Pre-Freeze-/Post-Thaw-Script with xe-guest-utilities

KPS

Hi!

As quiesced snapshots are deprecated and RAM-enabled backups require some downtime:

What do you think about the concept of "Pre-Freeze"-scripts through xe-guest-utilities? Would it be possible to have some scripts on the snapshotted system, that are getting executed, when a snapshot is taken?

Example for VMWare:
https://www.veritas.com/support/en_US/article.100009553

Best wishes
KPS

olivierlambert

Hi,

If you have PV drivers installed in your guests, a snapshot should be coherent anyway (I can at least tell you that's the case on Linux)
There's already a feature we started in XO, see https://xen-orchestra.com/blog/xen-orchestra-5-75/#-webhooks-for-snapshots-beta for use of webhooks

KPS

@olivierlambert
Thank your for your answer.

About the options:

Coherent snapshot: With a pre-freeze-script, it would be 100% possible to bring every system in a consistent state.
Webhooks: Can do the same, but are a lot more work than a local script. Especially for windows VMs, I would have to install a webserver, that can trigger scripts.

olivierlambert

That's why we planned to improve the tools (at least on Linux at first) to allow more things to be passed directly to it

KPS

@olivierlambert
Sounds great. I would be very happy to see this on Linux and Windows.
Thank you for your effort!

olivierlambert

It's a big effort indeed, this is costing a lot of money

rjt

@olivierlambert awesome!

I assume Windows VMs that get their drivers from Windows Update will not have this capability unless we install the simple service:1727.

On github, it says that the the VM service has to respond within 1 minute, but it would take several minutes to backup a database. The blog page says it will wait for answer. Sounds like Vates knows the answer is somewhere in between. We will wait, but only for so long

Specification

XO will waits for the request to be answered before starting the snapshot, but will not wait longer than 1 minute.

If the request fails for any reason, XO will go ahead with snapshot immediately.

Webhooks for snapshots [beta] says "It's now possible to notify a VM via an HTTP request before a snapshot. Xen Orchestra will wait for an answer before starting the actual snapshot."

olivierlambert

@julien-f can answer that question

julien-f

@rjt You can customize the hook timeout by adding this setting in your xo-server's config:

[xapiOptions]
# Timeout in milliseconds
syncHookTimeout = 300e3 # 5 minutes