Synchronous decoupling

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

Synchronous decoupling separates request handling components while requiring the caller to wait for a response through an intermediary such as a load balancer.

Synchronous decoupling separates request-handling components while keeping the caller waiting for a response. A load balancer lets clients reach backend instances without knowing which instance serves each request. section 14.0 section 14.3

A load balancer provides the central implementation pattern:

• Receives requests and distributes them across backend instances. section 14.0
• Checks backend health periodically and stops routing traffic to failed instances. section 14.3 section 16.1.2
• Works with Auto Scaling across availability zones so replacement instances can receive traffic after failures. section 16.1.2 section 17.4

Fault-tolerant web application

Place an Elastic Load Balancer in front of EC2 instances distributed across multiple subnets and availability zones. If one instance fails, health checks remove it from rotation while an Auto Scaling group replaces it. Unlike asynchronous decoupling with SQS, the request still requires an available backend response. section 16.1.2 section 14.3

Figure 16.3 Fault-tolerant EC2 instances with an Auto Scaling group and an Elastic Load Balancer

Shows how an Auto Scaling group and Elastic Load Balancer provide redundant, synchronously decoupled EC2 instances. section 16.1.2

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

How deep it goes

Explains load-balancer routing, health checks, redundancy, and Auto Scaling, but stops short of implementation commands or configuration.

Examples

Uses a video-chat analogy and a redundant EC2 web application behind an Elastic Load Balancer.

What it assumes

Assumes understanding of autoscaling and distinguishes synchronous communication from asynchronous queue-based processing.

What you can do after

Evaluate how a load balancer can distribute traffic and remove failed instances in a redundant EC2 architecture.

How it connects

Connects load balancing with Elastic Load Balancing, Auto Scaling, EC2, availability zones, health checks, and asynchronous decoupling.

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Related concepts

• AWS Elastic Load Balancingimplemented by · AWS Elastic Load Balancing is a managed service that distributes incoming application traffic across multiple targets and can route traffic away from unhealthy targets.
• load balancinguses · 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 callcontrasts with · A synchronous call is an invocation in which the caller waits for the operation to complete or return a response before continuing.

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.