Ping is not a service check
A server that answers ping shows that the network and the kernel are up. It does not show whether PostgreSQL is listening, whether the mail server came back after a restart, or whether a worker is bound to its port.
Services fail independently of the server, so a reachable server can still have services that are down.
What a port check confirms
A port check confirms that something is accepting connections on that port. For databases and mail servers, it is the most that can be verified without authenticating.
It catches common failures: a service that did not start after a reboot, a process that crashed, or a firewall rule changed during other work.
Ports to monitor
Mail. Ports 25, 465 and 587. Mail failures are easy to miss, because messages simply stop arriving.
Databases. Port 5432 for PostgreSQL and 3306 for MySQL. If a database only accepts local connections, a check from outside correctly reports it as refused.
Caches and queues. Port 6379 for Redis. A failed cache often slows an application down instead of stopping it, which makes it harder to notice.
Custom services. WebSocket servers, game servers and internal APIs on non-standard ports.
Why port 22 is not supported
SSH cannot be monitored with a port check. Every connected server already has a connection test that checks SSH with the platform’s credentials, which confirms authentication, not only that the port is open.
A port check on port 22 would still pass for a server the platform can no longer sign in to, which would be misleading.
Limits of port checks
An open port does not guarantee a working service. A database can accept connections and still reject queries because its disk is full, and a mail server can accept connections and reject every message.
If a service speaks HTTP, use a website or API monitor, which can inspect the response. Port monitoring is for services where accepting a connection is all that can be checked from outside.
Frequently asked questions
- What does a port check do?
- It opens a TCP connection to a host and port, confirms the connection was accepted, and closes it. Nothing is sent or read.
- Why can I not monitor port 22?
- It is excluded on purpose. Each server’s connection test already checks SSH with the platform’s credentials, which verifies authentication rather than an open port.
- My database only allows local connections. Will this work?
- A check from outside will report the port as refused, which is correct. Port monitoring is for services that should be reachable from where the check runs.
- Does it confirm the service is working?
- No. It confirms that something accepted the connection. For services that speak HTTP, use a website or API monitor instead.
- Can I monitor a port on a server not connected to the platform?
- Yes. Any reachable host and port can be monitored.
Key points
- Confirms a service accepts connections
- Mail, databases, caches and custom ports
- Connects and closes; nothing sent or read
- Port 22 excluded; SSH is tested separately
- Use HTTP checks where a service supports them