Cloud-init

Cloud-init scripts let you optionally automate the initialization of virtual machines.

Setting a cloud-init script

To set a cloud-init script, click on the "Click for more advanced options" green link when deploying your virtual machine.

This is the default cloudinit configuration we pass to the hypervisor:

#cloud-config
user: user
password: [your defined password]
chpasswd: {expire: False}
ssh_pwauth: True
package_update: True
package_upgrade: False

The script that you provide simply gets appended to the end of this file.

Examples

Example 1: Preventing the automatic update of NVIDIA drivers

NVIDIA drivers autoupdate on the first boot. Once this happens, they become unusable. By including this cloud-init script, you'll lock the NVIDIA driver versions so that they do not autoupdate

Objectives

Write a file using cloud-init write_files in base64 encoding that uses apt-mark to hold NVIDIA packages from being automatically updated
- The file will have the following contents: dpkg-query -W --showformat='${Package} ${Status}\n' | grep -v deinstall | awk '{ print $1 }' | grep -E 'nvidia.*-[0-9]+$' | xargs -r -L 1 apt-mark hold
Run a file

Process

We'll set this as our cloud-init script:

write_files:
  - encoding: b64
    path: /home/user/tensordock_scripts/prevent_update.sh
    permissions: '0644'
    content: ZHBrZy1xdWVyeSAtVyAtLXNob3dmb3JtYXQ9JyR7UGFja2FnZX0gJHtTdGF0dXN9XG4nIHwgZ3JlcCAtdiBkZWluc3RhbGwgfCBhd2sgJ3sgcHJpbnQgJDEgfScgfCBncmVwIC1FICdudmlkaWEuKi1bMC05XSskJyB8IHhhcmdzIC1yIC1MIDEgc3VkbyBhcHQtbWFyayBob2xk
    owner: user:user
runcmd:
  - bash /home/user/tensordock_scripts/prevent_update.sh

Debrief

Explanation:

First, our server will write the new file, prevent_update.sh, in the user's new tensordock_scripts directory
Then, our server run this file, locking in our NVIDIA driver versions to prevent autoupdates

Example 2: Hosting a website with Apache2

Objectives

Install a package through cloud-init packages
Write a file using cloud-init write_files in plaintext

Process

By default, the Apache2 webserver listens on port 80. As such, we'll first forward an external port into that internal port.

Then, we'll set this as our cloud-init script:

packages:
  - apache2
write_files:
  - path: /var/www/html/index.html
    permissions: '0644'
    content: |
      <html>
      <head>
        <title> TensorDock Marketplace VM </title>
      </head>
      <body style="font-family: 'Courier New', monospace;">
        <p> You've reached your <span style="color: green;">TensorDock</span> virtual machine!</p>
      </body>
      </html>
    owner: www-data:www-data

Note the indentation of the custom HTML we've defined above! When writing files, we must append four (4) spaces in front of each text block.

Debrief

Explanation:

First, our server will install the apache2 package
Then, our server will overwrite the we create an index.html file with the custom HTML we've defined

Now, let's try accessing our web server!

Example 3: Hosting a simple Docker container

Objectives

Host a simple Docker container through the Docker CLI

TensorDock operating system templates come preinstalled with Docker

Process

For networking, we forward an external port into an internal port in the virtual machine. Then, a Docker container forwards a virtual machine's port into its own internal network.

By default, the NGINX webserver listens on port 80 within the Docker container, but we can have the Docker container listen on any port. As such, we'll first forward an external port (e.g. 20018) into itself.

Then, we'll set this as our cloud-init script:

write_files:
  - path: /home/user/cloudinit_website/index.html
    permissions: '0644'
    content: |
      <html>
      <head>
        <title> TensorDock Marketplace VM </title>
      </head>
      <body style="font-family: 'Courier New', monospace;">
        <p> You've reached your <span style="color: green;">TensorDock</span> virtual machine!</p>
      </body>
      </html>
    owner: www-data:www-data
runcmd:
  - docker run -d --restart unless-stopped --stop-timeout 300 -v /home/user/cloudinit_website:/usr/share/nginx/html:ro -p 20018:80 --name default_container nginx

Note that we have our Docker container listen on port 20018 because we forwarded external port 20018 into the virtual machine on port 20018

Debrief

Explanation:

First, our server will write a file to a new directory containing our custom HTML
Then, our server will run a Docker container that passes through the directory of our HTML page into the NGINX contiainer
When users access the external port 20018, our hypervisor forwards that to the virtual machine's port 20018, and then Docker forwards that to the NGINX container on port 80

Now, let's try accessing our web server!

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