instruction: Create a comprehensive Dockerfile for cluster applications with best practices
output: ```dockerfile
  from the Kubernetes container image registry,
  registry.k8s.io. If you want to deploy a highly-available cluster where the hosts do not have
  access to pull images, this is possible. You must ensure by some other means that the correct
  container images are already available on the relevant hosts.Command line interfaceTo manage Kubernetes once your cluster is set up, you should
  install kubectl on your PC. It is also useful
  to install the kubectl tool on each control plane node, as this can be
  helpful for troubleshooting.First steps for both methodsCreate load balancer for kube-apiserverNote:There are many configurations for load balancers. The following example is only one
  option. Your cluster requirements may need a different configuration.Create a kube-apiserver load balancer with a name that resolves to DNS.In a cloud environment you should place your control plane nodes behind a TCP
  forwarding load balancer. This load balancer distributes traffic to all
  healthy control plane nodes in its target list. The health check for
  an apiserver is a TCP check on the port the kube-apiserver listens on
  (default value :6443).It is not recommended to use an IP address directly in a cloud environment.The load balancer must be able to communicate with all control plane nodes
  on the apiserver port. It must also allow incoming traffic on its
  listening port.Make sure the address of the load balancer always matches
  the address of kubeadm's ControlPlaneEndpoint.Read the Options for Software Load Balancing
  guide for more details.Add the first control plane node to the load balancer, and test the
  connection:nc -zv -w 2 <LOAD_BALANCER_IP> <PORT>
  A connection refused error is expected because the API server is not yet
  running. A timeout, however, means the load balancer cannot communicate
  with the control plane node. If a timeout occurs, reconfigure the load
  balancer to communicate with the control plane node.Add the remaining control plane nodes to the load balancer target group.Stacked control plane and etcd nodesSteps for the first control plane nodeInitialize the control plane:sudo kubeadm init --control-plane-endpoint "LOAD_BALANCER_DNS:LOAD_BALANCER_PORT" --upload-certs
  You can use the --kubernetes-version flag to set the Kubernetes version to use.
  It is recommended that the versions of kubeadm, kubelet, kubectl and Kubernetes match.The --control-plane-endpoint flag should be set to the address or DNS and port of the load balancer.The --upload-certs flag is used to upload the certificates that should be shared
  across all the control-plane instances to the cluster. If instead, you prefer to copy certs across
  control-plane nodes manually or using automation tools, please remove this flag and refer to Manual
  certificate distribution section below.Note:The kubeadm init flags --config and --certificate-key cannot be mixed, therefore if you want
  to use the kubeadm configuration
  you must add the certificateKey field in the appropriate config locations
  (under InitConfiguration and JoinConfiguration: controlPlane).Note:Some CNI network plugins require additional configuration, for example specifying the pod IP CIDR, while others do not.
  See the CNI network documentation.
  To add a pod CIDR pass the flag --pod-network-cidr, or if you are using a kubeadm configuration file
  set the podSubnet field under the networking object of ClusterConfiguration.The output looks similar to:...
  You can now join any number of control-plane node by running the following command on each as a root:
   kubeadm join 192.168.0.200:6443 --token 9vr73a.a8uxyaju799qwdjv --discovery-token-ca-cert-hash sha256:7c2e69131a36ae2a042a339b33381c6d0d43887e2de83720eff5359e26aec866 --control-plane --certificate-key f8902e114ef118304e561c3ecd4d0b543adc226b7a07f675f56564185ffe0c07
  
  Please note that the certificate-key gives access to cluster sensitive data, keep it secret!
  As a safeguard, uploaded-certs will be deleted in two hours; If necessary, you can use kubeadm init phase upload-certs to reload certs afterward.
  
  Then you can join any number of worker nodes by running the following on each as root:
   kubeadm join 192.168.0.200:6443 --token 9vr73a.a8uxyaju799qwdjv --discovery-token-ca-cert-hash sha256:7c2e69131a36ae2a042a339b33381c6d0d43887e2de83720eff5359e26aec866
  Copy this output to a text file. You will need it later to join control plane and worker nodes to
  the cluster.When --upload-certs is used with kubeadm init, the certificates of the primary control plane
  are encrypted and uploaded in the kubeadm-certs Secret.To re-upload the certificates and generate a new decryption key, use the following command on a
  control plane
  node that is already joined to the cluster:sudo kubeadm init phase upload-certs --upload-certs
  You can also specify a custom --certificate-key during init that can later be used by join.
  To generate such a key you can use the following command:kubeadm certs certificate-key
  The certificate key is a hex encoded string that is an AES key of size 32 bytes.Note:The kubeadm-certs Secret and the decryption key expire after two hours.Caution:As stated in the command output, the certificate key gives access to cluster sensitive data, keep it secret!Apply the CNI plugin of your choice:
  Follow these instructions
  to install the CNI provider. Make sure the configuration corresponds to the Pod CIDR specified in the
  kubeadm configuration file (if applicable).Note:You must pick a network plugin that suits your use case and deploy it before you move on to next step.
  If you don't do this, you will not be able to launch your cluster properly.Type the following and watch the pods of the control plane components get started:kubectl get pod -n kube-system -w
  Steps for the rest of the control plane nodesFor each additional control plane node you should:Execute the join command that was previously given to you by the kubeadm init output on the first node.
  It should look something like this:sudo kubeadm join 192.168.0.200:6443 --token 9vr73a.a8uxyaju799qwdjv --discovery-token-ca-cert-hash sha256:7c2e69131a36ae2a042a339b33381c6d0d43887e2de83720eff5359e26aec866 --control-plane --certificate-key f8902e114ef118304e561c3ecd4d0b543adc226b7a07f675f56564185ffe0c07
  The --control-plane flag tells kubeadm join to create a new control plane.The --certificate-key ... will cause the control plane certificates to be downloaded
  ```