shankscoder / ec2-autostart

Automatically starts EC2 instances based on network traffic

ec2-autostart

EC2 instances only accrue instance hours when they are turned on. We can take advantage of this by shutting down instances when not in use and booting them on demand through our VPN. Like socket activation, but for whole instances!

autostart

autostart monitors for TCP SYN and ICMP (ping) packets on a Wireguard interface. When it receives these, it checks if the IP belongs to a stopped EC2 instance, and if so starts it.

Usage: autostart [wg0]

Instance tagging

autostart limits its search to EC2 instances that have a tag autostart=true set.

Permissions

autostart will automatically assume the IAM role of the EC2 instance. You should assign a policy with at least the following permissions:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "ec2:StartInstances",
                "ec2:DescribeInstances"
            ],
            "Resource": "*"
        }
    ]
}

RST suppression

TCP clients will automatically retry connections while the instance is booting, but connection refused (TCP RST) packets can occur if the system starts but the desired service is not yet started. To deal with this, autostart automatically creates iptables rules that suppress RST packets for 30 seconds after booting each instance.

autostop

autostop automatically shuts down an EC2 instance when there is no activity. It is designed for instances that are primarily used for SSH (or VSCode over SSH) and background tasks via screen.

Usage:

autostop [duration] [cmd]
    duration: Duration of inactivity before shutdown. E.g.: 10m
    cmd: Command to run to shutdown. E.g.: /usr/bin/systemctl poweroff

Example: /usr/bin/autostop 10m /usr/bin/systemctl poweroff

Ending inactive ssh sessions

Most default sshd configurations will not end inactive sessions, such as if you close your laptop without explicitly closing SSH or VSCode. The following lines in sshd_config will end these sessions (after roughly 3*60=180 seconds):

ClientAliveInterval 60
ClientAliveCountMax 3

Client configuration

Because EC2 instances take some time to boot (usually under 30s to receiving SSH connections), SSH needs to be configured to wait longer before timing out. You can set ConnectTimeout 30 in for a host in .ssh/config on the client to increase this timeout.