How to Monitor Docker Container Network Connections with check-docker-connection

The check-docker-connection utility monitors Docker container network connections, showing TCP and UDP connection counts and various connection states.

What is check-docker-connection

It lists the network connection status of specified containers, including ESTABLISHED, TIME_WAIT, FIN_WAIT2, CLOSE_WAIT, LISTEN, SYN_SENT, SYN_RECV, and UDP connection numbers. Users can specify containers by ID or name, or request the top N containers with the most connections. Results are displayed in a table for easy reading.

Main features

ESTABLISHED connections

TIME_WAIT connections

FIN_WAIT2 connections

CLOSE_WAIT connections

LISTEN state

SYN_SENT state

SYN_RECV state

UDP connection count

Environment requirements

Docker installed on the host netstat and nsenter commands (usually provided by the net-tools and util-linux packages)

Command‑line arguments

-c

: specify one or more container IDs or names (comma‑separated) -n: show the top N containers with the most connections

Note: -c and -n cannot be used together.

Running the tool

$ docker run --rm -v /var/run/docker.sock:/var/run/docker.sock --pid=host --net=host --privileged 80imike/check-docker-connection

Important flags:

The container needs access to the Docker socket, so /var/run/docker.sock is mounted. --pid=host and --net=host allow the container to see the host’s process and network namespaces. --privileged enables the use of nsenter inside the container.

Usage examples

Example 1 – monitor a single container

$ docker run --rm -v /var/run/docker.sock:/var/run/docker.sock --pid=host --net=host --privileged 80imike/check-docker-connection -c traefik

This prints all network connection states for the container named traefik.

Example 2 – monitor multiple containers

$ docker run --rm -v /var/run/docker.sock:/var/run/docker.sock --pid=host --net=host --privileged 80imike/check-docker-connection -c traefik,splayer

Shows the network connections for both traefik and splayer containers.

Example 3 – top N containers by connections

$ docker run --rm -v /var/run/docker.sock:/var/run/docker.sock --pid=host --net=host --privileged 80imike/check-docker-connection -n 3

Displays the three containers with the highest number of network connections.

These examples demonstrate how to quickly inspect Docker container network states for performance analysis and troubleshooting.