Debug and logging

Logging

A simple way to set up stderr logging:

# to start logging on the DB init
ndb = NDB(log='on')

# ... or to start it in run time
ndb.log('on')

# ... the same as above, another syntax
ndb.log.on

# ... turn logging off
ndb.log('off')

# ... or
ndb.log.off

It is possible also to set up logging to a file or to a syslog server:

#
ndb.log('file_name.log')

#
ndb.log('syslog://server:port')

Fetching DB data

By default, NDB starts with an in-memory SQLite3 database. In order to perform post mortem analysis it may be more useful to start the DB with a file DB or a PostgreSQL as the backend.

See more: Database

RTNL events

All the loaded RTNL events may be stored in the DB. To turn that feature on, one should start NDB with the debug option:

ndb = NDB(debug=True)

The events may be downloaded later, e.g. before exit, with schema.export_debug():

with NDB(log='on', debug=True) as ndb:
   # ... here some NDB operations
   ndb.schema.export_debug('ndb.schema')

Unlike ordinary table, limited with the number of network objects in the system, the events log tables are not limited. Do not enable the events logging in production, it may exhaust all the memory.

RTNL objects

NDB creates RTNL objects on demand, it doesn’t keep them all the time. References to created objects are linked to the ndb.<view>.cache set:

>>> ndb.interfaces.cache.keys()
[(('target', u'localhost'), ('index', 2)),
 (('target', u'localhost'), ('index', 39615))]

>>> [x['ifname'] for x in ndb.interfaces.cache.values()]
[u'eth0', u't2']

Object states

RTNL objects may be in several states:

  • invalid: the object does not exist in the system
  • system: the object exists both in the system and in NDB
  • setns: the existing object should be moved to another network namespace
  • remove: the existing object must be deleted from the system

The state transitions are logged in the state log:

>>> from pyroute2 import NDB
>>> ndb = NDB()
>>> c = ndb.interfaces.create(ifname='t0', kind='dummy').commit()
>>> c.state.events
[
   (1557752212.6703758, 'invalid'),
   (1557752212.6821117, 'system')
]

The timestamps allow to correlate the state transitions with the NDB log and the RTNL events log, in the case it was enabled.

Object snapshots

Before running any commit, NDB marks all the related records in the DB with a random value in the f_tflags DB field (tflags object field), and stores all the marked records in the snapshot tables. Shortly, the commit() is a snapshot() + apply() + revert() if failed:

>>> nic = ndb.interfaces['t0']
>>> nic['state']
'down'
>>> nic['state'] = 'up'
>>> snapshot = nic.snapshot()
>>> ndb.schema.snapshots
{
   'addresses_139736119707256': <weakref at 0x7f16d8391a98; to 'Interface' at 0x7f16d9c708e0>,
   'neighbours_139736119707256': <weakref at 0x7f16d8391a98; to 'Interface' at 0x7f16d9c708e0>,
   'routes_139736119707256': <weakref at 0x7f16d8391a98; to 'Interface' at 0x7f16d9c708e0>,
   'nh_139736119707256': <weakref at 0x7f16d8391a98; to 'Interface' at 0x7f16d9c708e0>,
   'p2p_139736119707256': <weakref at 0x7f16d8391a98; to 'Interface' at 0x7f16d9c708e0>,
   'ifinfo_bridge_139736119707256': <weakref at 0x7f16d8391a98; to 'Interface' at 0x7f16d9c708e0>,
   'ifinfo_bond_139736119707256': <weakref at 0x7f16d8391a98; to 'Interface' at 0x7f16d9c708e0>,
   'ifinfo_vlan_139736119707256': <weakref at 0x7f16d8391a98; to 'Interface' at 0x7f16d9c708e0>,
   'ifinfo_vxlan_139736119707256': <weakref at 0x7f16d8391a98; to 'Interface' at 0x7f16d9c708e0>,
   'ifinfo_gre_139736119707256': <weakref at 0x7f16d8391a98; to 'Interface' at 0x7f16d9c708e0>,
   'ifinfo_vrf_139736119707256': <weakref at 0x7f16d8391a98; to 'Interface' at 0x7f16d9c708e0>,
   'ifinfo_vti_139736119707256': <weakref at 0x7f16d8391a98; to 'Interface' at 0x7f16d9c708e0>,
   'ifinfo_vti6_139736119707256': <weakref at 0x7f16d8391a98; to 'Interface' at 0x7f16d9c708e0>,
   'interfaces_139736119707256': <weakref at 0x7f16d8391a98; to 'Interface' at 0x7f16d9c708e0>
}
>>> nic.apply()
...
>>> nic['state']
'up'
>>> snapshot.apply(rollback=True)
...
>>> nic['state']
'down'

Or same:

>>> nic = ndb.interfaces['t0']
>>> nic['state']
'down'
>>> nic['state'] = 'up'
>>> nic.commit()
>>> nic['state']
'up'
>>> nic.rollback()
>>> nic['state']
'down'

These snapshot tables are the objects’ state before the changes were applied.