krelay is a drop-in replacement for kubectl port-forward with some enhanced features.

• Highlights
• Demo
• Installation
• Usage
• Flags
• How It Works

• Supports UDP port forwarding
• Supports simultaneous forwarding of data to multiple targets.
• Forwarding data to the given IP or hostname that is accessible within the kubernetes cluster
  • You could forward a local port to a port in the Service or a workload like Deployment or StatefulSet , and the forwarding session will not be interfered even if you perform rolling updates.
  • The hostname is resolved inside the cluster, so you don't need to change your local nameserver or modify the /etc/hosts .

$ cat 
>
 targets.txt 
<<
EOF

# Each line in the file represents a target, the syntax is the same as the command line.

# Empty line or line starts with '#' or '//' will be ignored.


# namespace of the object can be specified by the -n flag

-n kube-system svc/kube-dns 10053:53@udp


# The default namespace is used if no namespace is specified

svc/nginx 8080:80


host/redis.cn-north-1.cache.amazonaws.com 6379

EOF


$ kubectl relay -f targets.txt

wget https://raw.githubusercontent.com/knight42/krelay/main/manifests/rbac.yaml
#
 Edit rbac.yaml to update the user name

vim rbac.yaml
kubectl create -f rbac.yaml

git clone https://github.com/knight42/krelay
cd krelay
make krelay
cp krelay "$GOPATH/bin/kubectl-relay"
kubectl relay -V

#
 Listen on port 8080 locally, forwarding data to the port named "http" in the service

kubectl relay service/my-service 8080:http

#
 Listen on a random port locally, forwarding udp packets to port 53 in a pod selected by the deployment

kubectl relay -n kube-system deploy/kube-dns :53@udp

#
 Listen on port 5353 on all addresses, forwarding data to port 53 in the pod

kubectl relay --address 0.0.0.0 pod/my-pod 5353:53

#
 Listen on port 6379 locally, forwarding data to "redis.cn-north-1.cache.amazonaws.com:6379" from the cluster

kubectl relay host/redis.cn-north-1.cache.amazonaws.com 6379

#
 Listen on port 5000 and 6000 locally, forwarding data to "1.2.3.4:5000" and "1.2.3.4:6000" from the cluster

kubectl relay ip/1.2.3.4 5000@tcp 6000@udp

#
 Create the agent in the kube-public namespace, and forward local port 5000 to "1.2.3.4:5000"

kubectl relay --server.namespace kube-public ip/1.2.3.4 5000

krelay will install an agent(named krelay-server ) to the kubernetes cluster, and the agent will forward the traffic to the target ip/hostname.

If the target is an object in the cluster, like Deployment , StatefulSet , krelay will automatically select a pod it managed like kubectl port-forward does. After that krelay will tell the destination IP(i.e. the pod's IP) and the destination port to the agent by sending a special Header first, and then the data will be forwarded to the agent and sent to the target address.

Specifically, if the target is a Service , krelay will try to determine the destination address automatically:

• If the Service has a clusterIP, then the clusterIP is used as the destination IP.
• If the type of Service is ExternalName , then the external name is used as the destination address.
• If none of the above scenario is met, then krelay will choose a pod selected by this Service .

The Header looks like this:

• Version : This field is preserved for future extension, and it is not in-use now.
• Header Length : The total length of the Header in bytes.
• Request ID : The ID of the request.
• Protocol : The protocol of the request, 0 stands for TCP and 1 stands for UDP.
• Destination Port : The destination port of the request.
• Address Type : The type of the destination address, 0 stands for IP and 1 stands for hostname.
• Address : The destination address of the request:
  • 4 bytes for IPv4 address
  • 16 bytes for IPv6 address
  • Variable bytes for hostname