Obtaining Linux templates

As all Linux guests have OpenSSH Server preinstalled by default, you only need to make sure a Linux template has cloud-init installed.

The easiest way to get a Linux template with cloud-init installed is to obtain it from its official repository or build one with the diskimage-builder tool. You can also create a Linux template from an existing boot volume.

Limitations

The disk image is created with only the root user that has neither password nor SSH keys. You can use the user data and cloud-init methods to perform initial configuration tasks on VMs that will be deployed from the disk image, for example, create custom user accounts. For more options to customize a VM during boot, refer to the cloud-init documentation.

To build a Linux template

Install the diskimage-builder package:
```
# yum install diskimage-builder
```
For the RHEL 7 guest OS, download the cloud image from the Red Hat Customer Portal (login required) and execute:
```
# export DIB_LOCAL_IMAGE=<path_to_rhel7_image>
```
Execute the disk-image-create command to build a disk image with installed cloud-init for the desired Linux guest. For example:
```
# disk-image-create vm centos7 -t qcow2 -o centos7
```
where
- centos7 is the name of a guest OS. Can be one of the following: centos6, centos7, debian, rhel7, or ubuntu.
  
  By default, using the ubuntu element will create a disk image for Ubuntu 16.04. To build the Ubuntu 18.04 disk image, add the DIB_RELEASE=bionic to the command: DIB_RELEASE=bionic disk-image-create vm ubuntu -t qcow2 -o ubuntu18.
- -o sets the name for the resulting disk image file.
Upload the created disk image by using the vinfra tool to the compute cluster:
```
# vinfra service compute image create centos7-image --os-distro centos7 \
--disk-format qcow2 --file centos7.qcow2
```
where
- centos7-image is the name of a new image.
- centos7 is the OS distribution. Can be one of the following: centos6, centos7, debian9, rhel7, ubuntu16.04, and ubuntu18.04.
- centos7.qcow2 is the QCOW2-image created on step 3.

To deploy a virtual machine from the uploaded template

Create the user-data configuration file with a custom user account:
```
# cat <<EOF > user-data
#cloud-config
user: myuser
password: password
chpasswd: {expire: False}
ssh_pwauth: True
EOF
```
where myuser is the name of a custom user and password is a password for the account.
Launch the deployment of a VM from the disk image by using the configuration file as user data:
```
# vinfra service compute server create centos7-vm --flavor medium \
--network public --user-data user-data --volume source=image,\
id=centos7-image,size=10
```
where
- centos7-vm is the name of a new VM.
- user-data is the configuration file created in step 5.
- centos7-image is the image added to the compute cluster in step 4.