Friday, May 17, 2013

Ganeti Migration

It is common to want to do a 'Texas two-step' with your ganeti nodes. The idea being that you migrate everything off of a node, reboot it for patches, then migrate everything back, and do this around your cluster until you've patched all your hypervisors. Easier said than done!

The fast way:

# move primaries off node
gnt-node migrate $node

# move secondaries off node
gnt-node evacuate --secondary-only $node
Sometimes nodes fail to migrate. I don't know why. I just use the gnt-instance failover command to move them which requires a reboot. Sometimes the secondary disks don't move either. This is more annoying because hail crashes before making a plan for you. I have written the following script to, stupidly, move all the secondaries off of one node onto other nodes so you can reboot a node in your cluster without fear.

if [ -z $evac_node ]; then
echo "Please specify a node to evac"
exit 1

echo "Evacuating secondaries from $evac_node"

HYPERVISORS=`wget --no-check-certificate -O-  https://localhost:5080/2/nodes 2>/dev/null | grep id | awk '{print $NF}' | tr -d \",`

for instance in `gnt-instance list -o name,snodes  | grep $evac_node | cut -d " " -f 1`
        current_primary=`gnt-instance list -o name,pnode | grep $instance | awk '{print $NF}'`
        target_node=`echo $HYPERVISORS | sed 's/ /\n/g' | grep -v $evac_node | grep -v $current_primary | sort -R | head -n 1`
        echo "gnt-instance replace-disks -n $target_node $instance"
        gnt-instance replace-disks -n $target_node $instance
Happy hacking!

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