The "ephemeral" term is a legacy. Unfortunately it is part of the EC2 API for the block device mapping [1] of the "classic" instance store interfaces on the Xen platform. I don't know exactly when we stopped using "ephemeral" in our documentation, but I think it was with the introduction of EBS around 2008.
The "ephemeral" term confuses a lot of customers, and that's why we stopped using it. Data written to local storage is not transient, fleeting, or short lived. By 2010 we had transitioned to using "instance storage" in the documentation [2], which included a big note about how the data remains if an instance reboots for any reason (planned or unplanned).
Still, there is a misconception that data on local instance store volumes (both the more "classic" HDD or SSD volumes that are virtualized by Xen, as well as the new generation of local NVMe storage) could vanish due to this vestigial term that lingers in the API. Many customers, as well as services like Amazon Aurora [3], build highly durable and available systems on local instance storage.
The "ephemeral" term is a legacy. Unfortunately it is part of the EC2 API for the block device mapping [1] of the "classic" instance store interfaces on the Xen platform. I don't know exactly when we stopped using "ephemeral" in our documentation, but I think it was with the introduction of EBS around 2008.
The "ephemeral" term confuses a lot of customers, and that's why we stopped using it. Data written to local storage is not transient, fleeting, or short lived. By 2010 we had transitioned to using "instance storage" in the documentation [2], which included a big note about how the data remains if an instance reboots for any reason (planned or unplanned).
Still, there is a misconception that data on local instance store volumes (both the more "classic" HDD or SSD volumes that are virtualized by Xen, as well as the new generation of local NVMe storage) could vanish due to this vestigial term that lingers in the API. Many customers, as well as services like Amazon Aurora [3], build highly durable and available systems on local instance storage.
[1] https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/block-de...
[2] https://web.archive.org/web/20111113011016fw_/http://docs.am...
[3] https://www.allthingsdistributed.com/files/p1041-verbitski.p...