Let's say I'm using Amazon's EC2 load balancer. I have it hooked up to two instances (excuse me if my terminology isn't correct). What happens if the load balancer fails? Do both instances fail to work now?

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    Stuff explodes.
    – Josh K
    May 6, 2010 at 4:32
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    Dec 2, 2010 at 4:50

2 Answers 2


Typically load balancers are clustered together into a high-availability pair.

If one load balancer fails, the secondary picks up the failure and becomes active. They have a heartbeat link between them that monitors status.

If all load balancers fail (or are accidentally misconfigured), servers down-stream are knocked offline until the problem is resolved, or you manually route around them.

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    +1 I bet in general: Misconfiguration > Hardware + Software Failure May 6, 2010 at 12:19

Yes if the load balancer instances both fail the service is essentially dead. Note that amazons uptime includes up to 4 hours of downtime a year (99.95%)

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