[ClusterLabs] Antw: [EXT] Resolving cart before the horse with mounted filesystems.

[Ulrich Windl]

>>> Matthew Schumacher <matt.s at aptalaska.net> schrieb am 30.04.2021 um 16:26 in
Nachricht <48d6dd35-25bd-71ae-8263-f4ae11dd376d at aptalaska.net>:
> I have an issue that I'm not sure how to resolve so feedback is welcome.
> 
> I need to mount a local NFS file system on my node before I start a 
> VirtualDomain resource which depends on it, however, the NFS server is 
> itself a resource on the cluster.

This is phasees as "NFS loop mount" (the server mounting ist own export).

> 
> This causes the cart before the horse.  If I insert a node into a 
> running cluster, this is pretty simple, mount nfs before starting 
> pacemaker, and if a VirtualDomain resource is immediately started, we 
> already have what we need.  But that doesn't work on a cold cluster 
> because if I try to mount NFS on the node before the cluster starts the 
> NFS server, the mount fails.  If I always mount NFS after I start 

That's what the "bg" (background) option is for.

> pacemaker, then pacemaker will usually try to start VirtualDomain 
> resources before I can get further in the boot and mount NFS which 
> causes the VirtualDomain resource to fail to start.
> 
> I think I need one of the following fixes:
> 
> 1.  Delayed start on VirtualDomain resources so that we give time to get 
> the file system mounted which feels hackish as it's the old sleep fix 
> for race conditions.
> 
> 2.  Make the nfs mount itself a resource and make VirtualDomain 
> resources depend on it.  In order for this to work each node would need 

Naturally it would be a cluster resource.

> it's own nfs mount resource, and VirtualDomain resources that can run on 
> any node would need to depend on the nfs mount resource of whatever node 
> they decide to run on but not the nfs mount resource of any other node.  
> I'm not sure how to make this work because the dependency changes with 
> what node the VirtualDomain resource is started on.

You could also try a PING node for the NFS, and start only after the ping restuirns success.

> 
> 3.  Make the VirtualDomain resource call a script on start/migrate that 
> simply looks for the nfs mount, and if missing, try to mount. This seems 
> less hackish, but will ensure that we always try to get the nfs mount 
> going the first time the resource is moved/started there.

Too complex IMHO.

> 
> Any ideas or thoughts would be very helpful and appreciated.

Regards,
Ulrich

> 
> Matt
> 
> 
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