TCP State Exporter is a simple service written in Go that exposes metrics about the state of TCP connections on a machine. It leverages Prometheus's client library to expose these metrics at a /metrics endpoint, which can then be scraped by Prometheus.

./tcp-state-exporter --port <port-number>

Use the -p or --port flag to specify the port number the metrics server should listen on. The default is 9112.

The -h or --help flag can be used to display a help message and exits.

The TCP State Exporter allows for the addition of dynamic labels to the metrics through environment variables that follow the EXPORTER_LABEL_ prefix. For instance, if you set an environment variable named EXPORTER_LABEL_app_name, this will append a app_name label to the metrics with its value set from the environment variable.

When you navigate to http://localhost:<port-number>/metrics, you will see output similar to the following:

# HELP tcp_connections Current number of TCP connections by state and remote address
# TYPE tcp_connections gauge
tcp_connections{remote_address="192.0.2.1", remote_port="12345", state="ESTABLISHED"} 1
tcp_connections{remote_address="192.0.2.2", remote_port="23456", state="SYN_SENT"} 1
tcp_connections{remote_address="192.0.2.3", remote_port="34567", state="TIME_WAIT"} 1

# HELP tcp_listening_ports Current number of TCP listening ports by local address
# TYPE tcp_listening_ports gauge
tcp_listening_ports{local_address="0.0.0.0", local_port="22"} 1
tcp_listening_ports{local_address="0.0.0.0", local_port="80"} 1

With the EXPORTER_LABEL_app_name environment variable set as illustrated earlier, your metrics output would also include the app_name label.