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Microservices Versus Serverless

The Kalix Team at Lightbend
  • 1 Jan 2023,
  • 7 minute read


Monolithic architecture has long been one of the most common software architectures, working exceptionally well in the early days of software development. However, its structure can severely limit its use in the modern development sphere—especially in the face of cloud computing.

Cloud computing has seen exponential popularity growth, resulting from its flexibility, maintainability, and speed of delivery. The ever-growing need for a more efficient and reliable software delivery model drives us to shift away from large, monolithic applications to the various emerging cloud-centric architectures.

Two such cloud-driven frameworks are serverless and microservices architectures. These adaptable models provide businesses with the agility, flexibility, and scalability to meet changing market demands.

Serverless or Microservices: Which Is Right for You?

Applications that use monolithic architectures require that all services and functions be tightly coupled to a single unit and, usually, a large codebase. As a result, accommodating the scaling needs of a single process has required scaling the entire system. And as our application’s codebase grows, adding or improving features becomes more complicated, an update requires redeploying the entire application.

Engineers experienced this flaw in monolithic architecture and developed microservices and serverless approaches to decouple these large applications into logical components and separate their code bases into independent services. Both solutions function on the same fundamental concept—prioritizing scalability and flexibility by dividing large systems into smaller components. The result is dramatically simplified development, deployment, and maintenance processes.

While born from the same need, serverless and microservices architectures are distinct technologies that differ significantly and fill different roles in modern software development.

What Are Microservices?

Microservices architecture is a way to build software by structuring it as a set of loosely coupled services deployed independently and communicating using APIs. This technique involves dividing large applications into smaller, functional autonomous components that can act independently and communicate with one another to exchange data.

These units are called microservices because each service is deployed within a container that operates as a standalone application with dedicated resources (a database). Moreover, each unit is responsible for a specific process or function that contributes to the overall operation of the application.

For example, an e-commerce application built using a monolithic architecture would typically have many services coupled into a single unit. But in a microservice architecture, these services are broken into independent services that may consist of a service that authenticates users, a search engine service that searches a product database based on user-generated queries, a checkout service that processes payments, and so on. All of these services are then assembled and connected via APIs to communicate with each other.

Benefits of Microservices

There are several benefits to using microservices, including:

  • Separation of concern—Microservices offer a clear separation of concern, as a dedicated team is often assigned to develop and maintain each service. This ensures each service is distinct.
  • Diversity in technology stack—Microservices allow us to choose virtually any language, framework, or data store for each microservice—or any technology stack best suited for each specific microservice's requirements.
  • Reliability—Microservices are resilient. If one of the services goes down, it doesn’t affect the entire application because other services aren’t reliant on the affected service and will usually continue functioning.
  • Scalability—Each service in a microservices architecture can scale independently according to resource usage and load requirement.
  • Reusability—Services are self-contained, making them incredibly adaptable and reusable.
  • Flexibility—Microservices allow the development, testing, and deployment of services independently without interfering with other services or the parent application.
  • Isolation—Isolation of services makes diagnosing faults within larger applications easy.

Disadvantages of Microservices

Although microservices are beneficial in many ways, there are challenges we should be aware of as well, such as:

  • Complexity—As the number of components or services increases, microservices acquire the complexities of distributed systems, making them difficult to manage.
  • Difficulties testing—Testing is difficult because every microservice must be tested independently.
  • Debugging is complicated—Debugging issues in a microservice architecture can be challenging because each service has an independent log file, increasing the labor necessary to examine every log.
  • Security concerns—For the software to function, each service must communicate externally via an API. Each communication passage increases the number of points at which the application is vulnerable to attacks.
  • Overhead and more resources—Since every service is decoupled, there’s an increased overhead of managing multiple databases, which requires data consistency and microservices expertise.

What Is Serverless?

Running an application typically requires a virtual or physical server. Therefore, a managed server infrastructure is usually necessary to host a software application on the Internet.

Contrary to the implied meaning of serverless architecture, serverless enables us to focus on the actual application—not the server infrastructure.

Serverless architecture relies on cloud providers to handle many aspects of infrastructure management for us, allowing us to concentrate more on our development tasks instead of provisioning and maintaining servers.

Instead of deploying services like in a microservice, we have to deploy functions, which are executed based on events or triggers like HTTP requests. As a result, the provided server is only used when an application function is triggered and the server allocates resources to it. After this function completes, the server resources are withdrawn. So, we only pay for the periods when the app runs the serverless functions.

There are two main concepts in a serverless architecture:

  • Back-end as a service (BaaS)—This serverless model offers pre-built features so the developer can outsource back-end aspects of an application to the cloud provider while focusing on writing and maintaining the front end (AWS Lambda).
  • Function as a service (FaaS)—This model gives developers the complete flexibility to create fragments or modular pieces of code, which will be executed on-demand as events occur on the back- or front-end of the application (Cloudflare Workers).

Benefits of Serverless

The benefits that serverless offers us includes:

  • Reduced complexity—Since it’s the vendor's responsibility to build, maintain, upgrade and manage all computing resources, our development experience is far less complex.
  • Flexibility—Serverless architecture breaks applications into serverless functionality that’s easy to deploy and manage independently.
  • Reduced cost—Since serverless functions only execute when triggered and otherwise remain idle, they experience much lower cloud computing costs than those incurred when permanently running servers. We only pay when our code is executed.
  • Scalability—Serverless provides the flexibility to scale resources whenever there’s a specific need and to shrink when peak time ends. Moreover, its modularity means that we can automate application scaling and incrementally add new functions.
  • Reliability and decreased latency—Compared to traditional infrastructure, public cloud vendors have data centers worldwide, thereby reducing request/response latency and downtime issues.

Disadvantages of Serverless

Some disadvantages to using serverless include:

  • Less customization—There are limits to our options for configurability and customizing back-end infrastructures like CPU power or RAM limits. We can only run functions on what the service provider offers.
  • Reliance on third parties—Extensive reliance on third-party cloud providers tasked with managing our serverless functions can add operational and troubleshooting time.
  • Cold starts—A function that has been inactive for an extended period may require a cold start to operate again, as it might have been removed from the system’s cache. This then requires additional time for resources to initialize.
  • Stack limitations—We may have to code functions using the languages, frameworks, and tools our provider supports, which can also make switching providers another concern.
  • Short-term operation—Serverless architecture is suitable for only short real-time processes.

Microservices Versus Serverless

The shared agility of microservices and serverless can lower operational costs and significantly reduce time-to-market, easing the development process and the effort of managing changing requirements.

Due to their complementary characteristics, both microservices and serverless can be combined into a technology stack to leverage the benefits of both architectures. It’s also possible to build a microservice by combining smaller modules of serverless functions, which will execute only during certain events in the microservice.

So even though they are different technical architectures, they can be implemented as complements of each other. We can quickly build different microservices in various languages that consist of several serverless functions as components and are connected to communicate via API.


The recent shift from monolithic to cloud-based architectures has led to a new paradigm for the deployment of applications. Microservices and serverless architectures make it possible to quickly develop agile and flexible software, enabling businesses to stand out in an increasingly competitive technological landscape, which is why services like Kalix have become so in-demand.

Using microservices as long-term solutions allow us to constantly scale, while serverless computing is better aligned with event-driven, short-term, asynchronous operations. However, the two architectures are not mutually exclusive. In fact, microservices and serverless functions complement one another to form a robust and flexible development solution, meaning there’s no need to choose between them.

Kalix from Lightbend is an excellent example of combining these technologies to create something that is more than the sum of its parts. Kalix leverages microservices to offer you a serverless environment with no operations required. It works with any back end, allows you to work in your own language, and is exceedingly cost efficient.

Learn how Kalix can help you transform your product’s capabilities.