Virtual Machine administration tips

How to mount remote filesystem with FUSE (Filesystem in USEr space) on CentOS or Ubuntu

On CentOS:  

You will need to install a few packages that are not available in the standard CentOS repository. So, you must enable the EPEL repo:

yum install epel-release -y 

- Install FUSE (Filesystem in USEr space) and SSHFS packages 

yum install fuse sshfs
- Load the FUSE module

modprobe fuse

- Confirm that the FUSE module is loaded 

lsmod | grep fuse
fuse                  84368    2

- Optionally, make sure the FUSE module is loaded upon a reboot 

echo "modprobe fuse" >> /etc/rc.local 

- Using SSHFS. Once the FUSE module is loaded, you can mount your remote partition using SSHFS:

sshfs user@remote_host:/remote_directory  /local_mount_partition

If you have configured the login via ssh key authorization, you can use the following command:

sshfs user@remote_host:/remote_directory  /local_mount_partition -o IdentityFile=<absolute-path-with-key>

Note: If appear the following error 

fuse: bad mount point `/local_mount_partition': Transport endpoint is not connected

execute:      sudo fusermount -u /local_mount_partition

On Ubuntu: 

First you have to install FUSE and SSHFS packages with the apt-get comand:

apt-get install fuse 

apt-get install sshfs

Once the FUSE module is loaded, you can mount your remote partition using SSHFS:

sshfs user@remote_host:/remote_directory  /local_mount_partition

If you have configured the login via ssh key authorization, you can use the following command:

sshfs user@remote_host:/remote_directory  /local_mount_partition -o IdentityFile=<absolute-path-with-key>

Note: If appear the following error 

fuse: bad mount point `/local_mount_partition': Transport endpoint is not connected

execute :  sudo fusermount -u /local_mount_partition

How to use and configure Docker in your virtual machine

To use Docker in your virtual machine please set the MTU value at 1400 in the file  /etc/docker/daemon.json.  More in particular edit the file /etc/docker/daemon.json and then set

• • • {

      "mtu" : 1400

      }

Rescue a Virtual Machine

Instance rescue provides a mechanism for access, even if an image renders the instance inaccessible. Two rescue modes are currently provided.

Ephemeral Virtual Machine

The steps needed to rescue an inaccessible ephemeral virtual machine on ADA Cloud are:

Step 0.

• Create a rescuer virtual machine with a new key pair. Although this is not a fixed rule, it is suggested to create the rescuer machine using an image with same OS as the one on the inaccessible machine (same version or newer).
  

• Login to the rescuer and update it. As an example, for Ubuntu virtual machines:
  

  sudo apt update
  sudo apt upgrade

• Logout the rescuer and create a snapshot image of this virtual machine.

Step 1.

• Select the instance you want to rescue and from the drop-down menu on the right select "rescue instance":
  • In the menu that appears, select the image you just created from the rescuer machine.
• Login via ssh to the broken machine using the rescuer username/key 

• Check that the boot of the machine has been correctly executed using the command
  

  lsblk

  you should see the rescuer machine (/dev/vda1) mounted and the inaccessible machine on the device /dev/vdb1

• Mount such device /dev/vdb1 
  

  sudo mkdir /mnt/inaccessible_vm
  sudo mount /dev/sdb1 /mnt/inaccessible_vm

• Now you can access the files in the inaccessible machine to fix the problems (lsblk, fsck, xfs_repair, chroot, etc.) or backup important data
• Once the operation is done, logout the virtual machine and from the Dashboard select "unrescue".
  

Virtual Machine booted from a Bootable Volume

The steps needed to rescue an inaccessible VM instantiated from a bootable volume on ADA Cloud are:

Step 0.

• Shutdown the instance.
  

• In the tab "Volumes", track which secondary volumes are attached to the VM to be rescued and detach them.

• IMPORTANT: verify that the bootable volume won't be erased when deleting the VM!

  • To do this check, execute the command "openstack server show <id-vm-to-be-rescued>", have a look in the field "volumes_attached" and check that all the volumes listed have the property "delete_on_terminations='False' ". 
  • NB: In case you don't have access to the OpenStack CLI, please contact superc@cineca.it

• Keep track of the Flavor, Security Groups and FIP associated with the VM (FIP in particular if there is a DNS association).

• Delete the instance.

Step 1.

• Create a throwaway VM, attach the bootable volume to rescue as a secondary volume and associate a FIP to such VM.
  

• Login via ssh to the throwaway VM and execute all the needed operations on the volume to rescue (lsblk, fsck, xfs_repair, chroot, etc.).

• Once the volume has been recovered, exit the throwaway VM and detach the secondary volume that has been rescued.

• Restart the VM from the rescued bootable volume, reattaching the secondary volumes, FIP, and check the problem has been solved.

Resize a VM (a.k.a. change its flavor) 

Users are able to resize autonomously their VM, but, since there is a bug in actual version the OpenStack Horizon in ADA cloud, this operation can be done only via OpenStack CLI. 

Before to perform the resize operation: 

1. The VM must be shut off.  

2. If there are encrypted LUKS VOLUMES attached to the virtual machine, it is mandatory that the user:

   • Unmount the volumes from the VM

   • Detach the volumes from the Openstack Dashboard

To resize a VM, it is necessary to:

• Identify the VM ID:

  openstack server list --all | grep <VM_name>
  openstack server show < vm_ID > | grep flavor

• Identify the ID of the new flavor the VM needs:

  openstack flavor list

  • In the case of an Ephemeral VM, check the size of root disk of the original VM. Don't resize the VM if the new flavor has a disk smaller than the current one.

  • In the case of a VM with a Bootable Disk, the resize will affect only VCPUs number and RAM. The bootable disk will not be changed by the operation.

• Perform the resize, remembering to alert the user of the VM's temporary shutdown during the operation.

  openstack server resize --flavor <new_flavor_ID> --wait <vm_ID>

• Wait then the operation to "Complete"; at the same time, on the Openstack Dashboard the message "Confirm" will appear next to the server name.  Then use the command:

  openstack server resize confirm <vm_ID>

  Issue the resize confirmation in a separate command, since the option --confirm  on the command openstack server resize  is deprecated.

• Verify the success of the operation. Since the Dashboard can have visualization bugs, it is best to check via CLI:

  openstack server show < vm_ID > | grep flavor

• Ask the user to confirm the success of the operation. To do that they will need to boot the VM, login, and verify the VCPUs number and Memory size are correct with the following commands:

  cat /proc/cpuinfo
  free -g