feat: parallelize worker rebuilds with retry and timeout

nixos/kubeadm/README.md

@@ -105,6 +105,12 @@ $EDITOR ./scripts/inventory.env
 ./scripts/rebuild-and-bootstrap.sh
 ```
 
+Optional tuning env vars:
+
+```bash
+WORKER_PARALLELISM=2 REBUILD_TIMEOUT=45m REBUILD_RETRIES=2 ./scripts/rebuild-and-bootstrap.sh
+```
+
 3. If you only want to reset Kubernetes state on existing VMs:
 
 ```bash

nixos/kubeadm/scripts/rebuild-and-bootstrap.sh

@@ -18,6 +18,9 @@ SSH_USER="${SSH_USER:-micqdf}"
 SSH_KEY_PATH="${SSH_KEY_PATH:-$HOME/.ssh/id_ed25519}"
 SSH_OPTS="${SSH_OPTS:--o BatchMode=yes -o IdentitiesOnly=yes -o StrictHostKeyChecking=accept-new -i $SSH_KEY_PATH}"
 SSH_USER_CANDIDATES="${SSH_USER_CANDIDATES:-root $SSH_USER}"
+REBUILD_TIMEOUT="${REBUILD_TIMEOUT:-45m}"
+REBUILD_RETRIES="${REBUILD_RETRIES:-2}"
+WORKER_PARALLELISM="${WORKER_PARALLELISM:-2}"
 
 declare -A NODE_IPS=()
 declare -a CP_NAMES=()
@@ -126,12 +129,36 @@ rebuild_node() {
   local node_ip="$2"
 
   echo "==> Rebuilding $node_name on $node_ip"
-  nixos-rebuild switch \
+  timeout "$REBUILD_TIMEOUT" nixos-rebuild switch \
     --flake "$FLAKE_DIR#$node_name" \
     --target-host "$ACTIVE_SSH_USER@$node_ip" \
     --use-remote-sudo
 }
 
+rebuild_node_with_retry() {
+  local node_name="$1"
+  local node_ip="$2"
+  local attempt=1
+  local max_attempts=$((REBUILD_RETRIES + 1))
+
+  while [ "$attempt" -le "$max_attempts" ]; do
+    echo "==> Rebuild attempt $attempt/$max_attempts for $node_name"
+    if rebuild_node "$node_name" "$node_ip"; then
+      return 0
+    fi
+
+    if [ "$attempt" -lt "$max_attempts" ]; then
+      echo "==> Rebuild failed for $node_name, retrying after 20s"
+      sleep 20
+    fi
+
+    attempt=$((attempt + 1))
+  done
+
+  echo "==> Rebuild failed permanently for $node_name"
+  return 1
+}
+
 prepare_remote_nix_trust() {
   local node_ip="$1"
   echo "==> Ensuring nix trusted-users on $node_ip"
@@ -164,15 +191,42 @@ detect_ssh_user "$PRIMARY_CP_IP"
 for node in "${CP_NAMES[@]}"; do
   prepare_remote_nix_trust "${NODE_IPS[$node]}"
   prepare_remote_space "${NODE_IPS[$node]}"
-  rebuild_node "$node" "${NODE_IPS[$node]}"
+  rebuild_node_with_retry "$node" "${NODE_IPS[$node]}"
 done
 
+worker_failures=0
 for node in "${WK_NAMES[@]}"; do
   prepare_remote_nix_trust "${NODE_IPS[$node]}"
   prepare_remote_space "${NODE_IPS[$node]}"
-  rebuild_node "$node" "${NODE_IPS[$node]}"
 done
 
+active_jobs=0
+for node in "${WK_NAMES[@]}"; do
+  (
+    rebuild_node_with_retry "$node" "${NODE_IPS[$node]}"
+  ) &
+
+  active_jobs=$((active_jobs + 1))
+  if [ "$active_jobs" -ge "$WORKER_PARALLELISM" ]; then
+    if ! wait -n; then
+      worker_failures=$((worker_failures + 1))
+    fi
+    active_jobs=$((active_jobs - 1))
+  fi
+done
+
+while [ "$active_jobs" -gt 0 ]; do
+  if ! wait -n; then
+    worker_failures=$((worker_failures + 1))
+  fi
+  active_jobs=$((active_jobs - 1))
+done
+
+if [ "$worker_failures" -gt 0 ]; then
+  echo "==> $worker_failures worker rebuild job(s) failed"
+  exit 1
+fi
+
 echo "==> Initializing control plane on $PRIMARY_CONTROL_PLANE"
 if cluster_ready; then
   echo "==> Existing cluster detected on $PRIMARY_CONTROL_PLANE; skipping kubeadm init"