Setting up MongoDB

Installation

Install latest STABLE MongoDB version, e.g.,

vi /etc/yum.repos.d/mongodb-org-3.2.repo

[mongodb-org-3.2]
name=MongoDB Repository
baseurl=https://repo.mongodb.org/yum/redhat/$releasever/mongodb-org/3.2/x86_64/
gpgcheck=1
enabled=1
gpgkey=https://www.mongodb.org/static/pgp/server-3.2.asc

yum update
yum install mongodb-org

Note. those packages get installed:

mongodb-org-shell
mongodb-org-tools
mongodb-org-mongos
mongodb-org-server
mongodb-org

(undeeded) just for the record, if you need to pin the version so it won’t get upgraded automaticly when doing yum upgrade,

#cd /etc/
#cp yum.conf yum.conf.dist
#vi yum.conf
#exclude=mongodb-org,mongodb-org-server,mongodb-org-shell,mongodb-org-mongos,mongodb-org-tools

Ref. https://docs.mongodb.com/master/tutorial/install-mongodb-on-red-hat/

Warning: service gets enabled by default at boot time. That SysV script is backward compatible on RHEL/CentOS version 7,

service mongod status
service mongod start
chkconfig --list | grep mongo
chkconfig mongod on

Increase the process & file limits for mongodb user only, hardcoded system-wide,

vi /etc/security/limits.d/99-mongodb-nproc.conf

mongod - fsize unlimited
mongod - cpu unlimited
mongod - as unlimited
mongod - nofile 64000
mongod - rss unlimited
mongod - nproc 64000
mongod - memlock unlimited

Not sure a server reboot is needed, try restarting mongodb first and if you still got the warnings with mongo command line, simply restart the server.

Refs.

• http://tehcbase.com/configuring-unix-ulimit-setting-for-mongodb/
• http://serverfault.com/questions/591812/how-to-set-ulimits-for-mongod
• https://docs.mongodb.com/manual/reference/ulimit/

Improve database performance by disabling Transparent Huge Pages (THP) using an additional init script loaded at startup,

vi /etc/init.d/disable-transparent-hugepages

#!/bin/sh
### BEGIN INIT INFO
# Provides:          disable-transparent-hugepages
# Required-Start:    $local_fs
# Required-Stop:
# X-Start-Before:    mongod mongodb-mms-automation-agent
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
# Short-Description: Disable Linux transparent huge pages
# Description:       Disable Linux transparent huge pages, to improve
#                    database performance.
### END INIT INFO

case $1 in
  start)
    if [ -d /sys/kernel/mm/transparent_hugepage ]; then
      thp_path=/sys/kernel/mm/transparent_hugepage
    elif [ -d /sys/kernel/mm/redhat_transparent_hugepage ]; then
      thp_path=/sys/kernel/mm/redhat_transparent_hugepage
    else
      return 0
    fi

    echo 'never' > ${thp_path}/enabled
    echo 'never' > ${thp_path}/defrag

    unset thp_path
    ;;
esac

chmod 755 /etc/init.d/disable-transparent-hugepages
chkconfig --add disable-transparent-hugepages
chkconfig --list | grep huge
/etc/init.d/disable-transparent-hugepages

restart the system as we’ve changed the limits (keep it simple),

shutdown -r now

and check,

cat /sys/kernel/mm/transparent_hugepage/enabled
cat /sys/kernel/mm/transparent_hugepage/defrag

both should return,

always madvise [**never**]

Ref. https://docs.mongodb.com/manual/tutorial/transparent-huge-pages/

Alternatively, just for the record, it’s also possible to proceed directly at kernel load time,

#cd /etc/sysconfig/
#cp grub grub.dist
#vi grub
#GRUB_CMDLINE_LINUX="crashkernel=auto rd.lvm.lv=VG0/root rhgb quiet net.ifnames=0 biosdevname=0 **transparent_hugepage=never**"
#(no need to reload with those sysconfig settings?)
#and reboot to check

Alternate pathes

If you need to locate the data & log folders on a specific location,

cd /data/
service mongod status
service mongod stop
mv /var/lib/mongo/ ./
mv /var/log/mongodb/ ./mongo.logs/
ls -al mongo/
ls -al mongo.logs/
#check the perms

cd /etc/
cp mongod.conf mongod.conf.dist
vi mongod.conf

systemLog:
  path: /data/mongo.logs/mongod.log

storage:
  dbPath: /data/mongo

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

Note. no need to change the pid location (/var/run/mongodb/mongod.pid). Note. bindIP can stay commented out unless you really want it to become a network service, you can ssh tunnel anyway against the localhost:27017 to use MongoChef or whatever to debug the db.

Double check the path (it’s normal the pid won’t show up), ownerships and permissions,

cd /etc/
grep -i path mongod.conf | awk '{print $2}' | xargs ls -lhFd
#chown -R mongod:mongod /data/databases/ /data/logs/mongodb/
#chmod 755 /data/mongo/ /data/mongo.logs/
#chmod 640 /data/mongo.logs/mongod.log

Ready to go

Let’s start the nifty daemon and watch the logs,

service mongod start
tail -F /data/mongo.logs/mongod.log

the last line as for daemon’s startup should report,

2016-<time> I NETWORK  [initandlisten] waiting for connections on port 27017

Maintenance / Operations

exclude package from conflicting repositories

e.g. make sure nodejs and mongodb are excluded from EPEL upgrades (those two package sets have their own repo),

cd /etc/yum.repos.d/
vi epel.repo

[epel]
...
exclude=libuv* nodejs* npm* mongodb-org*

then to proceed with the MongoDB upgrades, simply,

yum upgrade

and if you see that MongoDB was indeed upgraded, schedule a database restart,

service mongod restart

as long as those are minor updates (repo is pointing to minor release changes), no database migration/update process is required. For major upgrades see the official doc.

also if NodeJS was upgraded, schedule an application restart,

cd /data/...
npm stop
npm start

NodeJS repo is also setup to stick to a major release so there should not be any code breaks.