Elastic Load Balancer with Only One EC2 Instance

Mike Rosenberg

Service Category

Networking

Cloud Provider

AWS

Service Name

AWS ELB

Inefficiency Type

Inefficient Architecture

Explanation

An ELB with only one registered EC2 instance does not achieve its core purpose—distributing traffic across multiple backends. In this configuration, the ELB adds complexity and cost without improving availability, scalability, or fault tolerance. This setup is often the result of premature scaling design or misunderstood architecture patterns. If there's no plan to horizontally scale the application, the ELB can often be removed entirely without user impact.

Relevant Billing Model

All ELB types are billed per hour of provisioned uptime and, in most cases, per GB of data processed. These charges apply regardless of the number of targets or the actual volume of traffic being handled. Running an ELB with only a single EC2 instance incurs fixed costs without delivering the intended benefits of load distribution or redundancy.

Detection

Identify load balancers with only one healthy or active EC2 instance registered
Check ELB metadata and target group configurations to validate instance count
Review deployment patterns to determine whether the architecture expects scaling but hasn't implemented it
Assess whether the ELB is used for static routing or simply passing traffic to a single backend

Remediation

If no scaling is planned or needed, remove the ELB and route traffic directly to the EC2 instance using a static IP or DNS entry
If future scaling is expected, consider retaining the ELB but update documentation and monitoring to ensure it doesn't remain in this state long-term
Document architectural decisions around ELB usage to prevent future misconfigurations

Relevant Documentation

Elastic Load Balancing Pricing

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