Hacker News Reader

Comment by raxxorraxor | Hacker News Reader

A snapshot of the current data? So the data is still available and another snapshot can be created?

It reads like it indeed does not affect live data in running cloudservers, yes.

Aside from backups, the snapshots can also be used as base images to provision new nodes though, losing those could indeed be inconvenient.

I was always under the impression that a snapshot should be an short-lived thing. E.g. you take a snapshot, make a backup or copy from that, then delete the snapshot. Where I work, the VM admins will only allow one snapshot at any point in time without special request and justification, and they encourage deleting the snapshot within 72 hours.

Depends on the solution, but in many systems snapshots are cheap, like zfs or btrfs. I can imagine ceph snapshots being quite cheap too.

Edit: people use snapshots to compliment backups too, you can do snapshots hourly and back a snapshot up daily. (They don't act as backups, more like "oops" revert solutions, humans are more likely to fail than machines)

If you're using VMware or Hyper-V the backups rely on a dirty "bitmap" of which blocks has been written since last backup so it only has to pull those from the system, this doesn't work with more snapshots for some reason. Enterprise backup solutions will just pull the entire machine and compare what's changed anyways, but you usually get a warning about it. So grumpy admins

Yes it's VMware.

You're using a rather narrow/implementation specific definition of snapshot.

I believe EBS snapshots are equivalent to you temp-snapshot, incremental/deduplicated backup/delete temp snapshot combination. Logically it's still a snapshot, because it contains all data of the volume at a specific point in time, but the cloud provider abstracts away the details of how it achieves durability.

Also old snapshots

Snapshots are often used for deployment of systems. What happens if the snapshot you rely on as a base image gets lost?

Create a new one?

If the base snapshot is gone, all future snapshots that rely on that snapshot may be invalid. Depends on exactly how snapshots are implemented. Are they a delta of the previous snapshot? Are they a full copy of the device?

Hetzner snapshots are fully independent disk images, nothing more, nothing less.

Thanks! $20 seems kinda fair then, I guess.

Base images should be repeatable anyway using packer etc.

Even though this is a bit tricky on the hetzner cloud, because it requires the addition of a static route[1] to access the internet which isn't pushed by the DHCP, and I haven't been able to fully automate that in debians preseed for the life of me.

Yes it's offtopic, but that's one really frustrating thing. Maybe someone here has a solution.

1: https://docs.hetzner.com/cloud/servers/iso-installation-gate...

cloud-init?

cloud-init does help us, once we have a working linux, but we can also bake the static route into a base image.

The problem is that preseed is a very minimal linux environment and either relies on DHCP to work, or to use the usual network config DHCP sets (address, netmask, gateway). Arbitrary routes are not a possibility there. And ways to run abitrary commands to just <ip r> something come after the network initialization, which fails in that setup. The same holds for the kernel network bootstrapping parameters, I haven't found a way to add an arbitrary route there yet.

And for some reason, kickstart is able to handle this with it's centos/RHEL base.

Reply on news.ycombinator.com