Pause autoinstall on network screen

autoinstall/user-data

@@ -1,14 +1,18 @@
 #cloud-config
 autoinstall:
   version: 1
+  interactive-sections:
+    - network
 
   # ── Locale & keyboard ──────────────────────────
   locale: en_IN.UTF-8
   keyboard:
     layout: us
 
-  # ── Network: DHCP on first ethernet ───────────
-  # Final network config is set by the web setup UI (browser on port 80)
+  # ── Network: stop on installer network screen ─
+  # Subiquity will show the network UI and use the values below as defaults.
+  # This lets the operator set the final static IP from the VM console before
+  # installation completes.
   network:
     network:
       version: 2

autoinstall/websetup/server.py

@@ -58,6 +58,19 @@ def validate_static_network(ip, prefix, gateway, dns):
         raise ValueError("CIDR prefix must be between 1 and 32")
     return str(prefix_int)
 
+def is_ip_in_use(ip):
+    """Best-effort conflict check before taking a static IP."""
+    try:
+        result = subprocess.run(
+            ["ping", "-c", "1", "-W", "1", ip],
+            stdout=subprocess.DEVNULL,
+            stderr=subprocess.DEVNULL,
+            check=False,
+        )
+        return result.returncode == 0
+    except Exception:
+        return False
+
 def apply_static_ip(iface, ip, prefix, gateway, dns):
     prefix = validate_static_network(ip, prefix, gateway, dns)
     config = f"""network:
@@ -270,6 +283,9 @@ HTML = r"""<!DOCTYPE html>
       </div>
 
       <div class="static-fields" id="static-fields">
+        <div class="alert alert-info">
+          We will ping the IP before applying it. If it replies, we will block the change to avoid taking an address that is already in use.
+        </div>
         <div class="ip-row">
           <div class="form-group">
             <label>IP Address</label>
@@ -437,7 +453,15 @@ function applyStaticIP() {
     dns:     document.getElementById('ip-dns').value,
   };
   fetch('/api/network', { method:'POST', headers:{'Content-Type':'application/json'}, body: JSON.stringify(body) })
-    .then(r=>r.json()).then(d=>{ if(!d.ok) alert('Network config failed: ' + d.error); });
+    .then(r=>r.json()).then(d=>{
+      if(!d.ok) {
+        alert('Network config failed: ' + d.error);
+        return;
+      }
+      if (d.warning) {
+        alert(d.warning);
+      }
+    });
 }
 
 // ── Tier ───────────────────────────────────────────────────
@@ -663,7 +687,20 @@ class Handler(BaseHTTPRequestHandler):
                 if body.get("mode") == "static":
                     ifaces = get_interfaces()
                     iface = ifaces[0] if ifaces else "eth0"
+                    validate_static_network(body["ip"], body["prefix"], body["gateway"], body["dns"])
+                    if is_ip_in_use(body["ip"]):
+                        self.send_json({
+                            "ok": False,
+                            "error": f"IP address {body['ip']} is already replying to ping. Choose a different address."
+                        }, 409)
+                        return
                     apply_static_ip(iface, body["ip"], body["prefix"], body["gateway"], body["dns"])
+                    self.send_json({
+                        "ok": True,
+                        "ip": get_ip(),
+                        "warning": "Ping check passed before applying the static IP. Note: a non-reply does not guarantee the address is unused if another host blocks ICMP."
+                    })
+                    return
                 self.send_json({"ok": True, "ip": get_ip()})
             except Exception as e:
                 self.send_json({"ok": False, "error": str(e)}, 500)