Tiny Cloud

The Tiny Cloud bootstrapper performs critical initialization tasks for cloud instances during their first boot. Unlike the more popular and feature-rich cloud-init, Tiny Cloud seeks to do just what is necessary with a small footprint and minimal dependencies.

A direct descendant of tiny-ec2-bootstrap, Tiny Cloud works with multiple cloud providers. Currently, the following are supported:

• AWS (Amazon Web Services)
• Azure (Microsoft Azure)
• GCP (Google Cloud Platform)
• OCI (Oracle Cloud Infrastructure)
• NoCloud (cloud-init's NoCloud AWS-compatible data source)

Features

The following actions will occur only once, during the initial boot of an instance:

• expand the root filesystem to use all available root device space, during the sysinit runlevel
• set the instance's hostname from instance metadata
• install SSH keys from instance metadata to the cloud user account's authorized_keys file (the user must already exist)
• save the instance user-data to a file, and if it's a script, execute it at the end of the default runlevel

Optional features, which may not be universally necessary:

• manage hotpluggable network interfaces
• sync IMDS-provided secondary IPv4 and IPv6 addresses network interfaces
• manage symlinks from NVMe block devices to /dev/xvd or /dev/sd devices (i.e. AWS Nitro instances)

Also included is a handy imds client script for easy access to an instance's IMDS data.

Requirements

As Tiny Cloud is meant to be tiny, it has very few dependencies:

• Busybox (ash, wget, etc.)
• ifupdown-ng (optional, for network management)
• iproute2-minimal (optional, for syncing IPv4/IPv6 from IMDS)
• nvme-cli (optional, for AWS nitro NVMe symlinks)
• partx
• resize2fs
• sfdisk
• yx (optional, allows NoCloud to extract metadata from YAML files)

Tiny Cloud has been developed specifically for use with the Alpine Cloud Images project, and as such, it is currently tailored for use with Alpine Linux, the OpenRC init system, and the ext4 root filesystem. If you would like to see Tiny Cloud supported on additional distributions, init systems, and/or filesystems, please open an issue with your request -- or better yet, submit a merge request!

Installation

Typically, Tiny Cloud is installed and configured when building a cloud image, and is available on Alpine Linux as the tiny-cloud APKs...

apk add tiny-cloud-<cloud>

This will install the necessary init scripts, libraries, etc. plus any missing dependencies for Tiny Cloud to support <cloud>.

Alternately, you can download a release tarball, and use make to install it.

Next, enable the three primary init scripts...

rc-update add tiny-cloud-early sysinit
rc-update add tiny-cloud default
rc-update add tiny-cloud-final default

Configuration

By default, Tiny Cloud expects configuration at /etc/tiny-cloud.conf, The stock lib/tiny-cloud/tiny-cloud.conf` file contains details of all tuneable settings.

Because Tiny Cloud does not currently do auto-detection, you MUST set a configuration value for CLOUD indicating which cloud provider will be used. Current valid values are aws, azure, gcp, oci, and nocloud.

Operation

The first time an instance boots -- either freshly instantiated from an image, or after installation on a pre-existing instance -- Tiny Cloud sets up the instance in three phases...

Early Phase

The tiny-cloud-early init script does not depend on the cloud provider's Instance MetaData Service (IMDS), and therefore does not have a dependency on networking. During this "early" phase, the root filesystem is expanded, and any necessary mdev rules for device hotplug are set up.

Main Phase

The main tiny-cloud init script does depend on the cloud provider's IMDS data; it saves the instance's user data to /var/lib/cloud/user-data, sets up instance's hostname, and installs the cloud user's SSH keys before sshd starts.

If the user data is compressed, Tiny Cloud will decompress it. Currently supported compression algorithms are gzip, bzip2, unxz, lzma, lzop, lz4, and zstd. (Note that lz4 and zstd are not installed in Alpine by default, and would need to be added to the image.)

Final Phase

tiny-cloud-final should be the very last init script to run in the default runlevel.

If the user data is a script starting with #!/, it will be executed; its output (combined STDOUT and STDERR) and exit code are saved to /var/log/user-data.log and /var/log/user-data.exit, respectively; the directory is overrideable via the TINY_CLOUD_LOGS config setting.

If all went well, the very last thing tiny-cloud-final does is touch a .bootstrap-complete file into existence in /var/lib/cloud or another directory specified by the TINY_CLOUD_VAR config setting.

Skipping Init Actions

If you need to skip any individual init script actions (for example, if you have a different means to set the instance hostname), you can set the SKIP_INIT_ACTIONS config to a whitespace-separated list of actions to skip.

Further Reboots

After the initial bootstrap of an instance, the init scripts are largely a no-op.

To force the init scripts to re-run on the next boot...

rm -f /var/lib/cloud/.bootstrap-complete

or

service tiny-cloud incomplete

If you're instantiating an instance in order to create a new cloud image (using Packer, or some other means), you will need to do this before creating the image to ensure that instances using the new image will also run Tiny Cloud init scripts during their first boot.

Cloud Hotplug Modules

vnic_eth_hotplug

This hotplug module adds and removes ethernet interfaces as virtual NICs are attached/detached from the instance.

An ifupdown-ng executor also syncs the interfaces' secondary IPv4 and IPV6 addresses associated with those VNICs, if the cloud's IMDS provides that configuration data.

nvme_ebs_links

EBS volumes are attached to AWS EC2 Nitro instances using the NVMe driver. Unfortunately, the /dev/nvme* device names do not match the device name assigned to the attached EBS volume. This hotplug module figures out what the assigned device name is, and sets up /dev/xvd* and /dev/sd* symlinks to the right NVMe devices for EBS volumes and their partitions.

(deprecated, see CHANGELOG.md)