Using check-tcp from the official check-plugin pack, you can monitor TCP servers with Mackerel. For installing the official check-plugin pack, please refer to Using the official check plugin pack for check monitoring.
Checking HTTP servers
Below are configurations for an HTTP application server that will send the request GET / HTTP/1.0\r\n\r\n and check to see if "OK Farm" is contained in the response. By assigning the option --escape, characters such as "\r" and "\n" contained in the argument of --send will be treated as newline characters.
Additionally, it it is possible to configure thresholds for how many seconds it takes to connect, and with the example below, a Warning alert will be created if connection takes more than 3 seconds, and a Critical alert if it takes more than 10 seconds.
[plugin.checks.tcp_app] command = ["check-tcp", "--hostname", "localhost", "--port", "5000", "--send", "GET / HTTP/1.0\r\n\r\n", "--escape", "--expect-pattern", "OK Farm", "--warning", "3", "--critical", "10"]
Using with an assigned service
Of course it's also possible to check servers that aren't HTTP servers. By assigning the --service option for several services, you can run standard checks without doing any complicated configurations. For example FTP would be configured as shown below.
[plugin.checks.ftp] command = ["check-tcp", "--service", "ftp", "-H", "localhost"]
This is equivalent to the configuration below.
[plugin.checks.ftp] command = ["check-tcp", "-H", "localhost", "--port", "21", "--expect-pattern", "^200", "--quit", "QUIT"]
Possible settings that can be assigned to --service are: FTP, POP, SPOP, IMAP, SIMAP, SMTP, and SSMTP.
For information regarding other options please refer to check-tcp --help and the README.
Source code
The source code for check-tcp is publicly available via the URL below.
https://github.com/mackerelio/go-check-plugins/tree/master/check-tcp
