prometheus-conntrack exposes conntrack metrics for docker containers or kubelet pods.
For example, the series conntrack_workload_connections{destination="192.168.50.4:2375",container="my-container",protocol="TCP",state="ESTABLISHED"} 2 means that the container "my-container" has two connections established with tcp://192.168.50.4:2375.
You can run prometheus-conntrack in a container or run the binary directly.
$ go get github.com/tsuru/prometheus-conntrack
$ prometheus-conntrack --listen-address :8080 --docker-endpoint unix:///var/run/docker.sock
prometheus-conntrack will fetch running containers from the --docker-endpoint and
expose their outbound connections on :8080/metrics.
$ go get github.com/tsuru/prometheus-conntrack
$ prometheus-conntrack -engine kubelet --listen-address :8080
prometheus-conntrack will fetch running pods from the local kubelet