Happy to help you understand, just keep asking questions. :)
The point can be explained this way;
* If two nodes can work without coordination, you don't need a cluster,
just run your services everywhere. If that is not the case, then you
require coordination. Fencing ensures that a node that has entered an
unknown state can be forced into a known state (off). In this way, no
action will be taken by a node unless the peer can be informed, or the
peer is gone.
The method that a node is forced into a known state depends on the
hardware (or infrastructure) you have in your particular setup. So
perhaps, explain what you're nodes are built on and we can assist with
more specific details.
digimer
On 2019-04-17 5:46 p.m., JCA wrote:
Thanks. This implies that I officially do not understand what it is
that fencing can do for me, in my simple cluster. Back to the drawing
board.
On Wed, Apr 17, 2019 at 3:33 PM digimer <li...@alteeve.ca
<mailto:li...@alteeve.ca>> wrote:
Fencing requires some mechanism, outside the nodes themselves,
that can terminate the nodes. Typically, IPMI (iLO, iRMC, RSA,
DRAC, etc) is used for this. Alternatively, switched PDUs are
common. If you don't have these but do have a watchdog timer on
your nodes, SBD (storage-based death) can work.
You can use 'fence_<device> <options> -o status' at the command
line to figure out the what will work with your hardware. Once you
can called 'fence_foo ... -o status' and get the status of each
node, then translating that into a pacemaker configuration is
pretty simple. That's when you enable stonith.
Once stonith is setup and working in pacemaker (ie: you can crash
a node and the peer reboots it), then you will go to DRBD and set
'fencing: resource-and-stonith;' (tells DRBD to block on
communication failure with the peer and request a fence), and then
setup the 'fence-handler /path/to/crm-fence-peer.sh' and
'unfence-handler /path/to/crm-unfence-handler.sh' (I am going from
memory, check the man page to verify syntax).
With all this done; if either pacemaker/corosync or DRBD lose
contact with the peer, they will block and fence. Only after the
peer has been confirmed terminated will IO resume. This way,
split-nodes become effectively impossible.
digimer
On 2019-04-17 5:17 p.m., JCA wrote:
Here is what I did:
# pcs stonith create disk_fencing fence_scsi pcmk_host_list="one
two" pcmk_monitor_action="metadata" pcmk_reboot_action="off"
devices="/dev/disk/by-id/ata-VBOX_HARDDISK_VBaaa429e4-514e8ecb"
meta provides="unfencing"
where ata-VBOX-... corresponds to the device where I have the
partition that is shared between both nodes in my cluster. The
command completes without any errors (that I can see) and after
that I have
# pcs status
Cluster name: ClusterOne
Stack: corosync
Current DC: one (version 1.1.19-8.el7_6.4-c3c624ea3d) - partition
with quorum
Last updated: Wed Apr 17 14:35:25 2019
Last change: Wed Apr 17 14:11:14 2019 by root via cibadmin on one
2 nodes configured
5 resources configured
Online: [ one two ]
Full list of resources:
MyCluster(ocf::myapp:myapp-script):Stopped
Master/Slave Set: DrbdDataClone [DrbdData]
Stopped: [ one two ]
DrbdFS(ocf::heartbeat:Filesystem):Stopped
disk_fencing (stonith:fence_scsi):Stopped
Daemon Status:
corosync: active/enabled
pacemaker: active/enabled
pcsd: active/enabled
Things stay that way indefinitely, until I set stonith-enabled to
false - at which point all the resources above get started
immediately.
Obviously, I am missing something big here. But, what is it?
On Wed, Apr 17, 2019 at 2:59 PM Adam Budziński
<budzinski.a...@gmail.com <mailto:budzinski.a...@gmail.com>> wrote:
You did not configure any fencing device.
śr., 17.04.2019, 22:51 użytkownik JCA <1.41...@gmail.com
<mailto:1.41...@gmail.com>> napisał:
I am trying to get fencing working, as described in the
"Cluster from Scratch" guide, and I am stymied at get-go :-(
The document mentions a property named stonith-enabled.
When I was trying to get my first cluster going, I
noticed that my resources would start only when this
property is set to false, by means of
# pcs property set stonith-enabled=false
Otherwise, all the resources remain stopped.
I created a fencing resource for the partition that I am
sharing across the the nodes, by means of DRBD. This
works fine - but I still have the same problem as above -
i.e. when stonith-enabled is set to true, all the
resources get stopped, and remain in that state.
I am very confused here. Can anybody point me in the
right direction out of this conundrum?
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