Eureka is a REST (Representational State Transfer) based service that is primarily used in the AWS cloud for locating services for the purpose of load balancing and failover of middle-tier servers.
At Netflix, Eureka is used for the following purposes apart from playing a critical part in mid-tier load balancing.
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For aiding Netflix Asgard - an open source service which makes cloud deployments easier, in - Fast rollback of versions in case of problems avoiding the re-launch of 100's of instances which could take a long time.
- In rolling pushes, for avoiding propagation of a new version to all instances in case of problems.
 
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For our cassandra deployments to take instances out of traffic for maintenance. 
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For our memcached caching services to identify the list of nodes in the ring. 
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For carrying other additional application specific metadata about services for various other reasons. 
[Eureka Google Group] (https://groups.google.com/forum/?fromgroups#!forum/eureka_netflix)
Please see [wiki] (https://github.com/Netflix/eureka/wiki) for detailed documentation.