cat /var/log/mongodb/mongod.log | grep "Successfully connected to mongo1.production.internal:27017" | sort | uniq

2020-10-16T00:06:57.310+0000 I NETWORK [LogicalSessionCacheRefresh] Successfully connected to mongo1.production.internal:27017 (527 connections now open to mongo1.production.internal:27017 with a 0 second timeout)
2020-10-16T04:06:57.422+0000 I NETWORK [LogicalSessionCacheRefresh] Successfully connected to mongo1.production.internal:27017 (528 connections now open to mongo1.production.internal:27017 with a 0 second timeout)
2020-10-16T08:06:56.913+0000 I NETWORK [LogicalSessionCacheRefresh] Successfully connected to mongo1.production.internal:27017 (529 connections now open to mongo1.production.internal:27017 with a 0 second timeout)

 
mongod --version

db version v4.0.5
git version: 3739429dd92b92d1b0ab120911a23d50bf03c412
OpenSSL version: OpenSSL 1.0.2n 7 Dec 2017
allocator: tcmalloc
modules: none
build environment:
distmod: ubuntu1404
distarch: x86_64
target_arch: x86_64

mongo --version

git version: 3739429dd92b92d1b0ab120911a23d50bf03c412
OpenSSL version: OpenSSL 1.0.2n 7 Dec 2017
allocator: tcmalloc
modules: none
build environment:
distmod: ubuntu1404
distarch: x86_64
target_arch: x86_64