ec2-init

Minimalistic init script that is designed for any Linux with OpenRC/systemd/runit to automatically bootstrap EC2 instances in the way similar to cloud-init but without Python dependency (and a lot of other modules pulled by cloud-init).

The script has a minimal set of modules but can effectively initialize EC2 instances: allow remote access over SSH and run custom bootstrap scripts.

Dependencies

This shell script depends on:

• coreutils
• curl

Some Linux distributions could have these dependencies not installed, for example, Void Linux requires manual installation of curl.

This shell script supports these init systems:

• OpenRC
• systemd
• runit

Installation

Ensure that coreutils and curl are installed. Not all distros have them installed by default. For example, coreutils could be not installed if busybox is installed. For example, curl is not installed by default on Void Linux.

OpenRC

# install ec2-init/service file
curl -s https://raw.githubusercontent.com/sormy/ec2-init/master/ec2-init.openrc -o /etc/init.d/ec2-init
chmod +x /etc/init.d/ec2-init

# run ec2-init automatically
rc-update add ec2-init boot

systemd

# install ec2-init helper script
curl -s https://raw.githubusercontent.com/sormy/ec2-init/master/ec2-init.script -o /usr/sbin/ec2-init
chmod +x /usr/sbin/ec2-init

# install service file
curl -s https://raw.githubusercontent.com/sormy/ec2-init/master/ec2-init.service -o /etc/systemd/system/ec2-init.service

# run ec2-init automatically
systemctl enable ec2-init

runit

# install ec2-init helper script
curl -s https://raw.githubusercontent.com/sormy/ec2-init/master/ec2-init.script -o /usr/sbin/ec2-init
chmod +x /usr/sbin/ec2-init

# install service file
mkdir -m 755 -pv /etc/sv/ec2-init
curl -s https://raw.githubusercontent.com/sormy/ec2-init/master/ec2-init.runit -o /etc/sv/ec2-init/run
chmod 755 -v /etc/sv/ec2-init/run
ln -sfv /run/runit/supervise.ec2-init /etc/sv/ec2-init/supervise

# run ec2-init automatically
ln -sfv /etc/sv/ec2-init /etc/runit/runsvdir/default/

Usage

ec2-init script runs on every boot, however, it doesn't reinitialize the instance on every reboot. It initializes the instance only if instance ID from last run doesn't match with current instance ID. So, if you take an image from existing instance and then spawn a new instance using the same image, then ec2-init will detect change in instance ID and will run init again.

The location of lock file can be change using EC2_INIT_LOCK option.

By default ec2-init runs with 3 modules hostname, ssh and exec but the list of modules to execute can be changed using EC2_INIT_MODULES option.

The script uses curl to access EC2 instance metadata. It is not recommended to change curl options, but, if needed, it can be done using CURL option.

The log for init process is logged to /var/log/ec2-init.log. The location of log file can be changed using EC2_INIT_LOG option.

Module "hostname"

Module hostname sets local hostname based on EC2 metadata.

In most cases needed just to differentiate hosts by shell prompt after login into EC2 instance.

Module "ssh"

Module ssh imports ssh public keys into /root/.ssh/authorized_keys during boot (with default configuration).

Needed to login into EC2 instance using SSH keys provided in AWS console.

The location of target directory for .ssh/authorized_keys file can be changed using SSH_USER_HOME option or using SSH_USER_NAME option.

Module "exec"

Module exec runs shell script (if exists) from instance user data. It downloads instance user data, decodes it from base64, then executes it if there is a shebang #! localed on first line of user data.

Instance user data by default is downloaded and decoded to /var/lib/ec2-init.user-data but the location can be changed using EC2_INIT_USER_DATA option.

The output of executed shell script is also logged to /var/log/ec2-init.log.

Needed to programmatically initialize EC2 instance using customizable instance provisioning shell script.

Currently script assumes that IMDSv1 is used (IMDSv2 is not supported at this time).

Read more about EC2 instance user data: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/instancedata-add-user-data.html

Configuration

While ec2-init script has sane defaults, you still have an option to change some of them.

OpenRC

Create file /etc/conf.d/ec2-init and override any variables you want.

For example:

echo 'EC2_INIT_MODULES="ssh"' > /etc/conf.d/ec2-init

systemd

Edit service unit file /etc/systemd/system/ec2-init.service.

Add environment variables in [Service] section, for example:

[Unit]
Description=EC2 Init
After=network.target

[Service]
Type=oneshot
ExecStart=/usr/sbin/ec2-init
Environment="EC2_INIT_MODULES=ssh"

[Install]
WantedBy=multi-user.target

And then reload systemd: systemctl daemon-reload.

runit

Edit service unit file /etc/sv/ec2-init/run.

Export any changed variables before invoking /usr/sbin/ec2-init:

#!/bin/sh

export EC2_INIT_MODULES=ssh

if /usr/sbin/ec2-init; then
    sv down ec2-init
fi

Variables

Below is the list of all variables you can set.

Name	Default	Description
EC2_INIT_LOCK	/var/lib/ec2-init.lock	Init lock file path.
EC2_INIT_LOG	/var/log/ec2-init.log	Init log file path.
EC2_INIT_USER_DATA	/var/lib/ec2-init.user-data	Init user data.
EC2_INIT_MODULES	hostname ssh exec	Modules to execute on init.
SSH_USER_NAME	$(whoami)	User name for ssh init.
SSH_USER_HOME	autodetect using /etc/passwd	User home directory (ssh).
CURL	curl $CURL_OPTS	CURL and options.

Default CURL_OPTS: curl --silent --max-time 1 --retry-delay 1 --retry 10 --retry-all-errors --fail

Cleanup

Would like to cleanup created by ec2-init files?

rm /var/log/ec2-init.* /var/lib/ec2-init.*

License

MIT