diff --git a/apt/APT_Profile.pm.in b/apt/APT_Profile.pm.in
index f9985cfdaeb66f3f3386fabb85ad9c1253699033..12527a806d9340e83f921c0a5a65db91be121d44 100644
--- a/apt/APT_Profile.pm.in
+++ b/apt/APT_Profile.pm.in
@@ -762,7 +762,7 @@ sub ConvertDiskImages($)
 }
 
 # Total nonsense, to be thrown away.
-sub CheckImageConstraints($$$)
+sub CheckNodeConstraints($$$)
 {
     my ($self, $iscloudlab, $pmsg) = @_;
     my $cloudwww = "www.utah.cloudlab.us";
@@ -775,12 +775,36 @@ sub CheckImageConstraints($$$)
     }
     foreach my $ref (GeniXML::FindNodes("n:node", $rspec)->get_nodelist()) {
 	my $client_id = GetVirtualId($ref);
+	my $virtualization_type = GeniXML::GetVirtualizationSubtype($ref);
+
+	if (defined($virtualization_type) && $iscloudlab &&
+	    $virtualization_type eq "emulab-xen") {
+	    $$pmsg = "Node '$client_id' is a XEN VM, which is ".
+		"not supported on the Cloudlab cluster";
+	    return -1;
+	}
 	my $diskref   = GeniXML::GetDiskImage($ref);
 	next
 	    if (!defined($diskref));
 	my $image_url = GeniXML::GetText("url", $diskref);
+	my $image_urn = GeniXML::GetText("name", $diskref);
 	next
-	    if (!defined($image_url));
+	    if (!(defined($image_url) || defined($image_urn)));
+
+	if (defined($image_urn)) {
+	    if ($iscloudlab && $image_urn !~ /ARM/) {
+		$$pmsg = "Node '$client_id' disk_image will not run ".
+		    "on the Cloudlab cluster";
+		return -1;
+	    }
+	    elsif (!$iscloudlab && $image_urn =~ /ARM/) {
+		$$pmsg = "Node '$client_id' disk_image will only run ".
+		    "on the Cloudlab cluster";
+		return -1;
+	    }
+	}
+	next if
+	    (!defined($image_url));
 
 	# Get the hostname for the image URL.
 	my $uri = URI->new($image_url);
diff --git a/apt/create_instance.in b/apt/create_instance.in
index c353571814d46f7bbc7cc8db7c87bf28a5a4ad02..550244159133a56086e14a3cd6d102f351063874 100755
--- a/apt/create_instance.in
+++ b/apt/create_instance.in
@@ -311,7 +311,7 @@ if (APT_Profile::CheckDatasets($rspecstr, $profile_object->pid(), \$errmsg)) {
 my $iscloudlab =
     ($CMURN eq "urn:publicid:IDN+utah.cloudlab.us+authority+cm" ? 1 : 0);
 
-if ($profile_object->CheckImageConstraints($iscloudlab, \$errmsg)) {
+if ($profile_object->CheckNodeConstraints($iscloudlab, \$errmsg)) {
     UserError($errmsg);
 }
 
@@ -522,6 +522,7 @@ print STDERR "Email:   $user_email" . (!$localuser ? " (guest)" : "") . "\n";
 print STDERR "Profile: " . $profile_object->name() . ":${version}\n";
 print STDERR "Slice:   $slice_urn\n";
 print STDERR "Server:  $SERVER_NAME\n";
+print STDERR "Cluster: $CMURN\n";
 print STDERR "\n";
 print STDERR "$rspecstr\n";
 
diff --git a/www/aptui/instance_defs.php b/www/aptui/instance_defs.php
index 0744ca1d44efeddccf29e053bf83c170916f1b34..70190b7d96ec93c5c313d2e616b89599df05a9af 100644
--- a/www/aptui/instance_defs.php
+++ b/www/aptui/instance_defs.php
@@ -24,7 +24,7 @@
 #
 
 $am_array = array('Utah APT' =>
-		     "urn:publicid:IDN+apt.emulab.net+authority+cm",
+		  "urn:publicid:IDN+apt.emulab.net+authority+cm",
 		  'Utah Cloudlab' =>
 		     "urn:publicid:IDN+utah.cloudlab.us+authority+cm",
 		  'Utah DDC' =>
@@ -32,6 +32,13 @@ $am_array = array('Utah APT' =>
 		  'Utah PG'  =>
 		     "urn:publicid:IDN+emulab.net+authority+cm");
 
+if ($ISCLOUD) {
+    $DEFAULT_AGGREGATE = "Utah Cloudlab";
+}
+else {
+    $DEFAULT_AGGREGATE = "Utah APT";
+}
+
 class Instance
 {
     var	$instance;
diff --git a/www/aptui/instantiate.ajax b/www/aptui/instantiate.ajax
index 254a563f71198dd9e6baf38c712d708b6da2f65f..1a5f62fcf22df12bdfad78779aff8f111fbf3c4e 100644
--- a/www/aptui/instantiate.ajax
+++ b/www/aptui/instantiate.ajax
@@ -25,6 +25,7 @@ chdir("..");
 include_once("webtask.php");
 chdir("apt");
 include_once("profile_defs.php");
+include_once("instance_defs.php");
 
 #
 # Return info about specific profile.
@@ -33,6 +34,7 @@ function Do_GetProfile()
 {
     global $this_user;
     global $ajax_args;
+    global $DEFAULT_AGGREGATE;
     
     if (!isset($ajax_args["uuid"])) {
 	SPITAJAX_ERROR(1, "Missing profile uuid");
@@ -48,12 +50,19 @@ function Do_GetProfile()
 	SPITAJAX_ERROR(1, "No such profile $uuid");
 	return;
     }
+    $amdefault = $DEFAULT_AGGREGATE;
+    # Temporary override until constraint system in place.
+    if ($profile->BestAggregate()) {
+	$amdefault = $profile->BestAggregate();
+    }
+    
     #
     # Knowing the UUID means the user can instantiate it,
     # so no permission checks on the profile. 
     #
     SPITAJAX_RESPONSE(array('rspec'       => $profile->rspec(),
-			    'name'        => $profile->name()));
+			    'name'        => $profile->name(),
+			    'amdefault'   => $amdefault));
 }
 # Local Variables:
 # mode:php
diff --git a/www/aptui/instantiate.php b/www/aptui/instantiate.php
index a80c0d0f37e0b8aa0937ab5a603a2f89721bb8b1..f822625ac6534659c68c844408aa023bdbb84efc 100755
--- a/www/aptui/instantiate.php
+++ b/www/aptui/instantiate.php
@@ -469,12 +469,8 @@ if (!isset($create)) {
     $defaults["email"]    = "";
     $defaults["sshkey"]   = "";
     $defaults["profile"]  = (isset($profile) ? $profile : $profile_default);
-    if ($ISCLOUD) {
-	$defaults["where"]    = 'Utah APT';
-    }
-    else {
-	$defaults["where"]    = 'Utah APT';
-    }
+    $defaults["where"]    = $DEFAULT_AGGREGATE;
+
     # 
     # Look for current user or cookie that tells us who the user is. 
     #
diff --git a/www/aptui/js/instantiate.js b/www/aptui/js/instantiate.js
index 8762ea04623732cc66d07ab78368ea5d86c501cf..15c0cb62598f98694012f4616e6c5b3bdeb2a5c0 100644
--- a/www/aptui/js/instantiate.js
+++ b/www/aptui/js/instantiate.js
@@ -8,6 +8,7 @@ function (_, sup, aboutaptString, aboutcloudString)
     'use strict';
 
     var ajaxurl;
+    var amdefault;
 
     function initialize()
     {
@@ -29,7 +30,7 @@ function (_, sup, aboutaptString, aboutcloudString)
 	    $('#verify_modal').modal('show');
 	}
         $('#quickvm_topomodal').on('shown.bs.modal', function() {
-            ShowProfileList($('.current'))
+            ShowProfileSelection($('.current'))
         });
 
 	$('button#reset-form').click(function (event) {
@@ -42,12 +43,11 @@ function (_, sup, aboutaptString, aboutcloudString)
 	});
 	$('li.profile-item').click(function (event) {
 	    event.preventDefault();
-	    ShowProfileList(event.target);
+	    ShowProfileSelection(event.target);
 	});
 	$('button#showtopo_select').click(function (event) {
 	    event.preventDefault();
-	    UpdateProfileSelection($('.selected'));
-	    ShowProfileList($('.selected'));
+	    ChangeProfileSelection($('.selected'));
 	    $('#quickvm_topomodal').modal('hide');
 	});
 	$('#instantiate_submit').click(function (event) {
@@ -55,52 +55,72 @@ function (_, sup, aboutaptString, aboutcloudString)
 	    return true;
 	});
 	var startProfile = $('#profile_name li[value = ' + window.PROFILE + ']')
-        UpdateProfileSelection(startProfile);
-	ShowProfileList(startProfile, true);
+        ChangeProfileSelection(startProfile);
 	_.delay(function () {$('.dropdown-toggle').dropdown();}, 500);
     }
 
     function resetForm($form) {
 	$form.find('input:text, input:password, select, textarea').val('');
     }
-    
-    function UpdateProfileSelection(selectedElement)
-    {
-	var profile_name = $(selectedElement).text();
-	var profile_value = $(selectedElement).attr('value');
-	$('#selected_profile').attr('value', profile_value);
-	$('#selected_profile_text').html("" + profile_name);
 
-	if (!$(selectedElement).hasClass('current')) {
+    function ShowProfileSelection(selectedElement) {
+	if (!$(selectedElement).hasClass('selected')) {
 	    $('#profile_name li').each(function() {
-		$(this).removeClass('current');
+		$(this).removeClass('selected');
 	    });
-	    $(selectedElement).addClass('current');
+	    $(selectedElement).addClass('selected');
 	}
+	
+	var continuation = function(rspec, description, name, amdefault) {
+	    $('#showtopo_title').html("<h3>" + name + "</h3>");
+	    $('#showtopo_description').html(description);
+	    sup.maketopmap('#showtopo_div', rspec, null);
+	};
+	GetProfile($(selectedElement).attr('value'), continuation);
     }
-
-    function ShowProfileList(selectedElement, justTitle)
-    {
-	var profile = $(selectedElement).attr('value');
-
-	if (!$(selectedElement).hasClass('selected')) {
+    
+    function ChangeProfileSelection(selectedElement) {
+	if (!$(selectedElement).hasClass('current')) {
 	    $('#profile_name li').each(function() {
-		$(this).removeClass('selected');
+		$(this).removeClass('current');
 	    });
-	    $(selectedElement).addClass('selected');
+	    $(selectedElement).addClass('current');
 	}
 
+	var profile_name = $(selectedElement).text();
+	var profile_value = $(selectedElement).attr('value');
+	$('#selected_profile').attr('value', profile_value);
+	$('#selected_profile_text').html("" + profile_name);
+	
+	var continuation = function(rspec, description, name, amdefault) {
+	    $('#showtopo_title').html("<h3>" + name + "</h3>");
+	    $('#showtopo_description').html(description);
+	    $('#selected_profile_description').html(description);
+
+	    // Set the default aggregate.
+	    if ($('#profile_where').length) {
+		// Deselect current option.
+		$('#profile_where option').prop("selected", false);
+		// Find and select new option.
+		$('#profile_where option')
+		    .filter('[value="'+ amdefault + '"]')
+                    .prop('selected', true);		
+	    }
+	};
+	GetProfile($(selectedElement).attr('value'), continuation);
+    }
+    
+    function GetProfile(profile, continuation) {
 	var callback = function(json) {
 	    if (json.code) {
 		alert("Could not get profile: " + json.value);
 		return;
 	    }
+	    console.info(json);
 	    
 	    var xmlDoc = $.parseXML(json.value.rspec);
 	    var xml    = $(xmlDoc);
     
-	    $('#showtopo_title').html("<h3>" + json.value.name + "</h3>");
-
 	    /*
 	     * We now use the desciption from inside the rspec, unless there
 	     * is none, in which case look to see if the we got one in the
@@ -117,18 +137,13 @@ function (_, sup, aboutaptString, aboutcloudString)
 	    if (!description || description == "") {
 		description = "Hmm, no description for this profile";
 	    }
-	    $('#showtopo_description').html(description);
-	    $('#selected_profile_description').html(description);
-
-	    if (! justTitle) {
-		sup.maketopmap('#showtopo_div', json.value.rspec, null);
-	    }
+	    continuation(json.value.rspec, description,
+			 json.value.name, json.value.amdefault);
 	}
 	var $xmlthing = sup.CallServerMethod(ajaxurl,
 					     "instantiate", "GetProfile",
 					     {"uuid" : profile});
 	$xmlthing.done(callback);
     }
-
     $(document).ready(initialize);
 });
diff --git a/www/aptui/js/manage_profile.js b/www/aptui/js/manage_profile.js
index 1bdb173746ac9283638bb488aaa0e056ba5a8941..4ec0466122af28c4b5c2f33b47fb0839ab17df0b 100644
--- a/www/aptui/js/manage_profile.js
+++ b/www/aptui/js/manage_profile.js
@@ -106,7 +106,8 @@ function (_, sup, filesize, JacksEditor, ShowImagingModal, moment,
     	var guest_html = guestInstTemplate({});
 	$('#guest_div').html(guest_html);
 	$('#publish_div').html(publishString);
-    	var instantiate_html = InstTemplate({ amlist: amlist });
+    	var instantiate_html = InstTemplate({ amlist: amlist,
+					      amdefault: window.AMDEFAULT});
 	$('#instantiate_div').html(instantiate_html);
     	var rspectext_html = rspectextTemplate({});
 	$('#rspectext_div').html(rspectext_html);
diff --git a/www/aptui/manage_profile.ajax b/www/aptui/manage_profile.ajax
index 58c1734b732684215b87a9fb3f8776c26c2cd57b..2cbc4ea549f3f0dd907221700bcce3cb4104f368 100644
--- a/www/aptui/manage_profile.ajax
+++ b/www/aptui/manage_profile.ajax
@@ -286,7 +286,7 @@ function Do_GuestInstantiate()
 #
 function Do_Instantiate()
 {
-    global $this_user, $am_array;
+    global $this_user, $am_array, $DEFAULT_AGGREGATE;
     global $ajax_args;
     
     $this_idx = $this_user->uid_idx();
@@ -321,6 +321,14 @@ function Do_Instantiate()
 	    return;
 	}
     }
+    else {
+	# Temporary until constraint system in place.
+	$best = $profile->BestAggregate();
+	if (!$best) {
+	    $best = $DEFAULT_AGGREGATE;
+	}
+	$opts = "-a " . $am_array[$best];
+    }
 
     #
     # Invoke the backend.
diff --git a/www/aptui/manage_profile.php b/www/aptui/manage_profile.php
index 1f01c8f708825b4ca08b44d2e876de0047661c90..a72ff379f73f47a724b6a90211af3294e32e04d3 100644
--- a/www/aptui/manage_profile.php
+++ b/www/aptui/manage_profile.php
@@ -56,7 +56,7 @@ $optargs = OptionalPageArguments("create",      PAGEARG_STRING,
 #
 function SPITFORM($formfields, $errors)
 {
-    global $this_user, $projlist, $action, $profile;
+    global $this_user, $projlist, $action, $profile, $DEFAULT_AGGREGATE;
     global $notifyupdate, $notifyclone, $snapuuid, $am_array;
     $viewing    = 0;
     $candelete  = 0;
@@ -104,10 +104,16 @@ function SPITFORM($formfields, $errors)
     echo "</script>\n";
 
     $amlist = array();
+    $amdefault = "";
     if ($viewing && (ISADMIN() || STUDLY())) {
  	while (list($am) = each($am_array)) {
 	    $amlist[] = $am;
 	}
+	$amdefault = $DEFAULT_AGGREGATE;
+	# Temporary override until constraint system in place.
+	if ($profile->BestAggregate()) {
+	    $amdefault = $profile->BestAggregate();
+	}
     }
     echo "<script type='text/plain' id='amlist-json'>\n";
     echo htmlentities(json_encode($amlist));
@@ -150,6 +156,7 @@ function SPITFORM($formfields, $errors)
     echo "    window.HISTORY  = $history;\n";
     echo "    window.ACTIVITY = $activity;\n";
     echo "    window.TITLE    = '$title';\n";
+    echo "    window.AMDEFAULT= '$amdefault';\n";
     echo "    window.BUTTONLABEL = '$button_label';\n";
     if (isset($snapuuid)) {
 	echo "    window.SNAPUUID = '$snapuuid';\n";
diff --git a/www/aptui/profile_defs.php b/www/aptui/profile_defs.php
index df13d4fd3ce04086baf4b78ec67d48f3eeea5e6a..b48b8322163193dd3dfe8c860b93208fb8ce8c72 100644
--- a/www/aptui/profile_defs.php
+++ b/www/aptui/profile_defs.php
@@ -389,5 +389,47 @@ class Profile
     function CanView($user) {
 	return $this->CanInstantiate($user);
     }
+
+    function BestAggregate() {
+	$parsed_xml = simplexml_load_string($this->rspec());
+
+	foreach ($parsed_xml->node as $node) {
+	    # No XEN VMs on Cloudlab yet.
+	    if ($node->sliver_type &&
+		$node->sliver_type["name"] &&
+		$node->sliver_type["name"] == "emulab-xen") {
+		return "Utah APT";
+	    }
+	    # Check URL
+	    if (! ($node->sliver_type &&
+		   $node->sliver_type->disk_image &&
+		   ($node->sliver_type->disk_image["url"] ||
+		    $node->sliver_type->disk_image["name"]))) {
+		continue;
+	    }
+	    if ($node->sliver_type->disk_image["name"]) {
+		$name = $node->sliver_type->disk_image["name"];
+		#
+		# The only image that runs on Cloudlab is UBUNTU14-64-ARM
+		#
+		if (preg_match("/ARM/", $name)) {
+		    return "Utah Cloudlab";
+		}
+		return "Utah APT";
+	    }
+	    else {
+		$url = $node->sliver_type->disk_image["url"];
+		if (preg_match("/utah\.cloudlab\.us/", $url)) {
+		    return "Utah Cloudlab";
+		}
+		if (preg_match("/emulab\.net/", $url) ||
+		    preg_match("/geniracks\.net/", $url) ||
+		    preg_match("/instageni/", $url)) {
+		    return "Utah APT";
+		}
+	    }
+	}
+	return null;
+    }
 }
 ?>
diff --git a/www/aptui/template/instantiate-modal.html b/www/aptui/template/instantiate-modal.html
index 4b1a6fab45d588a170dd1eaf7282d9f3f9c8a6e1..0ccc022ad59bd92d75d384cfd7a95b797ef4159c 100644
--- a/www/aptui/template/instantiate-modal.html
+++ b/www/aptui/template/instantiate-modal.html
@@ -9,7 +9,12 @@
 	  Please select an AM<br>
 	  <select id='instantiate_where'>
 	    <% _.each(amlist, function(name) { %>
-	    <option value='<%= name %>'><%= name %></option>
+	    <option
+	       <% if (name == amdefault) { %>
+	           selected
+	       <% } %>
+	       value='<%= name %>'><%= name %>
+	    </option>
 	    <% }); %>
 	  </select>
 	  <br><br>