S3 uses a set of front-end servers to provide access to the underlying data. The decision about which front-end server to use is handled via load-balancing DNS service. When the IP address of an S3 bucket is looked up, the choice of which IP address to return to the client is made based on the current load of the front-end servers.

Over time, the load across the front-end changes, so those servers that are considered "lightly loaded" change. This means that if the DNS value is cached for any length of time, applications may end up talking to an overloaded server; or, in the case of failures, they may end up trying to talk to a server that is no longer there.

And, for historical security reasons, in the era of applets, the DNS TTL of a JVM is set to "infinity" by default.

To improve AWS load-balancing, set the DNS time-to-live of an application which works with Amazon S3 to something lower than the default. Refer to Setting the JVM TTL for DNS Name Lookups in the AWS documentation.