Setting up an EC2 Image for a MongoDB Replica Set from Scratch

Image and Basic Packages

Start with an Amazon Linux 2 AMI (HVM), SSD Volume Type - ami-0fad7378adf284ce0 (64-bit x86) image.

Add the yum repository for MongoDB 3.6 by creating /etc/yum.repos.d/mongodb-org-3.6.repo as follow:

[mongodb-org-3.6]
name=MongoDB Repository
baseurl=https://repo.mongodb.org/yum/amazon/2013.03/mongodb-org/3.6/x86_64/
gpgcheck=1
enabled=1
gpgkey=https://www.mongodb.org/static/pgp/server-3.6.asc

Then:

yum install -y mongodb-org-server mongodb-org-mongos mongodb-org-shell mongodb-org-tools
mkfs.xfs /dev/nvme0n1
mount /dev/nvme0n1 /var/lib/mongo

MongoDB Set-Up

In file /etc/mongod.conf comment the line

#  bindIp: 127.0.0.1  # Listen to local interface only, comment to listen on all interfaces.

and instead add

bindIp: 0.0.0.0

so that MongoDB listens on all interfaces, not only localhost. Furthermore, set the directoryPerDB property to true and provide a replication set name using the replication.replSetName property.

Here is the full /etc/mongod.conf file:

# mongod.conf

# for documentation of all options, see:
#   http://docs.mongodb.org/manual/reference/configuration-options/

# where to write logging data.
systemLog:
  destination: file
  logAppend: true
  path: /var/log/mongodb/mongod.log

# Where and how to store data.
storage:
  dbPath: /var/lib/mongo
  journal:
    enabled: true
  directoryPerDB: true
#  engine:
#  mmapv1:
#  wiredTiger:

# how the process runs
processManagement:
  fork: true  # fork and run in background
  pidFilePath: /var/run/mongodb/mongod.pid  # location of pidfile
  timeZoneInfo: /usr/share/zoneinfo

# network interfaces
net:
  port: 27017
#  bindIp: 127.0.0.1  # Listen to local interface only, comment to listen on all interfaces.
  bindIp: 0.0.0.0

#security:

#operationProfiling:

replication:
  replSetName: live

#sharding:

## Enterprise-Only Options

#auditLog:

#snmp:

Before being able to start the mongod service, more configuration is required:

chown mongod /var/lib/mongo/
chgrp mongod /var/lib/mongo/

will change the ownerships of the directory mounted from ephemeral storage accordingly, so the MongoDB daemon can write to it. The execute systemctl start mongod.service to launch the MongoDB process.

MongoDB Replica Set Configuration

Connect to the MongoDB on that instance, then issue the command rs.initiate() in order to turn the instance into the "seed" of a replica set. You can then, for the time being, quit() the mongo shell. Re-connecting, e.g., with mongo "mongodb://localhost:27017/?replicaSet=live", will show the PRIMARY of the new replica set.