Re: [pve-devel] [PATCH container] fix #3424: vzdump: cleanup: wait for active replication

[Thomas Lamprecht <t.lamprecht@proxmox.com>]

On 14.01.22 12:55, Fabian Ebner wrote:
> As replication and backup can happen at the same time, the vzdump
> snapshot might be actively used by replication when backup tries
> to cleanup, resulting in a not (or only partially) removed snapshot
> and locked (snapshot-delete) container.
> 
> Wait up to 10 minutes for any ongoing replication. If replication
> doesn't finish in time, the fact that there is no attempt to remove
> the snapshot means that there's no risk for the container to end up in
> a locked state. And the beginning of the next backup will force remove
> the left-over snapshot, which will very likely succeed even at the
> storage layer, because the replication really should be done by then
> (subsequent replications shouldn't matter as they don't need to
> re-transfer the vzdump snapshot).
> 
> Suggested-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
> Signed-off-by: Fabian Ebner <f.ebner@proxmox.com>
> ---
> 
> VM backups are not affected by this, because they don't use
> storage/config snapshots, but use pve-qemu's block layer.
> 
> Decided to go for this approach rather than replication waiting on
> backup, because "full backup can take much longer than replication
> usually does", and even if we time out, we can just skip the removal
> for now and have the next backup do it.
> 
>  src/PVE/VZDump/LXC.pm | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/src/PVE/VZDump/LXC.pm b/src/PVE/VZDump/LXC.pm
> index b7f7463..10edae9 100644
> --- a/src/PVE/VZDump/LXC.pm
> +++ b/src/PVE/VZDump/LXC.pm
> @@ -8,6 +8,7 @@ use File::Path;
>  use POSIX qw(strftime);
>  
>  use PVE::Cluster qw(cfs_read_file);
> +use PVE::GuestHelpers;
>  use PVE::INotify;
>  use PVE::LXC::Config;
>  use PVE::LXC;
> @@ -476,8 +477,14 @@ sub cleanup {
>      }
>  
>      if ($task->{cleanup}->{remove_snapshot}) {
> -	$self->loginfo("cleanup temporary 'vzdump' snapshot");
> -	PVE::LXC::Config->snapshot_delete($vmid, 'vzdump', 0);
> +	$self->loginfo("checking/waiting for replication..");

do we know if replication is setup at this stage? as I'd like to avoid
logging that if that's not the case to avoid user confusion.

> +	eval {
> +	    PVE::GuestHelpers::guest_migration_lock($vmid, 600, sub {
> +		$self->loginfo("cleanup temporary 'vzdump' snapshot");
> +		PVE::LXC::Config->snapshot_delete($vmid, 'vzdump', 0);
> +	    });
> +	};
> +	die "snapshot 'vzdump' was not (fully) removed - $@" if $@;
>      }
>  }
>