Cannot execute netcat inside a Docker/Kubernetes container - kubernetes

Question

I am trying to deploy a few Docker containers via Kubernetes within an AWS cluster. I have no problems with the deployment itself, but I am unable to execute netcat from inside a container.
If I enter the container (kubectl exec -it example-0 bash) and I attempt to execute: nc -w 1 -q 1 127.0.0.1 2181, it fails with:
(UNKNOWN) [127.0.0.1] 2181 (?) : Connection refused
This becomes a problem for some of my containers because I am using the netcat command to implement the corresponding readiness probes.
Example:
Deploying a Zookeeper container:
apiVersion: apps/v1
kind: StatefulSet
metadata:
name: zookeeper
labels:
app: zookeeper
spec:
serviceName: zookeeper
replicas: 1
selector:
matchLabels:
app: zookeeper
template:
metadata:
labels:
app: zookeeper
spec:
terminationGracePeriodSeconds: 1800
nodeSelector:
proc_host: "yes"
host_role: "iw"
containers:
- name: zookeeper
image: imageregistry:443/mydomain/zookeeper
imagePullPolicy: Always
ports:
- containerPort: 2181
name: client
- containerPort: 2888
name: peer
- containerPort: 3888
name: leader-election
resources:
limits:
memory: 120Mi
requests:
cpu: "10m"
memory: 100Mi
lifecycle:
preStop:
exec:
command: ["sh", "-ce", "kill -s TERM 1; while $(kill -0 1 2>/dev/null); do sleep 1; done"]
env:
- name: LOGGING_LEVEL
value: WARN
- name: ID_OFFSET
value: "4"
- name: POD_IP
valueFrom:
fieldRef:
fieldPath: status.podIP
readinessProbe:
exec:
command:
- /bin/bash
- -c
- '[ "imok" = "$(echo ruok | nc -w 1 -q 1 127.0.0.1 2181)" ]'
initialDelaySeconds: 15
timeoutSeconds: 5
volumeMounts:
- name: zookeeper
mountPath: /tmp/zookeeper
volumes:
- name: zookeeper
hostPath:
path: /var/lib/kafka/zookeeper
and it deploys fine, but the readiness probe fails with the following error:
Readiness probe failed: (UNKNOWN) [127.0.0.1] 2181 (?) : Connection refused
I am new to Kubernetes, does anybody know what I am missing?
Thank you for your help.