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57 lines
2.4 KiB
Markdown
57 lines
2.4 KiB
Markdown
# Tiny EC2 Bootstrapper
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This is designed to do the minimal amount of work required to bootstrap an EC2
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instance based on the local settings assigned at boot time as well as the
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user's configured settings. This is in-concept similar to
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[cloud-init](https://cloudinit.readthedocs.io/en/latest/) but trades features
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and cloud platform support for small size and limited external dependencies.
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## Requirements
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The most important feature of this bootstrapper is the very limited set of
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dependencies. In-fact this works with just busybox provided the wget applet is
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built-in. The only required dependencies are:
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- bash-like shell (e.g. bash, dash, ash)
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- wget
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## Supported Features and Environments
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cloud-init has support for many different cloud providers. This project only
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supports EC2, specifically the [EC2 metadata
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service](https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ec2-instance-metadata.html)
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is a hard requirement of using this bootstrapper. All of the data for the
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supported features below is sourced from the EC2 instance metadata service
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which runs on every EC2 instance at IP 169.254.169.254.
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cloud-init also has a very rich feature set with support for adding users,
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installing packages, and many other things. This bootstrap does not support
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those things. Instead it supports:
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- setting system hostname
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- install user's configured SSH keys to the alpine user's authorized_keys file
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- run any script-like user data (must start with #!)
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These steps only run once. After the initial bootstrap the bootstrapper script
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is a no-op. To force the script to run again at boot time remove the file
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`/var/lib/cloud/.bootstrap-complete` and reboot the instance.
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## User Data
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User data is provided at instance boot time and can be any arbitrary string of
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data. The bootstrapper will consider any user data that begins with the ASCII
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characters '#!' to be a script. It will write the entire contents of the user
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data to `/var/lib/cloud/user-data.sh`, make the file executable, and execute
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the file piping any output to `/var/log/cloud-bootstrap.log`.
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The user data script can do anything it pleases with the instance. It will be
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run as root and networking will be up. No other grantees about system state are
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made at the point the script runs.
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## Assumptions
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- This was written for Alpine Linux and thus assumes that the login user is
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called alpine. This could be configurable in the future but currently is not.
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- The script is run by OpenRC
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