Ensure support for x86-64-v2 when creating VMs for each node

[fc7]

This is a small but I believe meaningful enhancement request.

I am using RHEL 9 as host. With several container images, I have encountered the following issue at runtime:

Fatal glibc error: CPU does not support x86-64-v2

Based on this I checked that my CPU (Xeon E5-1650 v3) does actually satisfy the criteria for x86-64-v2:

# /lib64/ld-linux-x86-64.so.2 --help
<snip>
Subdirectories of glibc-hwcaps directories, in priority order:
  x86-64-v4
  x86-64-v3 (supported, searched)
  x86-64-v2 (supported, searched)

The problem can actually be fixed by modifying the CPU settings of each VM to use the host-model. See e.g. here. With my compact setup (3 master/worker nodes), I used the following command:

for n in $(seq 0 2); do
    sudo virt-xml ocp4-master-${n} --edit --cpu host-model
done

After restarting each VM, the issue no longer appears.

I believe it would make sense to set this automatically with the playbook already at cluster creation, when setting up the VMs of each node.

[tomazb]

Yes, this is also needed for ACS as qemu64 is not the right CPU for the job :-)

[rbo]

You can overwrite the cpu in your cluster.yml via:

compute_special_cpu: "<cpu mode='host-passthrough'></cpu>"
master_special_cpu: "<cpu mode='host-passthrough'></cpu>"

I will double check if it make sense to change the defaults because of newer os/qemu version

[fc7]

I believe host-passthrough has the same meaning as host-model. IMHO it would make sense to make this the default. Otherwise many containers may end up in a crashloop because of the glibc incompatibility.

[sluetze]

+1 for making it default and also the options should be documented outside of the container native virtualization usecase, since they are needed for usecases outside of nested virtualization.

[rbo]

For testing purpose, I added <cpu mode='host-passthrough'></cpu> as default as branch libvirt-xml-improvements

[rbo]

Branch libvirt-xml-improvements merged into devel.

[rbo]

Released in 2023-06-22