cron-ngrok

Uses ngrok to establish an SSH tunnel, with configurable abort timeouts and session timeouts. Notifies Slack URL of connection establishment.

Runnable from a RaspberryPI. Cuz that's what I'm doing.

Dependencies

• curl
• timeout (or gtimeout on MacOS X -- installable via brew install coreutils)
• ngrok (of course)
• a Slack webhook for notifications

Configuration

It's probably a good idea to first get an auth token for ngrok (just go to the website and sign up). Then follow the one-liner to write your auth token to your ngrok.yml file.

Configuration is mostly straightforward, but kind of (read: very) wonky still. You can configure this script with a tun.conf file in the same directory as this script (um, not secure at all - it gets sourced), or you can configure via environment variables.

Generally, all environment variables precede values in tun.conf -- except for NOTIFY_URL (i.e. the Slack URL). Yeah, that's weird but this whole script was a hack anyway so I'm not fixing this. Deal with it. But anyhow, if you're configuring by environment variables anyway, you probably don't need to use a tun.conf.

Environment Variables in tun.conf

export KEEPALIVE="900" # number of seconds to keep an established tunnel open (15 min default)
export ABORT_AFTER="60" # connection timeout in seconds before disconnecting on failure
export MONITOR_LOG="/tmp/ngrok.log" # the log to monitor for ngrok events; used to detect a successful tunnel
export NOTIFY_URL="..." # the Slack endpoint to receive notifications
export TZ=":America/Los_Angeles" # sets the time zone for timestamps - otherwise this will probably output UTC

crontab notes

First off, I configured this script in my user crontab, not as root. root is simply not necessary with ngrok.

If you have ngrok installed in a directory that's added to your PATH from within .bashrc or .bash_profile, remember to invoke the script with bash -l, like so: /bin/bash -l /path/to/mktun.sh >> /path/to/the.log. In fact, just do that anyway so ngrok will automatically pick up your ngrok.yml file in your homedir.

Be wary of the append redirect >> unless you have logrotate configured. Might be just good enough to do >, which is what I did -- I only care about the last run.

Why?

I'm about a hour or so drive away from a small office network that I'm managing for a family member. Sometimes the ISP "technicians" come by and jack up the router settings (e.g. factory reset) when connectivity sucks (unfortunately that office is stuck on AT&T for the time being), and I lose my port forwards. I don't want to drive all the way to the office to open up ports again. Nobody in the office is technical, or reliable enough to be "remote hands."

Oh the horror!

Yes, this seems like a very not great idea from a security standpoint. But this is MIT licensed, so you can't sue me for this shit. You've been warned.

I'm saving on gas and time that could be better spent at a pub.

KTHXBAI.