After completing this section, you should be able to configure an instance with run time customizations performed at launch.

Cloud-init is software that handles the early initialization of an instance. It is included in the rhel-guest-image RPM package, which is the base image provided by Red Hat. Administrators can use cloud-init to perform a range of tasks, some of which are described below.

You can invoke cloud-init with user-data, which is data provided by the user when an instance is launched. The provided instructions are read and parsed by cloud-init in order to customize the instance. OpenStack also implements instance management via cloud-init. Users can launch an instance in the Dashboard and use the Configuration tab to specify the customization to apply.

Figure 8.1: Customizing an instance while launching in the Dashboard

OpenStack converts the information into a format that cloud-init can read. The following chart shows the user-data flow, starting with the initial configuration to the resulting instance customization.

Figure 8.2: Customizing an instance using cloud-init

Cloud-init contains support for several data formats, making it more flexible.

user-data scripts are a convenient way for domain operators to send a set of instructions to the instance upon its creation. The script is invoked at the rc.local level, which is last in the boot process. The following example changes the message of the day, using a Bash script:

#!/bin/bash
echo "This instance has been customized by cloud-init at $(date -R)!" >> /etc/motd

As an alternative to using customization scripts, domain operators can specify customization in cloud-config syntax, which provides instructions in a human-friendly format. These instructions include:

The following example shows how to customize the system by adding a group that includes users, adding a new user, and running a set of commands.

#cloud-config
groups:
  - cloud-users: [john,doe]

users:
  - default
  - name: operator
    gecos: Domain Operator
    sudo: ALL=(ALL) NOPASSWD:ALL
    groups: users, admin
    ssh-import-id: None
    lock-passwd: true
    ssh-authorized-keys:
      - <SSH public key>

runcmd:
 - [ wget, "http://materials.example.com", -O, /tmp/index.html ]
 - [ sh, -xc, "echo $(date) ': hello world!'" ]

After the instances have been spawned, administrators can ensure the cloud-init instructions were successfully executed. Customization can include:

To confirm the correct operation of cloud-init, review the cloud-init log file. Cloud-init logs its operations to /var/log/cloud-init.log. To confirm the customization, review the system for the expected results.

For example, review /var/log/cloud-init.log to confirm that cloud-init ran.

[user@demo ~]$ sudo less /var/log/cloud-init.log
...
Jul 19 01:53:05 host-192-168-1-5 cloud-init: Cloud-init v. 0.7.6 finished at Sun, 19 Jul 2020 06:53:05 +0000. Datasource DataSourceOpenStack [net,ver=2].  Up 88.48 seconds

In the /etc/passwd file, verify that the nagios user was created.

[user@demo ~]$ grep nagios /etc/passwd
...
nagios:x:903:903::/home/nagios:/bin/bash

Use ps -ef to ensure that the httpd services are running.

[user@demo ~]$ ps -ef | grep httpd
root      1204     1  0 04:38 ?        00:00:00 /usr/sbin/httpd -DFOREGROUND
apache    1205  1204  0 04:38 ?        00:00:00 /usr/sbin/httpd -DFOREGROUND
apache    1206  1204  0 04:38 ?        00:00:00 /usr/sbin/httpd -DFOREGROUND
apache    1207  1204  0 04:38 ?        00:00:00 /usr/sbin/httpd -DFOREGROUND
apache    1208  1204  0 04:38 ?        00:00:00 /usr/sbin/httpd -DFOREGROUND
apache    1209  1204  0 04:38 ?        00:00:00 /usr/sbin/httpd -DFOREGROUND
cloud-u+  1258  1237  0 04:40 pts/0    00:00:00 grep --color=auto httpd

Use the systemctl command to ensure that the httpd service is active and enabled.

[user@demo ~]$ systemctl status httpd.service
● httpd.service - The Apache HTTP Server
  Loaded: loaded (/usr/lib/systemd/system/httpd.service; enabled; vendor preset: disabled)
  Active: active (running) since Sun 2020-07-19 04:38:38 EDT; 2min 26s ago
    Docs: man:httpd(8)
          man:apachectl(8)
 Main PID: 1204 (httpd)
   Status: "Total requests: 0; Current requests/sec: 0; Current traffic:   0 B/sec"
   CGroup: /system.slice/httpd.service
           ├─1204 /usr/sbin/httpd -DFOREGROUND
           ├─1205 /usr/sbin/httpd -DFOREGROUND
           ├─1206 /usr/sbin/httpd -DFOREGROUND
           ├─1207 /usr/sbin/httpd -DFOREGROUND
           ├─1208 /usr/sbin/httpd -DFOREGROUND
           └─1209 /usr/sbin/httpd -DFOREGROUND
...output omitted...