Binding specific ips with Mongodb

I am using Mongodb 3.6.3 on Centos 7. I am running the below command: sudo mongod --storageEngine wiredTiger --dbpath /data --bind_ip_all --logpath /var/log/mongodb/mongod.log --fork and everything will work just fine. Except, binding all is not secure enough. I used to received a logging error when I tried --bind_ip 127.0.0.1,privateIP but discovered that the error would disappear when I did bind_ip [127.0.0.1,privateIP]. However, when I tried to connect to mongo locally it would fail and through a my site, it would sit there until it timed out. I checked sudo netstat -plnt | egrep mongodand then nothing showed up, which although it successfully forked the mongod process, it did not bind to any of the specified ips. For reference, when I tried the same command on on the --bind_ip_all version it returned tcp 0 0 0.0.0.0:27017 0.0.0.0:* LISTEN 1645/mongod. My question is, why did --bind_ip ips fail to bind to the specified ips? Side Note - when binding ips, should I bind my elastic ip or my private one?