Guides

What is Load Balancing?

Developer Relations Team on Oct 9, 2023

What is load balancing?

Load balancing is used in computer networking and distributed systems to evenly distribute incoming network traffic or workloads across multiple backend servers, ensuring optimal performance and resource utilization. It is particularly important in real-time chat and messaging applications that require high availability and responsiveness.

When a server becomes overloaded due to increased traffic or workload, it can slow down or even crash, leading to a poor user experience. Load balancing addresses this issue by distributing the traffic across multiple servers, preventing any single server from being overwhelmed.

How does load balancing work?

Load balancing is crucial in ensuring the scalability and availability of applications and services. The basic principle behind load balancing is evenly distributing incoming traffic across multiple servers. This is done through a load balancer, which acts as a reverse proxy between clients and servers. When a client sends a request, it is intercepted by the load balancer, which then determines the most suitable server to handle the request.

There are several techniques and algorithms used to achieve load balancing at different levels of the network stack, including:

DNS-level load balancing: This involves distributing traffic across multiple IP addresses associated with a domain name. DNS servers can provide different IP addresses in response to DNS queries, effectively distributing traffic among multiple servers.
Network-level load balancing: This uses network devices, such as routers or switches, that distribute traffic based on network-layer information, such as IP addresses or TCP/UDP ports. Network load balancers can provide scalability and redundancy by distributing traffic across multiple server clusters.
Application-level load balancing: This is typically done by software load balancers or application delivery controllers (ADCs) that operate at the application layer. These devices can inspect application-layer protocols like HTTP and make load-balancing decisions based on application-specific criteria, such as session information or content.

What are the different types of load balancing?

Various load-balancing techniques can distribute incoming network traffic across multiple servers or resources. Here are some of the common types:

Round Robin: In this method, incoming requests are distributed equally among the available servers in a cyclic manner. Each server in the pool gets an equal share of the load, ensuring fair distribution.

Weighted Round Robin: This approach assigns different weights to each server based on their capabilities and resources. Servers with higher weights receive more incoming traffic, allowing for better utilization of more powerful servers.

Least Connection: This method sends new requests to the server with the fewest active connections. This ensures that the load is balanced based on the current workload of the servers, preventing any single server from being overwhelmed.

IP Hash: In IP hash load balancing, the source IP address of the incoming request is used to determine which server should handle the connection. This technique ensures that requests from the same IP address are consistently directed to the same server, which can benefit session persistence.

Least Response Time: This approach considers the current response time of each server and directs the incoming requests to the server with the lowest response time. It helps distribute the load evenly, ensuring requests are processed quickly and efficiently.

Global Server: Global server load balancing distributes incoming network traffic across multiple servers or data centers located in different geographic locations. It ensures that the traffic is directed to the most optimal server or data center based on availability, performance, and proximity to the end user.

Layer 4: Layer 4 load balancers operate at the transport layer (TCP/UDP) and distribute traffic based on IP address and port number. They can perform load balancing based on factors such as source IP address, destination IP address, source port, and destination port. This allows for efficient distribution of network traffic across multiple servers.

Layer 7: Layer 7 load balancers operate at the application layer and can make load-balancing decisions based on application-specific data, such as HTTP headers, cookies, or session information. This enables more advanced load-balancing strategies, such as session affinity or content-based routing, which can improve performance and user experience.

Content-based: Content-based load balancing involves examining the content of incoming requests and distributing them to servers based on specific content criteria. For example, requests for static content could be directed to servers optimized for delivering static files. In contrast, requests for dynamic content could be sent to servers optimized for processing application logic. This approach can help optimize the use of server resources and improve overall application performance.

Cloud: Cloud load balancing is a technique that distributes network traffic across multiple servers or resources in a cloud computing environment. It optimizes performance, increases availability, and ensures scalability using a load balancer as a backend traffic manager. Cloud load balancing can be achieved at different levels of the network stack, including DNS-level, network-level, and application-level load balancing. This technique is essential for high availability and can protect applications against security threats such as DDoS attacks and web application vulnerabilities.

Hardware: Hardware load balancers are physical devices that distribute network traffic across multiple servers or data centers. They act as intermediaries between the clients and the servers, receiving incoming requests and forwarding them to the appropriate server based on predefined algorithms. Hardware load balancers typically consist of high-performance processors, memory, and specialized software that enable them to handle and distribute traffic efficiently.

Virtual: Virtual load balancers distribute network traffic across multiple servers or data centers like hardware load balancers. They act as intermediaries between the clients and the servers, receiving incoming requests and forwarding them to the appropriate server based on predefined algorithms. The main advantage of virtual load balancers is their flexibility and scalability. Since they are software-based, they can be easily deployed, configured, and managed in virtualized environments or cloud platforms like Google Cloud.

Intelligent Traffic Routing: Intelligent traffic routing uses machine learning and artificial intelligence algorithms to dynamically adapt load-balancing strategies based on real-time data and traffic patterns. This can help optimize resource allocation, improve scalability, and ensure high availability of applications.

These are just some of the common types of load-balancing techniques. The choice of load balancing method depends on factors such as the specific application requirements, the types of traffic being handled, and the desired level of scalability and availability.

Application Load Balancer vs. Classic Load Balancer

When choosing a load balancer for your real-time chat and messaging application, you may come across two popular options: the Application Load Balancer (ALB) and the Classic Load Balancer. Both options have their advantages and considerations, so it's important to understand the differences between them before making a decision.

The ALB operates at the application layer and is designed to handle modern applications with dynamic traffic patterns. It offers advanced features and functionalities that make it well-suited for real-time chat and messaging applications.

On the other hand, the Classic Load Balancer operates at the transport layer and is a more traditional option. It is a proven solution that has been used for years but may not have the same flexibility and scalability as the ALB.

Here are some key differences between the two:

Layer of Operation: The ALB operates at the application layer, inspecting application-layer protocols and making load-balancing decisions based on application-specific criteria. The Classic Load Balancer operates at the transport layer, focusing on distributing traffic based on network-level protocols like TCP and UDP.
Advanced Features: The ALB offers advanced features like SSL termination, content-based routing, and support for WebSockets. These features are particularly useful for real-time chat and messaging applications, as they allow for secure connections and efficient handling of dynamic traffic. The Classic Load Balancer may not have these advanced features.
Cost: There are several factors to consider when considering the cost implications of using the Application Load Balancer (ALB) versus the Classic Load Balancer for real-time chat and messaging applications.
- Pricing Structure: The ALB pricing is based on the number of load balancer hours and the number of data processed through the load balancer. This means you are billed based on the traffic your application receives. On the other hand, the Classic Load Balancer pricing is based on the number of instances running behind the load balancer. This means you are billed based on the number of deployed instances.
- Traffic Patterns: Real-time chat and messaging applications typically have dynamic traffic patterns with frequent spikes in usage. The ALB's pricing structure can be advantageous in this scenario based on the amount of data processed. It allows you to scale up or down based on the demand and only pay for the actual traffic your application receives. In contrast, based on the number of instances, the Classic Load Balancer's pricing may not be as flexible or cost-effective for applications with unpredictable traffic patterns.
- Advanced Features: As mentioned earlier, the ALB offers advanced features like SSL termination, content-based routing, and support for WebSockets, which are particularly useful for real-time chat and messaging applications. While these features contribute to your application's overall functionality and performance, they can also affect the cost. It's important to consider if these features are necessary for your specific application and if the potential benefits outweigh the additional cost.
Scalability: Scalability is crucial for real-time chat and messaging applications, as they must handle varying traffic levels and increased load during peak times. The ALB is designed to handle high-traffic loads and can automatically scale up or down based on demand. This scalability allows you to efficiently handle dynamic traffic patterns without any downtime or performance issues. In comparison, the Classic Load Balancer may not be as efficient in scaling and handling sudden spikes in traffic, which can impact your application's performance and user experience.
Security: Security is critical in real-time chat and messaging applications, as they often involve sensitive user information and require secure connections. The ALB provides enhanced security features such as SSL termination, which allows you to offload the SSL/TLS encryption and decryption process to the load balancer, reducing the computational burden on your application servers. Additionally, the ALB supports AWS Web Application Firewall (WAF) integration, providing an added protection layer against common web exploits and attacks. While the Classic Load Balancer offers some security features, it may not have the same advanced security capabilities as the ALB.

What are the benefits of load balancing?

Load balancing offers several advantages for developers building real-time chat and messaging applications:

Scalability: Load balancing distributes incoming network traffic across multiple servers, enabling applications to handle more concurrent users. This helps prevent bottlenecks and ensures that the application can scale up as the user base grows, leading to improved performance and responsiveness.
High availability: By distributing traffic across multiple servers, load balancing helps ensure that requests can be automatically redirected to other available servers if one server fails or becomes overwhelmed. This improves application availability and minimizes downtime, providing a seamless user experience.
Improved performance: Load balancing can optimize resource utilization by evenly distributing server requests. This prevents any single server from becoming overloaded, which can degrade application performance. Users experience faster response times and reduced latency, leading to an overall improved user experience.
Flexibility: Load balancers can be configured to support different load balancing algorithms, such as round-robin, least connections, or IP hash. This allows developers to fine-tune the load-balancing strategy based on their application requirements, ensuring optimal performance and resource utilization.
Scalability across multiple locations: Load balancing can distribute traffic across multiple data centers or geographic regions, enabling applications to scale horizontally and handle global user traffic. This improves the application's ability to serve users in different locations and provides redundancy in case of data center failures.
Security: Load balancers can act as a single entry point for incoming traffic, providing an additional layer of security by filtering and monitoring incoming requests. They can perform tasks such as SSL termination, which decrypts and encrypts incoming and outgoing traffic. They can also help mitigate distributed denial of service (DDoS) attacks by distributing traffic across multiple servers. Additionally, load balancers can integrate with other security mechanisms, such as web application firewalls (WAFs), to further protect against common web application vulnerabilities.

What are the challenges associated with load balancing?

Load balancing is critical to building scalable and high-performing applications. However, it also comes with its challenges. Here are some of the common ones:

Distribution of traffic: Load balancing efficiently distributes incoming network traffic across multiple servers or resources. The challenge lies in ensuring an equal distribution of traffic without overwhelming any particular server. Some servers may experience a higher load if poorly balanced, leading to performance degradation or system failures.
Dynamic load fluctuations: Real-time applications often experience unpredictable spikes in traffic, making load balancing a constantly changing task. The challenge is quickly adapting to these fluctuations and effectively distributing the load in real time. Failure to handle sudden traffic surges or drops can result in degraded user experience or service outages.
Scalability and growth: As applications grow and user bases expand, load balancing should accommodate increasing traffic and workload. The challenge is to scale the load balancer and the underlying infrastructure without introducing bottlenecks or single points of failure. Ensuring seamless scalability while maintaining optimal performance can be a complex and ongoing challenge.
Session persistence: Some applications require maintaining user sessions or sticky sessions, where subsequent requests from a user should be routed to the same server to maintain the session state. The challenge is balancing the load while ensuring session persistence for a seamless user experience. This can involve additional complexities and overhead in managing and synchronizing session data across multiple servers.
Health monitoring and failover: Load balancers must constantly monitor the health and availability of servers or resources. The load balancer should automatically redirect traffic to healthy servers if a server becomes unresponsive or fails. The challenge is accurately detecting and handling server failures promptly to minimize service disruptions. Effective health monitoring and failover mechanisms can be crucial for high availability.
Security considerations: Load balancers protect applications against various security threats, such as DDoS attacks and web application vulnerabilities. However, load balancing can introduce potential security risks if not properly configured and managed. The challenge is ensuring that load balancers are integrated with other security mechanisms, such as web application firewalls (WAFs), and configured to follow best practices.

Load-Balancing and PubNub

Load balancing is one small part of designing, deploying, and orchestrating a scalable real-time infrastructure. If you’re thinking of building and maintaining your backend infrastructure with open-source technologies and resources, you have to ensure that all the technologies you employ work together to help you build a high-performing, user-friendly app.

Partnering with a third party like PubNub frees you up to focus on the parts of app development you love. With over 15 points of presence worldwide supporting 800 million monthly active users and 99.999% reliability, you’ll never have to worry about outages, concurrency limits, or any latency issues caused by traffic spikes. PubNub is perfect for any application that requires real-time data streaming.