[ClusterLabs] Antw: [EXT] Move a resource only where another has Started

[Ulrich Windl]

>>> martin doc <db1280 at hotmail.com> schrieb am 07.10.2021 um 17:45 in
Nachricht
<PS2P216MB054698C69A1951F0715E5074C2B19 at PS2P216MB0546.KORP216.PROD.OUTLOOK.COM>:

> Hi,
> 
> I've been trying to work out if it is possible to leave a resource on the 
> cluster node that it is on and only move it to another node if a dependent 
> resource is started. This is all using Red Hat's presentation in RHEL...
> 
> Ok, that might sound gibberish...
> 
> The cluster config I'm trying to build starts out with a basic ping:
> 
> pcs resource create MyGw ocf:pacemaker:ping host_list=192.168.1.254 
> failure_score=1 migration‑threshold=1
> pcs resource clone MyGw globally‑unique=true
> 
> and lets assume that there's three nodes, node1, node2, and node3 so the 
> above gets pacemaker running MyGw‑clone on both node1, node2, and node3. (3

> nodes makes it more interesting ;)
> 
> All good.
> 
> Now lets add a VIP into the mix and set it to run where MyGw‑clone is 
> running:

Hi!

As Ken already explained, you probably want to run your resource not where the
test is running, but where the test was sussessul.
That made me wonder: Does anybody use "node colors"? The idea would be: Ping
your gateway, and if that ping fails, the node should have major connectivity
problems.
Thus color the node yellow or red, and take resource actions depending on the
node color.

Anybody using that?

> 
> pcs resource create VIP ocf:heartbeat:IPaddr2 ip=192.168.1.1 nic=eno3 
> cidr_netmask=24
> pcs constraint colocation add VIP with MyGw‑clone
> 
> All good. Now comes the fun part. I want to run my own app only on one node

> and only where the gateway is:
> 
> pcs resource create App ocf:internal:app
> pcs constraint colocation add App with VIP
> 
> If the VIP is on node1 and MyGw‑clone is on node1 and running successfully 
> then so too will App. The problem starts when I unplug eno3 (not the same
NIC 
> as is used for the cluster mgmt.)
> 
> As soon as the ping fails, MyGw‑clone stops on node1 and this forces both
VIP 
> and App onto another node.
> 
> The problem is that pacemaker will eventually expire the failure and then 
> decide to restart MyGw‑clone on node1 and at the same time, stop VIP & App
on 
> node2. It then tries to start both VIP and App on node1.
> 
> What I'd really like to happen is for VIP & App to only move back to node1
if 
> and when MyGw‑clone is in the "Started" state (i.e. after a successful
ping). 
> i.e. to only do the "Move" of VIP&APP after the recovery of MyGw:0 has been

> successful.
> 
> If I set "failure_timeout" to be 0 then both App & VIP will stay put, and
the 
> cluster never again tests to see if MyGw:0 is healthy until I do a "pcs 
> resource cleanup."
> 
> I've tried colocation rules, but I wasn't any more successful with those 
> than the basic constraint configuration (assuming I got those right.)
> 
> I suppose another way to go about this would be to run another clone'd 
> resource that mimics the ping and automatically runs a "resource cleanup 
> MyGw‑clone" if it notices the clone is down on and node and the ping would 
> succeed. But is there a cleaner way?
> 
> Thanks,
> D.