Docker entrypoint bash script that enables 12FA style environment variable configuration for apps using S3 for storage of the environment variables.

entrypoint.sh

#!/bin/sh
# Docker Entrypoint for running an application after using AWS instance data and
# the aws cli to fetch and source environment variable configuration from S3.
#
# tldr Required Environment Variables
# 
#  - CONFIG_S3_BUCKET: The name of the S3 bucket where the config lives
#  - SERVICE: The name of the service for retrieving the config
# 
# or
#
# - ENVIRONMENT: Set to development to bypass AWS environment config activity
#  
# The goal is to enable multiple environments (test, staging, prod, etc) to run
# off the same docker image allowing for a single task definition in ECS, etc.
#
# It requires that the EC2 instances that the docker containers are running on
# are tagged with a variable named "Environment" that defines which environment
# for the containers.
#
# If ENVIRONMENT is not "development", SERVICE must be set to the service name
#
# The CONFIG_S3_BUCKET environment variable must be set to the S3 bucket that
# the configuration data in the following path:
#
#   /${ENVIRONMENT}/${SERVICE}/env.vars
#
# Which would be accessible via the following S3 URL:
#
#  s3://${CONFIG_S3_BUCKET}/${ENVIRONMENT}/{SERVICE}/env.vars
#
# Requires the awscli python package/application installed
#
# Requires a IAM profile that has the following settings
# 
# {
# 	"Version": "2012-10-17",
# 	"Statement": [{
# 		"Sid": "Stmt1449201368000",
# 		"Effect": "Allow",
# 		"Action": [
# 			"s3:ListBucket"
# 		],
# 		"Resource": [
# 			"arn:aws:s3:::${CONFIG_S3_BUCKET}",
# 		]
# 	}, {
# 		"Sid": "Stmt1449201427000",
# 		"Effect": "Allow",
# 		"Action": [
# 			"s3:GetObject"
# 		],
# 		"Resource": [
# 			"arn:aws:s3:::${CONFIG_S3_BUCKET}/*",
# 		]
# 	}, {
# 		"Effect": "Allow",
# 		"Action": ["ec2:DescribeTags"],
# 		"Resource": ["*"]
# 	}]
# }
#
# Note to bypass the AWS environment, set the ENVIRONMENT env variable set to
# development.
#
if [ "${ENVIRONMENT}" -ne "development" ]
then
  # Get the information required to use S3 to sync the environment variable data
  INSTANCE=`curl -s http://instance-data/latest/meta-data/instance-id`
  REGION=`curl -s http://instance-data/latest/meta-data/placement/availability-zone | rev | cut -c 2- | rev`
  ENVIRONMENT="`aws ec2 describe-tags --filters "Name=resource-id,Values=${INSTANCE}" "Name=key,Values=Environment" --region ${REGION} --output=text | cut -f5`"

  # Copy the environment variables
  aws s3 cp s3://${CONFIG_S3_BUCKET}/${ENVIRONMENT}/${SERVICE}/env.vars /etc/profile.d/

  # Activate the environment variables for the execution of the application
  source /etc/profile.d/env.vars
fi

# Run the Docker CMD passed in
exec $@