Jenkins EC2 Docker install

# Get package updates
sudo yum update -y

# Check if docker installed
installed=`yum list installed | grep docker`

if [[ -z "${installed}" ]]; then
  # Docker install steps required for AMI (Amazon Linux)
  sudo yum install docker -y
  sudo service docker start
  sudo usermod -a -G docker ec2-user

  # Group membership changes require new SSH shell session to pick up
  # It seems that Jenkins keeps the same SSH session used during init open for running jobs.
  # Without new SSH session or login/logout, Jenkins user (ec2-user) is not in the docker group.
  # 
  # Current hack: Reboot after install to force new session, then skip Docker install + reboot on resulting Jenkins retry
  sudo reboot
else
  echo "Docker is already installed. Proceeding."
fi