Add X-mode for debugging minimal systens (#51)

Signed-off-by: Andrei Kvapil <kvapss@gmail.com>

Author: kvaps

README.md

@@ -28,6 +28,9 @@ sudo mv ./kubectl-node_shell /usr/local/bin/kubectl-node_shell
 # Get standard bash shell
 kubectl node-shell <node>
 
+# Use X-mode (mount /host, and do not enter host namespace)
+kubectl node-shell -x <node>
+
 # Execute custom command
 kubectl node-shell <node> -- echo 123
 
@@ -38,4 +41,38 @@ cat /etc/passwd | kubectl node-shell <node> -- sh -c 'cat > /tmp/passwd'
 kubectl node-shell <node> -- sh -c 'cat /tmp/passwd; rm -f /tmp/passwd'
 ```
 
+## X-mode
+
+X-mode can be useful for debugging minimal systems that do not have a built-in shell (eg. Talos).  
+Here's an example of how you can debug the network for a rootless kube-apiserver container without a filesystem:
+
+```bash
+kubectl node-shell -x <node>
+
+# Download crictl
+wget https://github.com/kubernetes-sigs/cri-tools/releases/download/v1.28.0/crictl-v1.28.0-linux-amd64.tar.gz -O- | \
+  tar -xzf- -C /usr/local/bin/
+
+# Setup CRI endpoint
+export CONTAINER_RUNTIME_ENDPOINT=unix:///host/run/containerd/containerd.sock
+
+# Find your container
+crictl ps | grep kube-apiserver
+#3ff4626a9f10e       e7972205b6614       6 hours ago         Running             kube-apiserver         0                   215107b47bd7e       kube-apiserver-talos-rzq-nkg
+
+# Find pid of the container
+crictl inspect 3ff4626a9f10e | grep pid
+#    "pid": 2152,
+#            "pid": 1
+#            "type": "pid"
+#                "getpid",
+#                "getppid",
+#                "pidfd_open",
+#                "pidfd_send_signal",
+#                "waitpid",
+
+# Go to network namespace of the pid, but keep mount namespace of the debug container
+nsenter -t 2152 -n
+```
+
 *You need to be able to start privileged containers for that.*

kubectl-node_shell

@@ -2,13 +2,16 @@
 set -e
 
 kubectl=kubectl
-version=1.7.0
+version=1.8.0
 generator=""
 node=""
 nodefaultctx=0
 nodefaultns=0
 container_cpu="${KUBECTL_NODE_SHELL_POD_CPU:-100m}"
 container_memory="${KUBECTL_NODE_SHELL_POD_MEMORY:-256Mi}"
+volumes="[]"
+volume_mounts="[]"
+x_mode=0
 labels="${KUBECTL_NODE_SHELL_LABELS}"
 
 if [ -t 0 ]; then
@@ -55,6 +58,12 @@ while [ $# -gt 0 ]; do
     kubectl="$kubectl --namespace=${key##*=}"
     shift
     ;;
+  -x)
+    x_mode=1
+    volumes='[{"hostPath":{"path":"/","type":""},"name":"host-root"}]'
+    volume_mounts='[{"mountPath":"/host","name":"host-root"}]'
+    shift
+    ;;
   --)
     shift
     break
@@ -106,16 +115,26 @@ fi
 
 # Build the container command
 if [ $# -gt 0 ]; then
-  cmd="[ $cmd_start $cmd_arg_prefix"
+  if [ "$x_mode" -eq 1 ]; then
+    cmd='['
+  else
+    cmd="[ $cmd_start $cmd_arg_prefix,"
+  fi
+  c=""
   while [ $# -gt 0 ]; do
-    cmd="$cmd, \"$(echo "$1" | \
+    cmd="${cmd}${c} \"$(echo "$1" | \
       awk '{gsub(/["\\]/,"\\\\&");gsub(/\x1b/,"\\u001b");printf "%s",last;last=$0"\\n"} END{print $0}' \
     )\""
+    c=,
     shift
   done
   cmd="$cmd ]"
 else
-  cmd="[ $cmd_start $cmd_default ]"
+  if [ "$x_mode" = 1 ]; then
+    cmd='null'
+  else
+    cmd="[ $cmd_start $cmd_default ]"
+  fi
 fi
 
 overrides="$(
@@ -137,13 +156,15 @@ cat <<EOT
         "resources": {
           "limits":   { "cpu": "${container_cpu}", "memory": "${container_memory}" },
           "requests": { "cpu": "${container_cpu}", "memory": "${container_memory}" }
-        }
+        },
+        "volumeMounts": $volume_mounts
       }
     ],
     "tolerations": [
       { "key": "CriticalAddonsOnly", "operator": "Exists" },
       { "effect": "NoExecute",       "operator": "Exists" }
-    ]
+    ],
+    "volumes": $volumes
   }
 }
 EOT