restoring backup fails when db is not empty

Summary

When restoring backup to db that is not empty, everything fails.

Steps to reproduce

run backup restore on not empty mongo database

Expected behavior

backup restored

Actual behavior

backup fails

Relevant logs and/or screenshots

 ________________________________________________________
/ TASK [rocketchat : execute command in database service \
\ container]                                             /
 --------------------------------------------------------
    \                                  ___-------___
     \                             _-~~             ~~-_
      \                         _-~                    /~-_
             /^\__/^\         /~  \                   /    \
           /|  O|| O|        /      \_______________/        \
          | |___||__|      /       /                \          \
          |          \    /      /                    \          \
          |   (_______) /______/                        \_________ \
          |         / /         \                      /            \
           \         \^\\         \                  /               \     /
             \         ||           \______________/      _-_       //\__//
               \       ||------_-~~-_ ------------- \ --/~   ~\    || __/
                 ~-----||====/~     |==================|       |/~~~~~
                  (_(__/  ./     /                    \_\      \.
                         (_(___/                         \_____)_)

fatal: [rocketchat]: FAILED! => {"changed": true, "cmd": ["docker", "exec", "rocketchat-database", "mongorestore", "--archive=/dump/prod_rocketchat_backup.gz", "--gzip"], "delta": "0:00:15.134143", "end": "2017-03-16 07:50:37.310380", "failed": true, "rc": 1, "start": "2017-03-16 07:50:22.176237", "stderr": "2017-03-16T07:50:22.342+0000\tcreating intents for archive\n2017-03-16T07:50:22.380+0000\treading metadata for rocketchat.rocketchat_message from archive '/dump/prod_rocketchat_backup.gz'\n2017-03-16T07:50:22.380+0000\trestoring rocketchat.rocketchat_message from archive '/dump/prod_rocketchat_backup.gz'\n2017-03-16T07:50:25.118+0000\treading metadata for rocketchat.rocketchat_oembed_cache from archive '/dump/prod_rocketchat_backup.gz'\n2017-03-16T07:50:25.118+0000\trestoring rocketchat.rocketchat_oembed_cache from archive '/dump/prod_rocketchat_backup.gz'\n2017-03-16T07:50:25.378+0000\t     rocketchat.rocketchat_message  8.78MB\n2017-03-16T07:50:25.378+0000\trocketchat.rocketchat_oembed_cache  12.5MB\n2017-03-16T07:50:25.378+0000\t\n2017-03-16T07:50:25.419+0000\treading metadata for rocketchat.rocketchat_statistics from archive '/dump/prod_rocketchat_backup.gz'\n2017-03-16T07:50:25.420+0000\trestoring rocketchat.rocketchat_statistics from archive '/dump/prod_rocketchat_backup.gz'\n2017-03-16T07:50:26.256+0000
I DUŻO CZERWONEGO TUTAJ DALEJ

Possible fixes

add --drop flag to mongorestore command