today while trying to run my pod , I discovered this error which we see in the describe events:

# kubectl describe pod monitor-prometheus-alertmanager-c94f7b6b7-tg6vc -n monitoring
Name:         monitor-prometheus-alertmanager-c94f7b6b7-tg6vc
Namespace:    monitoring
Priority:     0
Node:         kube-worker-vm2/192.168.1.36
Start Time:   Sun, 09 May 2021 20:42:57 +0100
Labels:       app=prometheus
              chart=prometheus-13.8.0
              component=alertmanager
              heritage=Helm
              pod-template-hash=c94f7b6b7
              release=monitor
Annotations:  cni.projectcalico.org/podIP: 192.168.222.51/32
              cni.projectcalico.org/podIPs: 192.168.222.51/32
Status:       Running
IP:           192.168.222.51
IPs:
  IP:           192.168.222.51
Controlled By:  ReplicaSet/monitor-prometheus-alertmanager-c94f7b6b7
Containers:
  prometheus-alertmanager:
    Container ID:  docker://0ce55357c5f32c6c66cdec3fe0aaaa06811a0a392d0329c989ac6f15426891ad
    Image:         prom/alertmanager:v0.21.0
    Image ID:      docker-pullable://prom/alertmanager@sha256:24a5204b418e8fa0214cfb628486749003b039c279c56b5bddb5b10cd100d926
    Port:          9093/TCP
    Host Port:     0/TCP
    Args:
      --config.file=/etc/config/alertmanager.yml
      --storage.path=/data
      --cluster.advertise-address=[$(POD_IP)]:6783
      --web.external-url=http://localhost:9093
    State:          Running
      Started:      Sun, 09 May 2021 20:52:33 +0100
    Ready:          False
    Restart Count:  0
    Readiness:      http-get http://:9093/-/ready delay=30s timeout=30s period=10s #success=1 #failure=3
    Environment:
      POD_IP:   (v1:status.podIP)
    Mounts:
      /data from storage-volume (rw)
      /etc/config from config-volume (rw)
      /var/run/secrets/kubernetes.io/serviceaccount from monitor-prometheus-alertmanager-token-kspg6 (ro)
  prometheus-alertmanager-configmap-reload:
    Container ID:  docker://eb86ea355b820ddc578333f357666156dc5c5a3a53c63220ca00b98ffada5531
    Image:         jimmidyson/configmap-reload:v0.4.0
    Image ID:      docker-pullable://jimmidyson/configmap-reload@sha256:17d34fd73f9e8a78ba7da269d96822ce8972391c2838e08d92a990136adb8e4a
    Port:          <none>
    Host Port:     <none>
    Args:
      --volume-dir=/etc/config
      --webhook-url=http://127.0.0.1:9093/-/reload
    State:          Running
      Started:      Sun, 09 May 2021 20:44:59 +0100
    Ready:          True
    Restart Count:  0
    Environment:    <none>
    Mounts:
      /etc/config from config-volume (ro)
      /var/run/secrets/kubernetes.io/serviceaccount from monitor-prometheus-alertmanager-token-kspg6 (ro)
Conditions:
  Type              Status
  Initialized       True 
  Ready             False 
  ContainersReady   False 
  PodScheduled      True 
Volumes:
  config-volume:
    Type:      ConfigMap (a volume populated by a ConfigMap)
    Name:      monitor-prometheus-alertmanager
    Optional:  false
  storage-volume:
    Type:       PersistentVolumeClaim (a reference to a PersistentVolumeClaim in the same namespace)
    ClaimName:  prometheus-pv-claim
    ReadOnly:   false
  monitor-prometheus-alertmanager-token-kspg6:
    Type:        Secret (a volume populated by a Secret)
    SecretName:  monitor-prometheus-alertmanager-token-kspg6
    Optional:    false
QoS Class:       BestEffort
Node-Selectors:  boardType=x86vm
Tolerations:     node.kubernetes.io/not-ready:NoExecute op=Exists for 300s
                 node.kubernetes.io/unreachable:NoExecute op=Exists for 300s
Events:
  Type     Reason     Age                    From               Message
  ----     ------     ----                   ----               -------
  Normal   Scheduled  9m54s                  default-scheduler  Successfully assigned monitoring/monitor-prometheus-alertmanager-c94f7b6b7-tg6vc to kube-worker-vm2
  Normal   Pulled     7m53s                  kubelet            Container image "jimmidyson/configmap-reload:v0.4.0" already present on machine
  Normal   Created    7m52s                  kubelet            Created container prometheus-alertmanager-configmap-reload
  Normal   Started    7m52s                  kubelet            Started container prometheus-alertmanager-configmap-reload
  Warning  Failed     6m27s (x2 over 7m53s)  kubelet            Failed to pull image "prom/alertmanager:v0.21.0": rpc error: code = Unknown desc = context canceled
  Warning  Failed     5m47s (x3 over 7m53s)  kubelet            Error: ErrImagePull
  Warning  Failed     5m47s                  kubelet            Failed to pull image "prom/alertmanager:v0.21.0": rpc error: code = Unknown desc = Error response from daemon: Get https://registry-1.docker.io/v2/: net/http: request canceled while waiting for connection (Client.Timeout exceeded while awaiting headers)
  Normal   BackOff    5m11s (x6 over 7m51s)  kubelet            Back-off pulling image "prom/alertmanager:v0.21.0"
  Warning  Failed     5m11s (x6 over 7m51s)  kubelet            Error: ImagePullBackOff
  Normal   Pulling    4m56s (x4 over 9m47s)  kubelet            Pulling image "prom/alertmanager:v0.21.0"
  Normal   Pulled     19s                    kubelet            Successfully pulled image "prom/alertmanager:v0.21.0" in 4m36.445692759s

then I tried to ping first with google.com since it was working I wanted to check https://registry-1.docker.io/v2/ so I tried to ping docker.io but I do not get ping result. what is causing this ?

osboxes@kube-worker-vm2:~$ ping google.com
PING google.com (142.250.200.14) 56(84) bytes of data.
64 bytes from lhr48s29-in-f14.1e100.net (142.250.200.14): icmp_seq=10 ttl=117 time=35.8 ms
64 bytes from lhr48s29-in-f14.1e100.net (142.250.200.14): icmp_seq=11 ttl=117 time=11.9 ms
64 bytes from lhr48s29-in-f14.1e100.net (142.250.200.14): icmp_seq=12 ttl=117 time=9.16 ms
64 bytes from lhr48s29-in-f14.1e100.net (142.250.200.14): icmp_seq=13 ttl=117 time=11.2 ms
64 bytes from lhr48s29-in-f14.1e100.net (142.250.200.14): icmp_seq=14 ttl=117 time=12.1 ms
^C
--- google.com ping statistics ---
14 packets transmitted, 5 received, 64% packet loss, time 13203ms
rtt min/avg/max/mdev = 9.163/16.080/35.886/9.959 ms
osboxes@kube-worker-vm2:~$ ping docker.io
PING docker.io (35.169.217.170) 56(84) bytes of data.