MachineOf= fleet parameter behaviour

[Arthur Clément]

Hi,

I'm starting to build units workflow/dependencies to handle static volumes for my services so it might not be the perfect practice, but here is my problem :

I created a path unit to detect the presence of a volume. 

[Unit] 
Description=Presence of Repl 3 LVM 
DefaultDependencies=false 

[Path] 
PathExists=/dev/mapper/vol_rs_repl3-rs_repl3 
Unit=data-mongodb-repl3.mount 

[Install] 
WantedBy=data-mongodb-repl3.mount 

[X-Fleet] 
Global=true

I created a mount unit to mount the volume

[Unit] 
Description=Mount third bo replica volume 
After=data-mongodb-repl3.path 
Requires=data-mongodb-repl3.path 


[Mount] 
What=/dev/mapper/vol_rs_repl3-rs_repl3 
Where=/data/mongodb/repl3 
Type=xfs 
Options=rw,relatime,attr2,inode64,noquota 
DirectoryMode=0755

It's working well with "[X-Fleet] Global=true", the volume is mounted on the nodes wich have one. 

As expected, I can see this failed units on the nodes without volume, it's not a big problem :

data-mongodb-repl3.path active          waiting

data-mongodb-repl3.mount inactive        dead

I tried to use MachineOf=data-mongodb-repl3.path on the mount unit (doc : "MachineOf Limit eligible machines to the one that hosts a specific unit") in order to deploy the mount unit only on the nodes with running path unit and to limit the number of failed units. 

But it does not work, the unit is deployed randomly on one node of the cluster (and only one node), without considering the unit state/presence in MachineOf .

What do I miss about this parameter ?

Arthur

Arthur Clement

DevOps

Contact: acle...@runmyprocess.com

Website: Fujitsu RunMyProcess

     

[Stephan Z.]

Global=true is about scheduling only, not the active state. And since you have not made your second unit also global, fleet will only create one which is intended to run on the same machine as any scheduled unit "data-mongodb-repl3.path" (of which you have a lot).

You could use fleet tags to mark the machines with the correct disks.

Regards

 Stephan

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[Arthur Clément]

Ok, that make sense.

I started with two conditions

[X-Fleet] 
Global=true 
MachineOf=data-mongodb-repl3.path

but I hit "Error creating units: Global cannot be used with Peers". I understand the error, it's documented, but that's really the behaviour I want/need. 

I know I can use fleet metadatas but I find it too much static, I'd like to run my units as decoupled from my workers as possible. I'll find a way.

Thanks,

Arthur

Arthur Clement

DevOps

Contact: acle...@runmyprocess.com

Website: Fujitsu RunMyProcess