Each container uses its own network namespace, so to check the network connection inside the container namespace you need to run command inside that namespace.

Luckily all containers in a Pod share the same network namespace, so you can add small sidecar container to the pod that print to the log open connections.

Alternatively, you can run netstat command inside the pod (if the pod has it on its filesystem):

kubectl get pods | grep Running | awk '{ print $1 }' | xargs -I % sh -c 'echo == Pod %; kubectl exec -ti % -- netstat -tunaple' >netstat.txt
# or
kubectl get pods | grep Running | awk '{ print $1 }' | xargs -I % sh -c 'echo == Pod %; kubectl exec -ti % -- netstat -tunaple | grep ESTABLISHED' >netstat.txt

After that you'll have a file on your disk (netstat.txt) with all information about connections in the pods.

The third way is most complex. You need to find the container ID using docker ps and run the following command to get PID

$ pid = "$(docker inspect -f '{{.State.Pid}}' "container_name | Uuid")"

Then, you need to create named namespace: (you can use any name you want, or container_name/Uuid/Pod_Name as a replacement to namespace_name)

sudo mkdir -p /var/run/netns
sudo ln -sf /proc/$pid/ns/net "/var/run/netns/namespace_name"

Now you can run commands in that namespace:

sudo ip netns exec "namespace_name" netstat -tunaple | grep ESTABLISHED

You need to do that for each pod on each node. So, it might be useful to troubleshoot particular containers, but it needs some more automation for your task.

It might be helpful for you to install Istio to your cluster. It has several interesting features mentioned in this answer

The easiest way is to run netstat on all your Kubernetes nodes:

$ netstat -tunaple | grep ESTABLISHED | grep <ip address of db provider>

The last column is the PID/Program name column, and that's a program that is running in a container (with a different internal container PID) in your pod on that specific node. There are all kinds of different ways to find out which container/pod it is. For example,

# Loop through all containers on the node with
$ docker top <container-id> 

Then after you find the container id, if you look through all your pods:

$ kubectl get pod <pod-id> -o=yaml

And you can find the status, for example:

  status:
    conditions:
    - lastProbeTime: null
      lastTransitionTime: 2018-11-09T23:01:36Z
      status: "True"
      type: Initialized
    - lastProbeTime: null
      lastTransitionTime: 2018-11-09T23:01:38Z
      status: "True"
      type: Ready
    - lastProbeTime: null
      lastTransitionTime: 2018-11-09T23:01:38Z
      status: "True"
      type: ContainersReady
    - lastProbeTime: null
      lastTransitionTime: 2018-11-09T23:01:36Z
      status: "True"
      type: PodScheduled
    containerStatuses:
    - containerID: docker://f64425b3cd0da74a323440bcb03d8f2cd95d3d9b834f8ca5c43220eb5306005d