routing: T1237: Add new feature failover route

Failover route allows to install static routes to the kernel routing
table only if required target or gateway is alive
When target or gateway doesn't respond for ICMP/ARP checks this route
deleted from the routing table
Routes are marked as protocol 'failover' (rt_protos)

cat /etc/iproute2/rt_protos.d/failover.conf
111  failover

ip route add 203.0.113.1 metric 2 via 192.0.2.1 dev eth0 proto failover

$ sudo ip route show proto failover
203.0.113.1 via 192.0.2.1 dev eth0 metric 1

So we can safely flush such routes

1 files changed, 121 insertions, 0 deletions

diff --git a/src/conf_mode/protocols_failover.py b/src/conf_mode/protocols_failover.py
new file mode 100755
index 000000000..048ba7a89
--- /dev/null
+++ b/src/conf_mode/protocols_failover.py
@@ -0,0 +1,121 @@
+#!/usr/bin/env python3
+#
+# Copyright (C) 2022 VyOS maintainers and contributors
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 2 or later as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+import json
+
+from pathlib import Path
+
+from vyos.config import Config
+from vyos.configdict import dict_merge
+from vyos.template import render
+from vyos.util import call
+from vyos.xml import defaults
+from vyos import ConfigError
+from vyos import airbag
+
+airbag.enable()
+
+
+service_name = 'vyos-failover'
+service_conf = Path(f'/run/{service_name}.conf')
+systemd_service = '/etc/systemd/system/vyos-failover.service'
+rt_proto_failover = '/etc/iproute2/rt_protos.d/failover.conf'
+
+
+def get_config(config=None):
+    if config:
+        conf = config
+    else:
+        conf = Config()
+
+    base = ['protocols', 'failover']
+    failover = conf.get_config_dict(base, key_mangling=('-', '_'), get_first_key=True)
+
+    # Set default values only if we set config
+    if failover.get('route'):
+        for route, route_config in failover.get('route').items():
+            for next_hop, next_hop_config in route_config.get('next_hop').items():
+                default_values = defaults(base + ['route'])
+                failover['route'][route]['next_hop'][next_hop] = dict_merge(
+                    default_values['next_hop'], failover['route'][route]['next_hop'][next_hop])
+
+    return failover
+
+def verify(failover):
+    # bail out early - looks like removal from running config
+    if not failover:
+        return None
+
+    if 'route' not in failover:
+        raise ConfigError(f'Failover "route" is mandatory!')
+
+    for route, route_config in failover['route'].items():
+        if not route_config.get('next_hop'):
+            raise ConfigError(f'Next-hop for "{route}" is mandatory!')
+
+        for next_hop, next_hop_config in route_config.get('next_hop').items():
+            if 'interface' not in next_hop_config:
+                raise ConfigError(f'Interface for route "{route}" next-hop "{next_hop}" is mandatory!')
+
+            if not next_hop_config.get('check'):
+                raise ConfigError(f'Check target for next-hop "{next_hop}" is mandatory!')
+
+            if 'target' not in next_hop_config['check']:
+                raise ConfigError(f'Check target for next-hop "{next_hop}" is mandatory!')
+
+            check_type = next_hop_config['check']['type']
+            if check_type == 'tcp' and 'port' not in next_hop_config['check']:
+                raise ConfigError(f'Check port for next-hop "{next_hop}" and type TCP is mandatory!')
+
+    return None
+
+def generate(failover):
+    if not failover:
+        service_conf.unlink(missing_ok=True)
+        return None
+
+    # Add own rt_proto 'failover'
+    # Helps to detect all own routes 'proto failover'
+    with open(rt_proto_failover, 'w') as f:
+        f.write('111  failover\n')
+
+    # Write configuration file
+    conf_json = json.dumps(failover, indent=4)
+    service_conf.write_text(conf_json)
+    render(systemd_service, 'protocols/systemd_vyos_failover_service.j2', failover)
+
+    return None
+
+def apply(failover):
+    if not failover:
+        call(f'systemctl stop {service_name}.service')
+        call('ip route flush protocol failover')
+    else:
+        call('systemctl daemon-reload')
+        call(f'systemctl restart {service_name}.service')
+        call(f'ip route flush protocol failover')
+
+    return None
+
+if __name__ == '__main__':
+    try:
+        c = get_config()
+        verify(c)
+        generate(c)
+        apply(c)
+    except ConfigError as e:
+        print(e)
+        exit(1)