mongo_lag.py

import pymongo

uri = "mongodb://user:pass@localhost:27017/admin"
conn = pymongo.MongoClient(uri)
db = conn['admin']
db_stats = db.command({'replSetGetStatus'  :1})

server_secondary = 'name_server:27017'
primary_optime = 0
secondary_optime = 0


for key in db_stats['members'] : 
    print key
    print '---------'
    if (key['stateStr'] == 'SECONDARY' and key['name'] == server_secondary):
        secondary = key['name']
        secondary_optime = key['optimeDate']
    if key['stateStr'] == 'PRIMARY' : 
        primary = key['name']
        primary_optime =key['optimeDate']

print 'primary_optime : %s - %s ' %(str(primary_optime), str(primary))
print 'secondary_optime : %s - %s ' %(str(secondary_optime), str(secondary))

seconds_lag = (primary_optime - secondary_optime ).total_seconds()
#total_seconds() userd to get the lag in seconds rather than datetime object
print 'secondary_lag : ' + str(seconds_lag)