Most uptime monitoring stops at the website. But the website is the last thing to fail; the database, the cache and the box you SSH into fail first and quieter. You can monitor all of them from the outside, with nothing installed, because nearly every network service introduces itself the moment you connect.
Services that speak first
- SSH sends a line like
SSH-2.0-OpenSSH_9.6before any login attempt. - FTP answers
220with a greeting. POP3 says+OK; IMAP says* OK. - MySQL and MariaDB send a handshake packet containing the server version — before authentication.
- PostgreSQL answers a one-byte question about TLS support with a one-byte reply.
- Redis responds to
PINGwithPONG— or withNOAUTH, which is also proof it is up.
A monitor connects, reads that first response, confirms it looks like the right protocol, and records the version. No credentials, no agent, no load on the service beyond one connection. If the response doesn't arrive or doesn't look right, the service is down or something else has taken its port.
The alert almost nobody has
That version string is more useful than it looks. An sshd that reports a different version than it did yesterday means one of two things: someone upgraded it, or something replaced it. You know which. A database that suddenly reports a different major version is a migration you did or a surprise you didn't. Alerting when the banner changes turns a reachability check into a lightweight security signal — and it costs nothing extra to collect.
One practical detail: some services embed session data in their greeting — a client address, a connection id, the time. A naive comparison would alert on every check. The comparison has to strip that noise and compare only what should be stable.
Redis, specifically
If a Redis server answers PONG to an unauthenticated PING from the internet, that is worth knowing urgently, for a different reason than uptime. A good monitor says so rather than just reporting "up".
Only monitor what's yours
Reading a banner is harmless on a server you control and unwelcome on one you don't. Use this on your own infrastructure, or where you have permission.
Doing it
UpConduit monitors SSH, FTP, IMAP, POP3, MySQL, PostgreSQL and Redis this way, records the version each reports, and alerts once when it changes. It works from a hostname or host:port, on every plan.