Nodes are initialized by the userdata.sh in the Infrastructure repository.

Each node is instantiated by Terraform with an /etc/environment file generated by userdata.sh. This file contains the most basic level of configuration for a node. Environment variables defined here are available to any systemd unit with the use of EnvironmentFile=/etc/environment in the [Service] section. All environment variables defined here are also available by default in the shell.

# /etc/environment
#
# This file is parsed by pam_env module
#
# Syntax: simple "KEY=VAL" pairs on separate lines
#
UUID=2078ffe0-e6cf-48ab-9422-c9ee48d0c884
ID=2078ffe0

ANSIBLE_REPO="git@github.com:psev/ansible"

HOSTNAME=build-development-2078ffe0
REGION=us-west-2
TAGS=base,build
DEPLOY=development

Also upon instantiation, Terraform adds an SSH Key to each node for access to GitHub. It then creates a systemd unit file called /etc/systemd/system/bootstrap.service which is started at the end of userdata.sh. Keep in mind that changes to this file require a redeployment of the node.

# /etc/systemd/system/bootstrap.service

[Unit]
Description=Ansible Bootstrap
Requires=network-online.target
After=network-online.target

[Service]
EnvironmentFile=/etc/environment

ExecStartPre=-/usr/bin/git clone \$${ANSIBLE_REPO} /root/ansible
ExecStartPre=/usr/bin/git -C /root/ansible pull

ExecStart=/usr/bin/ansible-playbook -i /root/ansible/inventory \
  /root/ansible/archlinux/bootstrap.yml \
  -e "ansible_python_interpreter=/usr/bin/python2"

The primary function of the bootstrap role is to run the systemd role which handles the configuration of the node's initilization system. It configures network interfaces, enables systmed-journal-gatewayd which can be used for centralized logging and provides environment variables for network details.

Configuration of services such as docker and unbound require the information about the node's network interfaces. This data is made available by environment.py and environment.service.

When run, environment.service invokes environment.py which uses the netifaces Python module to garner network interface addresses and also parses /etc/resolv.conf for domain name details write that data to /etc/environment.network.

# /etc/environment.network

HOST_DOMAIN_1=sugarush-development.us-west-2.aws
HOST_DNS_1=172.16.0.2
HOST_IP=172.16.0.36

Network details are accessible in systemd units by including EnvironmentFile=/etc/environment.network in the [Service] section.

The bootstrap process also handles a variety of other system level configuration by applying roles defined in it's meta section.

The ansible service is enabled at the end of the bootstrap process via the ansible timer. This service calls the primary playbook main.yml that uses the TAGS environment variable, which is a comma separated list, to apply various roles to a node. See the Pre Bootstrap section for an example.