on the microservices bandwagon.
When to Choose a Microservices Architecture
However, if you want to build a large-scale, enterprise-level application (or one that eventually scales to that), investing in a microservices architecture will pay enormous dividends for your business. It is important to note that when you start developing software, doing things the monolithic way might seem easier, but the microservice route will lead to efficiency and scalability.
Footnote: Adopting a monolithic architecture might be helpful up to a particular (application) scale. But beyond that, once your application becomes sufficiently big, sticking with a monolith architecture is going to be detrimental. However, transitioning to microservices is bound to pay huge dividends – for all the reasons we shared in the pros section.
Wrapping it Up
In this post, we did a deep dive into monolithic and microservice application architectures. We looked at how they are structured, discussed a few examples, listed their pros and cons, and finally concluded by helping you choose between the two.
Now that you have a good picture of the two architectures, think about which better suits your application and business requirements. Would you rather have all your service implementations dumped into one codebase, or would you split things up into microservices?
Once you are done deciding that and need to think about ways of boosting your application’s performance, make sure to check out Scout’s APM tool. Get live alerts about your application bottlenecks, memory bloat, leaks, slow database queries, real-time performance insights, and much more. Get started with a 14-day free trial (no credit card needed)! Also, check out our blog for more software programming and web development content.