How to develop a scalable web service

Scalability is one of the most important conditions for the successful operation of a web service. This article will describe the main criteria for meeting this condition:

• what can limit the structure of a resilient and scalable web service;
• which technologies will allow the scaling idea to be implemented;
• how to develop a web service capable of handling a large number of visitors at the peak of success and seamlessly accommodating feature expansion at any stage of development and operation.

Where to begin developing a scalable web service? To better understand the basic principles and highlight the advantages of this approach, you need to consider certain concepts, service architecture types, and popular frameworks.

Why is scalability needed?

Leading companies' websites must withstand enormous loads. Additionally, high performance and ease of operation of applications, web services, and websites are extremely important for a company's success.

Beginners who start developing web services and applications are often unaware of some problems they will encounter later:

• an increase in the number of visitors reduces web service performance and increases the bounce rate;
• expanding the product assortment negatively affects page load time; updating the online store catalog becomes problematic;
• changing the code structure becomes risky and complex; adding a new product or service will require a lot of time and financial costs, and the ability to conduct A/B testing is reduced.

As a result, if the problems are not resolved, the entrepreneur or web service owner loses opportunities, and limitations persist.

Do all web services encounter such problems during development and later?

To some extent, most of them are subject to certain threats. However, the degree of complexity depends on how well the web service was designed from the very beginning.

Scalable development is not a special kind of development. It is a set of principles and methods that help develop a web service according to high standards.

By following certain rules of web service development, you will be able to:

1. reduce page load time, error count, time for changes, and update cost of the web service;
2. improve user experience;
3. extend the lifecycle of offered products and services;
4. as a result, sales rates and brand loyalty increase.

Definition of the term «scalability» in web service development

The definition of web service scalability in development is the ability of a system, network, or specific process to handle an increased load when resources are added (often related to hardware).

Scalability is evaluated by the ratio of the increase in system performance to the increase in the number of resources used. Additionally, scalability implies the ability to add additional resources while preserving the structure of the central node.

If the system's scalability is poor, adding new resources leads only to a slight increase in performance, and after reaching a certain threshold, resource addition does not bring the desired effect at all.

In addition to scalability, there are a number of related concepts that help better understand the problem. One of them is recoverability. The term implies the ability of the system to restore functionality after a failure. This concept is closely related to the concept of the saturation point.

Saturation point is a certain degree of workload intensity at which the developed service begins to fail. Unjustified spikes in system operation typically lead to failure.

Under normal conditions, program performance changes proportionally to the load, which gradually increases. If at some point predictable growth is replaced by abnormal spikes, the saturation point has been reached.

Testing aimed at determining this point is called a scalability test. This helps determine reliability and scalability in web service development, as well as identify problem areas that hinder the efficient operation of the entire system.

What characteristics affect web service scalability?

1. Architecture. One of the most important components of web service scalability.
2. Framework overhead. Sometimes scalability is limited by the framework, so its choice affects application performance as the number of functions increases.
3. Robust code design. Code quality also significantly affects scalability.
4. Robust testing. With proper load and performance testing, you can find and eliminate vulnerabilities in web service development and ensure smooth growth.
5. Hardware limitations. Not only software affects scalability.
6. Integration of third-party components. The most common cause of problems and failures.

Scalable Application Architecture

Next, we'll discuss how to develop such a web service.

Frontend and Backend

The frontend is the visible part of a web service with which the user interacts directly. In software configuration, there can be many levels between hardware and the end user. Each of these may also have a frontend and backend.

The frontend is an abstraction that provides a user interface. For example, open a new browser tab, enter the address of a website, and press Enter. The site should load instantly. A well-designed page template is clear, and the visual component should be eye-catching, easy to understand, and convenient to navigate.

However, besides ease of use, a properly designed web service frontend also helps avoid scalability issues in the future.

Backend refers to everything that happens on the server. It interprets everything the user does in the frontend, passes it to the database if necessary, and sends a response back to the browser. This part takes up to 80% of the entire code and has the greatest impact on performance in web service development.

Backend is responsible for dynamic processes on the page and managing information storage, which can lead to issues. Backend can be built on any feature-rich programming language such as Javascript (Node.js), Python, PHP, C#, etc.

Multi-tier Scalable Web Service Architecture

A multi-tier model is a software model that must contain three components: a client, an application server to which the client application connects, and a database server to run the application.

Each tier of such a developed web service should perform only the most important functions, thereby significantly improving performance and scalability.

A multi-tier architecture should implement two main principles:

• Minimize the functionality of client components, leaving only user interface functions to the client;
• Free the database server from functions it should not run.

Such architecture distributes processing modules more efficiently, which in this case are executed on the server (or on several separate servers).

These software modules perform server functions for interacting with users and client functions for database servers. In addition, different application servers can interact with each other to more accurately divide the system into functional blocks that perform specific roles.

Vertical and Horizontal Scaling of Web Services

Vertical scaling implies increasing the performance of each system component to improve the overall performance of web services.

Scalability in web service development in this context means the ability to replace components of an existing computing system with more powerful and faster ones.

This is the simplest approach to scaling web services, as it does not require any changes to the application programs running in such systems.

Horizontal scaling is dividing a system into smaller structural units at the architecture or development stage of a web service. Services are distributed across separate physical devices, and the number of servers simultaneously performing the same function is increased as needed.

In this case, scalability implies the ability to add new nodes and servers to the system to improve overall performance.

This approach to scaling often requires certain changes to the web service during development that will allow full utilization of additional resources.

Scalability Principles in Web Service Development

When creating a scalable web service, the following principles should form its foundation:

• Uninterrupted operation. In addition to availability, the service must have high performance. Otherwise, you risk a negative reaction from customers and lower the site's positions in search results. Google and Yandex index such sites worse. A web service with low performance is unlikely to attract a serious audience.
• Constant availability. It is very important for companies that their web service is available at all times. Every missed minute causes serious damage to the company's profits and reputation. For SaaS and cloud services, it is critical to ensure continuous access to services throughout their entire lifecycle. Therefore, it is necessary that the scalable web service is available at any time of day and from anywhere in the world.
• Fast data search across databases. Working with data usually entails significant performance issues. This is because third-party technologies are typically used for data storage and access, and integrating them is no simple task. Vulnerabilities are often found at the junction of the main application part and database services.
• Fault tracking. The system should be easy to operate, maintain, and update. Additionally, any problems that may arise during the product's operational phase should be easily tracked and fixed. Good results are achieved by properly structuring and segmenting the application into relatively isolated components during development and service architecture planning.
• Real-time response. Of course, the speed of the web application is important. This applies not only to obtaining information about storage or overall performance, but also to the speed of operations and response. No matter how useful the application is, you have only a few seconds to meet the client's needs. If you fail to do so in this time, the client will go to competitors.

Scalable Design Methods and Strategies

The following methods will help in the development and design of a scalable web service:

1. Microservices and node functioning. This refers to a service-oriented architecture (SOA) in which each service has its own functional context and should not affect other services. Each component in web service development has its own function and proper connection to other services. The emphasis is not on speed and ease of development, but on structural integrity, which in the future will save a lot of time and effort spent on maintaining the old design. As a result, problems are isolated. That is, problems with one function will not affect others. The same applies to application nodes.
2. Load balancers. Load balancers are critical for scalable web services because they distribute the load as the number of concurrent connections increases, and also distribute connections across nodes. This allows you to increase the performance of the developed web service by adding nodes. The load balancer distributes loads according to specified criteria. For working with a complex system, it is recommended to use multiple load balancers.

Cache is used at different application levels, the method works after the web service has been developed, and this idea is best implemented in the following:

• You can insert a cache on the requesting node to make data retrieval for your clients nearly instantaneous. The more nodes the application has, the more caches there will be, since each web service node must have its own cache.
• If you need to create a single shared cache for all nodes and thus avoid numerous cache misses, a global cache is used.
• A distributed cache distributes data fragments across all nodes. The more data is cached closer to the user, the faster it is retrieved.
• Proxy. The main advantage of a proxy in scaling is coordinating multiple requests. It can collapse several identical requests into one and reduce the number of requests to the database disk. Thus, response time and database performance increase. The best practice in web service operation is to use proxies – combining them with caches. In this case, their use is considered most beneficial.
• Indexing. Indexes are closely related to data retrieval when data is distributed across physical devices. They allow quickly finding a small piece of information in a huge database, even if it's distributed across many physical devices.

For developing and implementing fast search, index tables are used, depending on where this data is located. Although the query is added to both the search and the table, the user will get a response faster due to indexing.

Despite the obvious advantages of this approach, tables become too cumbersome when data volume increases significantly. Therefore, they must be used with caution.

• Queue. As the development and total number of web services grows, the procedure for writing and processing requests may slow down. There is also a need to regulate simultaneous requests and handle a large number of requests. In this case, it makes sense to execute some requests asynchronously and queue them. This allows the client to make a request, receive confirmation, and then move on to other work, periodically checking on it. In the normal case, the client is forced to wait until the request is processed, without doing any other work.