Advanced : customized creation

Custom creation with cloud-init

You can customise your instance’s creation by providing a user data file.

Cloud-init package is used to manage the initialization of an instance using user data.
It can only act on user data of following types :

• include-once-url
• include-url
• cloud-config-archive
• upstart-job
• cloud-config
• part-handler
• shellscript
• cloud-boothook

The type defines how the data file should start:

• a data script will start with: #!
• an include file: #include
• a cloud configuration file (cloud-config): #cloud-config
• an upstart job: #upstart-job
• a cloud boothook: #cloud-boothook
• a part handler: #part-handler

In this documentation, we will focus on the cloud-config type.
But you can read more about the cloud-init documentation: https://cloudinit.readthedocs.io/en/latest/topics/format.html

Cloud-config file

Cloud-config is an easy way to define tasks to be performed when the instance is launched.

First, the file must begin with #cloud-config.

#cloud-config
# vim: syntax=yaml
# This is a cloud-config file for user-data

Installing packages

The packages keyword is used to install packages. To upgrade them, set package_upgrade to true.
Then, all you have to do is list the packages to install.

package_upgrade: true

packages:
  - aptitude
  - linuxlogo
  - vim
  - ssh
  - python
  - gcc
  - g++

Add users

By using keyword users, you can add users.
These users can then access the instance using their public key.

users:

  - name: "user1"
    gecos: "user 1"
    sudo: ['ALL=(ALL) NOPASSWD:ALL']
    groups: [ wheel , sudo ]
    homedir: "/home/user1"
    shell: "/bin/bash"
    ssh-authorized-keys: [ < public_key_user1 > ]
    
  - name: "ubuntu"
    sudo: ['ALL=(ALL) NOPASSWD:ALL']
    groups: [ wheel , sudo ]
    homedir: "/home/ubuntu"
    shell: "/bin/bash"
    ssh-authorized-keys: [ < public_key_user1 > , < public_key_user2 > ]
    
  - name: "user2"
    gecos: "user 2"
    sudo: ['ALL=(ALL) NOPASSWD:ALL']
    groups: [ wheel , sudo ]
    homedir: "/home/user2"
    shell: "/bin/bash"
    ssh-authorized-keys: [ < public_key_user2 > ]

File writing

It is possible to write files on first launch with write_files.
Then, please specify its content, its access path, its permissions and its owner.

write_files:

  - content: |
      #!/bin/bash
      var="Hello World"
      echo "$var"
    owner: root:root
    path: /home/ubuntu/hello.sh
    permissions: '0777'
    
  - content: |
      #!/bin/bash
      now="$(date)"
      computer_name="$(hostname)"
      echo "Current date and time : $now"
      echo "Computer name : $computer_name"
    owner: root:root
    path: /home/ubuntu/Hello/date.sh
    permissions: '0777'

Run commands

The runcmd keyword lists commands you want to run in a terminal.

runcmd:
  # Customize bash for user
  - echo "linuxlogo" >> /home/user/.bashrc
  - source /home/user/.bashrc
  # Run two previous scripts
  - bash /home/ubuntu/hello.sh
  - bash /home/ubuntu/Hello/date.sh

Final message

A final message can be displayed in the launch logs of an instance.
This will show that all the cloud-init correctly ran.

final_message: "The system is finally up, after $UPTIME seconds"

Create a custom instance

Creating a custom instance is done in the same way as for a basic instance.
Just add the user data file option (--user-data cloud-config).

$ openstack server create \
    --image <image> \
    --flavor <flavor> \
    --user-data cloud-config \
    --network <project>-int-net \
    --security-group <group> \
    --key-name <rsa-key> \
    <instance-name>

Create instance from volume

You can start an instance from a volume rather than an image.

For this, use the instance creation command $ openstack server create with the following options

• --block-device : allows to boot from an existing source (image, volume or snapshot).
  For example, booting instance from an image and attaching a non-bootable volume. Or create volume from an image, then launch an instance from that volume.
• --swap : joined a swap disk to instance.
• --ephemeral : joined an ephemeral disk to instance.