Using cloud-init with User Data
This technical guide provides a step-by-step approach to using cloud-init in an OUTSCALE virtual machine (VM), to implement automation in the Cloud environment.
Indeed, when you create a VM in the OUTSCALE Cloud, you can transmit user data to this VM. These user data are used to execute scripts or automated configuration tasks.
Prerequisites
Ensure the following:
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This page assumes a knowledge of cloud-init. For a more general introduction to that tool, see Introduction to cloud-init.
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The VM must have a public DNS name, accessible from the Internet.
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The security group of the VM must authorize SSH, HTTP, and HTTPS connections.
By default, user data scripts and cloud-init directives are executed only on the first start cycle of the VM. |
Method of User Data Definition
You can define user data for your VM in different ways:
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With the Cockpit web interface
It is the latter method that will be used for the step-by-step approach in the rest of this page.
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By API request with a Base64-encoded text string
The following example shows how to specify the content of a local file as a Base64-encoded text string in a command-line request:
$ osc-cli api CreateVms \ --ImageId "ami-abcd1234" \ --KeypairName "my-key-pair" \ --VmType "tinav4.c1r1p2" \ --SubnetId "Subnet-abcd1234" \ --SecurityGroupIds "['sg-abcd1234']" \ --UserData "$(cat my_script | base64)"
For more information, see Installing and Configuring OSC CLI.
Step-by-Step Approach: User Data in Cockpit with MIME-type Files as Input
1/ Create a VM
Follow the VM creation procedure in the page Creating VMs, until you reach the User Data / Cloud-init screen.
In the next steps, we use a VM created from an Ubuntu OUTSCALE Machine Image (OMI).
2/ Write the User Data
Example 1: Modification of the Hostname (via text/cloud-config Content)
In this example, we request a modification of the hostname (implicitly using the set_hostname module of cloud_init_modules that is configured by default in the official Ubuntu OMI).
Content-Type: text/cloud-config; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment; filename="cloud-config.txt"
#cloud-config
##Update hostname at first boot
hostname: test-userdata
Example 2: Installation of Packages (via text/cloud-config Content)
In this example, we request the installation of the python-pip package. To do so, we must first enable the package-update-upgrade-install module (which is by default disabled in the official Ubuntu OMI) by explicitly calling the cloud_config_modules directive.
Content-Type: text/cloud-config; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment; filename="cloud-config.txt"
#cloud-config
cloud_config_modules:
- package-update-upgrade-install
package_update: true
cloud_final_modules:
- [scripts-user, always]
##Install python-pip package
packages:
- python-pip
Example 3: Writing to Files or to the Console Output (via text/x-shellscript Content)
In this example, we request the execution of some instructions defined in shell scripts (/bin/sh and /bin/bash):
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Writing to the console output (/dev/ttyS0)
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Writing to new files (/root/output.txt and /tmp/output.txt)
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Modifying existing files (/root/.bashrc and /root/.vimrc)
The text/x-shellscript content type provides the user script that the cloud_final_modules module of cloud-init must execute.
Content-Type: text/x-shellscript; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment; filename="userdata.txt"
#!/bin/sh
##Writing in file
echo "Hello there. This is written with append." >> /root/output.txt
##Writing to console
echo "Hello there." >> /dev/ttyS0
#!/bin/bash
##Writing in file
/bin/echo "Hello there." >> /tmp/output.txt
cat > /root/.bashrc <<EOF
set -o vi
unalias -a
alias ll='ls -l'
EOF
touch /root/.vimrc
cat > /root/.vimrc <<EOF
set t_ti= t_te=
set compatible
set expandtab ts=2 sw=2 ai
EOF
Example 4: Combination of text/cloud-config and text/x-shellscript Contents
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In this example, we request the execution of scripts by successively using the text/cloud-config and text/x-shellscript content types seen previously, in one multipart MIME-type file.
Content-Type: multipart/mixed; boundary="//"
MIME-Version: 1.0
--//
Content-Type: text/cloud-config; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment; filename="cloud-config.txt"
#cloud-config
package_update: true
# update hostname
hostname: test-userdata
--//
Content-Type: text/x-shellscript; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment; filename="userdata.txt"
#!/bin/bash
/bin/echo "Hello there." >> /tmp/output.txt
--//
In this combined case:
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Verification of the User Data
To verify the user data transmitted to the VM, you can connect to the VM and launch the following Curl command:
$ curl http://169.254.169.254/latest/user-data
To verify that the instructions are executed, you can check:
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The console output in Cockpit. For more information, see Viewing the Console Output of a VM.
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The logs of cloud-init, available in the file /var/log/cloud-init-output.log in the case of an Ubuntu VM.
VMs created from CentOS official OMIs do not include cloud-init-output.log.
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