Install the MongoDB software

Red Hat does not offer an up-to-date version of MongoDB on RHEL 7, but MongoDB, Inc. offers its own set of repositories from which the most current version can be installed.

Note: Although the master build server will not be a member of the replica set, the MongoDB software will be installed there to facilitate customizing configuration files and distributing them to the replica set members, and to enable use of the mongo shell client application. In each section below, instructions are provided to indicate on which server(s) that step should be performed.

Install the MongoDB repository

As of this writing the latest, stable version of MongoDB is 3.6, originally released in December 2017. To install MongoDB 3.6 with yum, create the file /etc/yum.repos.d/mongodb-org-3.6.repo on the master build server (casdev-master) with the following contents:

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

Then copy the new file to each of the CAS servers by running the commands

casdev-master# for i in 01 02 03
> do
> scp -p /etc/yum.repos.d/mongodb-org-3.6.repo casdev-srv${i}:/etc/yum.repos.d/mongodb-org-3.6.repo
> done
mongodb-org-3.6.repo                          100%  200   273.9KB/s   00:00
mongodb-org-3.6.repo                          100%  200   251.1KB/s   00:00
mongodb-org-3.6.repo                          100%  200   255.4KB/s   00:00
casdev-master#  

Install MongoDB

Run the command

# yum -y install mongodb-org

on the master build server (casdev-master) and each of the CAS servers (casdev-srv01, casdev-srv02, and casdev-srv03) to install MongoDB.

Correct directory permissions

The default MongoDB installation creates the MongoDB data directory and MongoDB log directory with permissions that allow all users on the system to access them. However, only the mongod user and mongod group actually need access to these directories, so access for other users should be removed. Run the command

# chmod -R o= /var/lib/mongo /var/log/mongodb

on the master build server (casdev-master) and each of the CAS servers (casdev-srv01, casdev-srv02, and casdev-srv03) to correct the directory permissions.

Configure `logrotate`

By default, mongod will keep writing to the same log file until it is told not to; there is no pre-configured scheme for rotating logs. To correct this, configure the logroate program, which is probably already being used to rotate various system log files, to rotate /var/log/mongodb/mongod.log as well.

Create the file /etc/logrotate.d/mongod on the master build server (casdev-master) with the following contents:

/var/log/mongodb/mongod.log
{
    daily
    dateext
    dateformat -%Y-%m-%d
    dateyesterday
    extension .log
    missingok
    notifempty
    rotate 30
    create 0640 mongod mongod
    sharedscripts
    postrotate
        /bin/kill -SIGUSR1 $(cat /var/run/mongodb/mongod.pid)
    endscript
}

This will rotate mongod.log every day, moving the current log file to mongod-YYYY-MM-DD.log. Since logrotate typically runs in the wee hours of the morning, the dateyesterday directive tells it to use yesterday’s date for the file name, since that’s when most of the log entries will come from. The last 30 days’ worth of log files will be kept; older files will be deleted automatically. Once the file has been rotated, logrotate will signal mongod to switch to the new log file.

Run the command

casdev-master# logrotate -df /etc/logrotate.d/mongod
reading config file /etc/logrotate.d/mongod
extension is now .log
Allocating hash table for state file, size 15360 B

Handling 1 logs

rotating pattern: /var/log/mongodb/mongod.log
 forced from command line (30 rotations)
empty log files are not rotated, old logs are removed
considering log /var/log/mongodb/mongod.log
  log needs rotating
rotating log /var/log/mongodb/mongod.log, log->rotateCount is 30
Converted ' -%Y-%m-%d' -> '-%Y-%m-%d'
dateext suffix '-2018-04-29'
glob pattern '-[0-9][0-9][0-9][0-9]-[0-9][0-9]-[0-9][0-9]'
glob finding old rotated logs failed
fscreate context set to system_u:object_r:mongod_log_t:s0
renaming /var/log/mongodb/mongod.log to /var/log/mongodb/mongod-2018-04-29.log
creating new /var/log/mongodb/mongod.log mode = 0640 uid = 994 gid = 992
running postrotate script
running script with arg /var/log/mongodb/mongod.log
: "
        /bin/kill -SIGUSR1 $(cat /var/run/mongodb/mongod.pid)
"
casdev-master#  

to check the syntax of the file and confirm that it will do what you expect. Then copy the new file to each of the CAS servers by running the commands

casdev-master# for i in 01 02 03
> do
> scp -p /etc/logrotate.d/mongod casdev-srv${i}:/etc/logrotate.d/mongod
> done
mongod                                        100%  293   400.8KB/s   00:00
mongod                                        100%  293   363.6KB/s   00:00
mongod                                        100%  293   397.7KB/s   00:00
casdev-master#  

Disable the `mongod` service on the master build server

Since the master build server will not be part of the replica set, it does not need to run the MongoDB server (mongod). Run the command

casdev-master# systemctl disable mongod
Removed symlink /etc/systemd/system/multi-user.target.wants/mongod.service.
casdev-master#  

on the master build server (casdev-master) to prevent mongod from being started when the system boots.

References

MongoDB: Install MongoDB Community Edition on Red Hat Enterprise or CentOS Linux