What is Elastic Load Balancing?
Elastic Load Balancing is a part of Amazon Web Services (AWS) that improves the availability and fault tolerance of your applications. It achieves this by distributing the incoming network traffic across multiple targets to optimize resource use, avoid overload, and ensure no single point of failure.
ELB can handle varying levels of traffic in applications and route traffic intelligently based on the request's parameters.
The main purpose of ELB is to provide:
- High availability: Ensures your application is deployed across multiple Availability Zones to tolerate failures and maintain uptime.
- Automatic scaling: Scales the application automatically according to the incoming traffic load.
- Health checks: Continuously monitors the health of the targets to distribute traffic to only healthy instances.
- Security: Provides robust security features, including integrated certificate management and SSL/TLS encryption.
Types of Elastic Load Balancers
There are three primary types of elastic load balancers provided by AWS, each designed to handle different use cases and provide unique features:
Application Load Balancer (ALB)
Application Load Balancer is best suited for HTTP and HTTPS traffic. It operates at the application layer (Layer 7) of the OSI model, making it ideal for content-based routing and HTTP header inspection. ALB allows you to direct traffic based on the contents of the request, such as routing requests to different target groups based on URL paths or query strings.
Notable features include:
- Host-based or path-based routing
- Support for WebSockets
- Content-based routing decisions
- SSL termination and web application firewall (WAF) integration
Network Load Balancer (NLB)
Network Load Balancer is designed for extreme performance and operates at the transport layer (Layer 4) of the OSI model. It handles millions of requests per second while maintaining ultra-low latencies. NLB is best suited for TCP, UDP, and TLS traffic when fast and high-capacity load balancing is necessary.
Notable features include:
- Static IP addresses for the load balancer
- Support for volatile workloads that can change quickly
- Direct connection with the TCP/UDP protocols
- Elastic IP integration
Gateway Load Balancer (GLB)
Gateway Load Balancer allows you to deploy, scale, and manage your own virtual appliances, such as firewalls, intrusion detection and prevention systems, deep packet inspection systems, and others. It operates at the network layer (Layer 3) and distributes traffic efficiently across multiple virtual appliances.
Notable features include:
- Simplified integration of third-party networking and security appliances
- Load balancing across multiple virtual appliance instances
- Built-in fault tolerance and high availability
- Advanced traffic steering capabilities
How ELB Works
To understand how ELB works, consider the following key components:
Targets
Targets are endpoints that receive traffic distributed by the load balancer. These targets can be EC2 instances, IP addresses, Lambda functions, or containers. Each target must be registered with the load balancer in a specific target group.
Target Groups
Target groups are sets of targets organized based on application needs. You define health check parameters to monitor the status of targets within the target group. The load balancer routes requests to the targets in a particular target group as configured in your routing rules.
Listeners
Listeners process inbound connections from clients based on configured rules. Each listener defines a protocol and port for front-end connections, and rules determine how requests are routed to the target groups on the back end.
Health Checks
Health checks are configurations that help ensure that traffic is only sent to healthy instances. The load balancer periodically sends requests to check the health of each registered target. If a target fails these health checks, it is automatically removed from the routing pool until it recovers.
Benefits of Elastic Load Balancing
ELB offers several significant benefits for ensuring your application's resiliency, performance, and security:
- Fault Tolerance: By distributing traffic across multiple targets in different Availability Zones, ELB enhances fault tolerance. If one target becomes unavailable, traffic can be redirected to other healthy targets.
- Auto Scaling: ELB works seamlessly with AWS Auto Scaling to automatically adjust capacity based on traffic demands, ensuring consistent application performance.
- Improved Security: ELB supports the use of Secure Sockets Layer (SSL) certificates for traffic encryption, thus providing a secure layer for traffic in transit. It also integrates with AWS Identity and Access Management (IAM) to allow fine-grained access control.
- Ease of Integration: ELB integrates with various AWS services like Amazon CloudWatch for monitoring, AWS CloudFormation for infrastructure as code, and Elastic Beanstalk for deployment and management of applications.
Best Practices for Using ELB
To get the most out of ELB, consider implementing the following best practices:
- Enable Cross-Zone Load Balancing: This ensures that traffic is evenly distributed across all your targets, irrespective of their Availability Zones, preventing one zone from getting overloaded.
- Regularly Monitor your Load Balancers: Utilize Amazon CloudWatch metrics to continuously monitor your load balancer's status and performance. Set alarms to get notified when issues arise.
- Use Weighted Target Groups: When you have multiple target groups, you can control the distribution of traffic between them by assigning weights, making gradual traffic shifts easier.
- SSL Termination: Terminate SSL connections at the load balancer instead of individual instances to simplify certificate management and reduce the processing burden on your instances.
- Optimize Application Health Monitoring: Customize health check parameters to match your application’s specific health indicators accurately. Proper health check configurations ensure traffic is only sent to healthy instances.
Conclusion
To sum up, Elastic Load Balancing (ELB) is an essential AWS service that provides built-in high availability, automatic scaling, robust security, and efficient traffic distribution, ensuring that your applications perform reliably under varying traffic loads. With its three types—Application Load Balancer, Network Load Balancer, and Gateway Load Balancer—AWS ELB caters to diverse use cases and offers significant enhancements to the resilience, performance, and security of your applications.