[pve-devel] [PATCH manager] api2 tools: rrd data: prefer new-format keys over old-format keys

[Friedrich Weber <f.weber@proxmox.com>]

This fixes an issue where on a fresh Proxmox VE 9 cluster, the status
of the first VM/container would not be updated in the resource tree
for the first 5 minutes after creation. For example, starting the
newly created guest after the first pvestatd status update would not
update the state to "running" for 5 minutes.

The reason is that pvestatd, when broadcasting RRD data, checks for
existence of /var/lib/rrdcached/db/pve-vm-9.0/ to decide whether to
send RRD data with new-format (pve-vm-9.0/) or old-format (pve2.3-vm/)
keys. The directory does not exist on nodes of a fresh cluster without
guests, so pvestatd falls back to sending an old-format key. pmxcfs,
upon receiving the key, creates the directory, so on the next pvestatd
status update, pvestatd will send out new-format keys. But until the
entry with the old-format key expires (after 5 minutes), both the
new-format and the old-format key exist in the RRD data. Currently, if
both keys are present, get_rrd_key will return the old-format key,
meaning that any status updates with the new-format key are not
registered. In order to fix this, prefer the new-format key if it is
present.

Signed-off-by: Friedrich Weber <f.weber@proxmox.com>
---

Notes:
    Encountered during a training, where one is more likely to closely
    watch the state of the first created guest.
    
    I'm unsure if this is a good fix.
    
    An alternative fix for this particular case would be to instead have
    pvestatd always send out new-style keys on a fresh cluster.
    
    However, another situation where there could be both old-format and
    new-format keys is in a mixed 8+9 cluster (e.g. during upgrade).
    
    One issue is that get_rrd_key on 8 would still prefer old-style keys
    (unless we backport this patch to 8), so behavior on 8 and 9 would be
    different.
    
    Another issue is that having both an old-format and new-format key
    could happen after migrating a VM from a PVE 8 node (sending
    old-format keys) to a PVE 9 node (sending new-format keys). In this
    direction, I guess we also want to prefer new-format keys over the
    old-format keys. But when migrating a VM from a PVE 9 (sending
    new-format keys) to a PVE 8 node (sending old-format keys) -- which is
    admittedly not supported -- it would make more sense to prefer
    old-format keys.
    
    Perhaps a better solution is, if both old-format and new-format keys
    are present, to prefer the key whose entry has the more recent
    timestamp (ctime)?

 PVE/API2Tools.pm | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/PVE/API2Tools.pm b/PVE/API2Tools.pm
index 863f5f55..a1a6f39e 100644
--- a/PVE/API2Tools.pm
+++ b/PVE/API2Tools.pm
@@ -45,17 +45,17 @@ sub get_hwaddress {
 sub get_rrd_key {
     my ($rrd, $type, $id) = @_;
 
+    my $key = "pve-${type}-9.0/${id}";
+    if (defined($rrd->{$key})) {
+        return $key;
+    }
+
     # check for old formats: pve2-{type}/{id}. For VMs and CTs the version number is different than for nodes and storages
     if ($type ne "vm" && exists $rrd->{"pve2-${type}/${id}"}) {
         return "pve2-${type}/${id}";
     } elsif ($type eq "vm" && exists $rrd->{"pve2.3-${type}/${id}"}) {
         return "pve2.3-${type}/${id}";
     }
-
-    my $key = "pve-${type}-9.0/${id}";
-    if (defined($rrd->{$key})) {
-        return $key;
-    }
 }
 
 sub extract_node_stats {
-- 
2.47.2



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