Configure an AWS ELB in your deployment architecture even if you are using a single EC2 instance behind it. This will ensure you are ready to scale up or down without interrupting your services. ELB ensures the CNAME application access point remains the same, as you auto scale the number of servers or even replace a fleet of servers behind it. This can also help you systematically roll out new versions of your application behind the ELB without service interruptions for your customers.
ELBs work within an AWS region only, however, they can work across multiple AZs within a region. Typically, for very large installations where you might want to distribute traffic across multiple AWS regions, ...
