Short question:
How do I know if an instance has ephemeral storage attached? Do I have to ssh in and look at the mounts with lsblk on Linux?
Since ephemeral storage is lost when an instance is stopped, you need to know if ephemeral drives are attached at all. The first thing to check is the “root device type” of the instance, if it is EBS, then you don’t have to worry about losing data (unless the EBS volume is set to ‘delete on terminate’).
However, if it is “instance-store” you will lose the data on that drive when the instance starts. Then look at the “root device” and “block devices” and see if they are all associated with EBS volumes. That’s easy. Where it gets cloudy, is when you attach an ephemeral drive to an instance (at launch time), but the console doesn’t represent it like it does for an additional EBS volume. Further, you may need to manually mount the drive yourself…
How can you easily know from the AWS Console if an ephemeral drive is attached?
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Answer
Not the answer you want to hear but you cannot tell this from the console. As you noted there are 2 things that need to happen for data to be written to an ephemeral drive
1) You need to actually have that dev mounted. No way of telling from the console on this for any dev 2) You need to have that dev exposed to the instance via block mapping in the AMI.
You can assume that most (but not all) public AMIs will have all the possible ephemeral drives mapped (although hi1.8xl has 24 of these drives) and so then you just need to check if the instance type actually has support for ephemeral drives as many don’t.
If you wish to avoid ephemeral drives being used, you should limit deployments to AMIs that you have created and removed any ephemeral drives from the block device mappings.