Merge pull request srl-labs#330 from vrnetlab/topomachine-keep-order

Add --keep-order to topomachine

Author: mzagozen

topology-machine/README.md

@@ -34,6 +34,15 @@ topomachine does not currently use any information from the low level topology
 will very likely result in changes to the majority of links in the topology as
 they will be re-assigned to new interfaces.
 
+The default behavior is to sort the routers and links and assign interfaces
+numbers to links in this sorted order. There is however an option called
+`--keep-order` that will take into account the order in which the *p2p* links
+and routers in *fullmeshes* are defined in the configuration file. This makes
+the interface assignment more stable when changing the topology. It also makes
+the assignment more natural, as we tend to list the important routers (like PE
+routers) in the topology first, followed by CPEs and the like. The interfaces on
+the devices listed first will be assigned lower numbers.
+
 topology machine is able to run the machines for you, i.e. execute docker run
 for the routers defined in the configuration file and start vr-xcon with the
 relevant arguments to complete the topology:

topology-machine/topomachine

@@ -10,13 +10,15 @@ import jinja2
 class VrTopo:
     """ vrnetlab topo builder
     """
-    def __init__(self, config):
-        self.routers = {}
+    def __init__(self, config, keep_order):
+        self.keep_order = keep_order
         self.links = []
         self.fullmeshes = {}
         self.hubs = {}
         if 'routers' in config:
             self.routers = config['routers']
+        else:
+            self.routers = {}
 
         # sanity checking - use a YANG model and pyang to validate input?
         for r, val in self.routers.items():
@@ -25,21 +27,41 @@ class VrTopo:
             if val['type'] not in ('dummy', 'xcon', 'bgp', 'xrv', 'xrv9k', 'vmx', 'sros', 'csr', 'nxos', 'nxos9kv', 'vqfx', 'vrp', 'veos', 'openwrt'):
                 raise ValueError("Unknown type %s for router %s" % (val['type'], r))
 
-        # expand p2p links
+        # preserve order of entries if keep_order is set
+        def maybe_sorted(d):
+            if keep_order:
+                return d
+            else:
+                return sorted(d)
+
         links = []
-        if 'p2p' in config:
-            for router in sorted(config['p2p']):
-                neighbors = config['p2p'][router]
-                for neighbor in neighbors:
-                    links.append({ 'left': { 'router': router }, 'right': {
-                        'router': neighbor }})
+
+        # expand p2p links
+        def p2p():
+            nonlocal links
+            if 'p2p' in config:
+                for router in maybe_sorted(config['p2p']):
+                    neighbors = config['p2p'][router]
+                    for neighbor in neighbors:
+                        links.append({ 'left': { 'router': router }, 'right': {
+                            'router': neighbor }})
 
         # expand fullmesh into links
-        if 'fullmeshes' in config:
-            for name in sorted(config['fullmeshes']):
-                val = config['fullmeshes'][name]
-                fmlinks = self.expand_fullmesh(val)
-                links.extend(fmlinks)
+        def fullmesh():
+            nonlocal links
+            if 'fullmeshes' in config:
+                for name in maybe_sorted(config['fullmeshes']):
+                    val = config['fullmeshes'][name]
+                    fmlinks = self.expand_fullmesh(val)
+                    links.extend(fmlinks)
+
+        # expand fullmeshes before p2p if keep_order is set and fullmeshes is defined before p2p
+        if keep_order and 'fullmeshes' in config and 'p2p' in config and tuple(config).index('fullmeshes') < tuple(config).index('p2p'):
+            fullmesh()
+            p2p()
+        else:
+            p2p()
+            fullmesh()
 
         self.links = self.assign_interfaces(links)
 
@@ -73,9 +95,8 @@ class VrTopo:
                 for num_id in val['interfaces']:
                     val['interfaces'][num_id] = self.intf_num_to_name(router, num_id)
 
-
-
-    def expand_fullmesh(self, routers):
+    @staticmethod
+    def expand_fullmesh(routers):
         """ Flatten a full-mesh into a list of links
 
             Links are considered bi-directional, so you will only see a link A->B
@@ -179,7 +200,7 @@ class VrTopo:
             }
 
         if output_format == 'json':
-            return json.dumps(output, sort_keys=True, indent=4)
+            return json.dumps(output, sort_keys=(not self.keep_order), indent=4)
         else:
             raise ValueError("Invalid output format")
 
@@ -299,6 +320,7 @@ if __name__ == '__main__':
     import argparse
     parser = argparse.ArgumentParser()
     parser.add_argument("--build", help="Build topology from config")
+    parser.add_argument("--keep-order", action="store_true", help="Keep topology order (routers, links, fullmeshes). Applies to --build only")
     parser.add_argument("--run", help="Run topology")
     parser.add_argument("--dry-run", action="store_true", default=False, help="Only print what would be performed during --run")
     parser.add_argument("--prefix", default='', help="docker container name prefix")
@@ -321,7 +343,7 @@ if __name__ == '__main__':
         config = json.loads(input_file.read(), object_pairs_hook=OrderedDict)
         input_file.close()
         try:
-            vt = VrTopo(config)
+            vt = VrTopo(config, args.keep_order)
         except Exception as exc:
             print("ERROR:", exc)
             sys.exit(1)