Creating a Linux Template

Linux Templates should be prepared using this documentation in order to prepare your linux Instances for Template deployment. For ease of documentation, the Instance which you are configuring the Template on will be referred to as “Main Template”. The final product, as created and usable for deployment in Cloudstack, will be referred as “Final Template”. This guide will cover cloud-init setup and scripted setups where available. It is assumed that openssh-server is installed during installation.

An overview of the procedure is as follow:

1. Upload your Linux ISO.

   For more information, see “Adding an ISO”.

2. Create an Instance with this ISO.

   For more information, see “Creating Instances”.

3. Prepare the Linux Instance

4. Create a Template from the Instance.

   For more information, see “Creating a Template from an Existing Instance”.

System preparation for Linux

The following steps will provide basic Linux installation for templating of Centos and Ubuntu.

1. Update OS

   The next step update the packages on the Main Template.

   ~ CentOS

   yum update -y
   reboot
   

   ~ Ubuntu

   sudo -i
   apt-get update
   apt-get upgrade -y
   apt-get install -y acpid ntp
   reboot
   

2. Networking

   Set Template Network interface configuration to DHCP so Cloudstack infrastructure can assign one on boot.

   Warning

   For CentOS, it is mandatory to take unique identification out of the interface configuration file /etc/sysconfig/network-scripts/ifcfg-eth0. Any entries starting with <VALUE> should be removed.

   ~ Centos

   echo "DEVICE=eth0
   TYPE=Ethernet
   BOOTPROTO=dhcp
   ONBOOT=yes" > /etc/sysconfig/network-scripts/ifcfg-eth0
   

3. Hostname Management

   Set a generic name to the Template Instance during installation, this will ensure components such as LVM do not appear unique to a machine. It is recommended that the name of “localhost” is used for installation.

   hostname localhost
   echo "localhost" > /etc/hostname
   

4. Password management

   Note

   It is a good practice to remove any non root Users that come with the OS (such as ones created during the Ubuntu installation). First ensure the root user Account is enabled by giving it a password and then login as root to continue.

   Once logged in as root, any custom User can be removed.

   deluser myuser --remove-home
   

   User password management and reset cappabilities in GUI are available with:

   • Cloud-init integration

   • Adding Password Management to Your Templates /Legacy for non systemd systems only/

5. SSH keys management

   Cloudstack can create key pair and push certificates to Instances. This feature is available with:

   • Cloud-init integration

   • Implementing a SSH-Key bash script

6. Partition management

   Volumes can autorextend after reboot when partition is extended in the GUI. This feature is possible with Cloud-init integration.

7. User-data

   Cloudstack can push user-data during Instance creation. This feature is possible with Cloud-init integration.

8. Template cleanup

   Warning

   Cleanup steps should be run when all Main Template configuration is done and just before the shutdown step. After shut down Final Template should be created. If the Main Template is started or rebooted before Final Template creation all cleanup steps have to be rerun.

   • Remove the udev persistent device rules

     This step removes information unique to the Main Template such as Network MAC addresses, lease files and CD block devices, the files are automatically generated on next boot.

     ~ CentOS

     rm -f /etc/udev/rules.d/70*
     rm -f /var/lib/dhclient/*
     

     ~ Ubuntu

     rm -f /etc/udev/rules.d/70*
     rm -f /var/lib/dhcp/dhclient.*
     

   • Remove SSH Keys

     This step is to ensure all Templated Instances do not have the same SSH keys, which would decrease the security of the machines dramatically.

     rm -f /etc/ssh/*key*
     

   • Cleaning log files

     It is good practice to remove old logs from the Main Template.

     cat /dev/null > /var/log/audit/audit.log 2>/dev/null
     cat /dev/null > /var/log/wtmp 2>/dev/null
     logrotate -f /etc/logrotate.conf 2>/dev/null
     rm -f /var/log/*-* /var/log/*.gz 2>/dev/null
     

   • Set User password to expire

     This step forces the User to change the password of the Instance after the Template has been deployed.

     passwd --expire root
     

   • Clearing User History

     The next step clears the bash commands you have just run.

   history -c
   unset HISTFILE
   

9. Shutdown the Instance

   Shutdown the Main Template.

   halt -p
   

10. Create the Template!

    You are now ready to create the Final Template, for more information see “Creating a Template from an Existing Virtual Machine”.