Getting connection is unreachable at places like ArgoCD

This can be for many reasons, but the main culprit is usually CoreDNS issues.

Add the dnsutils pod to your nodes like so;

apiVersion: v1
kind: Pod
metadata:
  name: dnsutils-m1
  namespace: default
spec:
  containers:
  - name: dnsutils-m1
    image: registry.k8s.io/e2e-test-images/jessie-dnsutils:1.3
    command:
      - sleep
      - "infinity"
    imagePullPolicy: IfNotPresent
  restartPolicy: Always
  nodeSelector:
    kubernetes.io/hostname: m1.example.com
  tolerations:
  - key: "node-role.kubernetes.io/control-plane"
    operator: "Exists"
    effect: "NoSchedule"
---
apiVersion: v1
kind: Pod
metadata:
  name: dnsutils-w1
  namespace: default
spec:
  containers:
  - name: dnsutils-w1
    image: registry.k8s.io/e2e-test-images/jessie-dnsutils:1.3
    command:
      - sleep
      - "infinity"
    imagePullPolicy: IfNotPresent
  restartPolicy: Always
  nodeSelector:
    kubernetes.io/hostname: w1.example.com
  tolerations:
  - key: "node-role.kubernetes.io/control-plane"
    operator: "Exists"
    effect: "NoSchedule"
---
apiVersion: v1
kind: Pod
metadata:
  name: dnsutils-w2
  namespace: default
spec:
  containers:
  - name: dnsutils-w2
    image: registry.k8s.io/e2e-test-images/jessie-dnsutils:1.3
    command:
      - sleep
      - "infinity"
    imagePullPolicy: IfNotPresent
  restartPolicy: Always
  nodeSelector:
    kubernetes.io/hostname: w2.example.com
  tolerations:
  - key: "node-role.kubernetes.io/control-plane"
    operator: "Exists"
    effect: "NoSchedule"

Then exec to the pods like so;
kubectl exec -ti dnsutils-m1 -- bash

Then you can run loops like this to see if there are dropped connections;

clear; for a in {1..50}; do echo ===============================; dig google.com; sleep .5; done
# or
clear; for a in {1..50}; do echo ===============================; nslookup google.com | grep SERVFAIL; sleep .5; done