AWS Elastic Load Balancing

As explained in Amazon Web Services in Action, Third Edition: An in-depth guide to AWS

Elastic Load Balancing is an AWS managed service that distributes incoming traffic across multiple targets and can remove unhealthy targets from service.

AWS Elastic Load Balancing (ELB) provides managed load balancers that sit between clients and application targets. A browser sends its request to the load balancer, which forwards it to a target and returns the response. Clients need to know the load balancer, not the individual web servers. This is synchronous decoupling: the client still waits for an immediate response. section 14.0 section 14.1

Choose a load balancer type for the traffic it must handle:

• Application Load Balancer (ALB) supports HTTP and HTTPS. Use it when those protocols are all the application needs. section 14.1
• Network Load Balancer (NLB) supports TCP and TCP TLS. Use it when an ALB does not fit the protocol. section 14.1
• Classic Load Balancer (CLB) supports HTTP, HTTPS, TCP, and TCP TLS, but is treated as deprecated. section 14.1

Two-server WordPress deployment

Put an ALB in front of two EC2 virtual machines running WordPress. Expose the load balancer rather than the web servers to clients; a security group can allow internet HTTP traffic to port 80 of the load balancer. Health checks determine whether a machine receives requests. If one fails, the load balancer stops sending it traffic, and the other must handle requests until the failed machine is replaced. The servers can share application files through EFS and use RDS for MySQL. section 2.1 section 14.1

Figure 2.1 The company’s blogging infrastructure consists of two load-balanced web servers running WordPress, a network filesystem, and a MySQL database server.

The diagram places the load balancer ahead of two WordPress servers and shows their shared filesystem and database. section 2.1

ELB load balancers are fault tolerant and scalable, but a load balancer cannot make a single EC2 instance fault tolerant. Use redundant instances; Auto Scaling groups can maintain a fleet. Health checks keep an unready backend out of service, but surviving targets still need enough capacity. Manage load balancers in the EC2 Management Console. Unlike SQS, ELB does not make a request asynchronous: the target must be available to answer it. section 14.1 section 16.0 section 14.3

How Amazon Web Services in Action, Third Edition: An in-depth guide to AWS covers it

How deep it goes

Explains request forwarding, health checks, protocol-based selection, and architectural placement; does not detail a load balancer configuration procedure.

Examples

Uses a two-server WordPress deployment with an ALB, health checks, shared EFS files, and an RDS MySQL database.

What it assumes

Introduces the request path through a browser, load balancer, and EC2 instance without assuming load balancer configuration knowledge.

What you can do after

Evaluate/understand how to choose ALB or NLB, place it ahead of redundant targets, and account for failed-target capacity.

How it connects

Connects ELB to EC2, Auto Scaling groups, security groups, and synchronous decoupling, while contrasting it with SQS-based asynchronous decoupling.

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Related concepts

• load balancingimplements · Load balancing is the distribution of requests or computational work across multiple resources to manage demand, reduce workload imbalance, and improve utilization or availability.
• synchronous decouplingimplements · Synchronous decoupling separates request handling components while requiring the caller to wait for a response through an intermediary such as a load balancer.
• AWS consolepart of · The AWS console is a web-based graphical interface for configuring, operating, and managing Amazon Web Services resources and services.
• load balancerkind of · A load balancer is a hardware or software component that distributes incoming network traffic or requests among multiple destinations, such as servers or service instances.
• Azure Load Balanceralternative to · Azure Load Balancer is a managed Azure service that distributes network traffic across backend resources according to configured rules and health status.

This explainer was generated by Manning's knowledge graph from the text of Amazon Web Services in Action, Third Edition: An in-depth guide to AWS. The section links point to the parts of the book it draws on.