MongoDB

Setting Up

Installing

Debian/Ubuntu

MongoDB provides instructions for installing on Debian/Ubuntu. The short version: don't do apt-get install mongodb.

Here's what you do:

• Add the mongodb aptitude repositories to your aptitude
• Update your aptitude
• Install a mongodb package from mongodb.org

sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv 2930ADAE8CAF5059EE73BB4B58712A2291FA4AD5
echo "deb [ arch=amd64,arm64 ] https://repo.mongodb.org/apt/ubuntu xenial/mongodb-org/3.6 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-3.6.list
sudo apt-get update
sudo apt-get install -y mongodb-org

These assume you have ubuntu xenial, see link [1] for other LTS releases.

Fixing Stupid Issues

On Ubuntu there is a stupid issue with the startup service - a mistake.

Edit the file /lib/systemd/system/mongod.service

Change the line

ExecStart=/usr/bin/mongod -f /etc/mongod.conf

to the following (note the name of the conf file):

ExecStart=/usr/bin/mongod -f /etc/mongodb.conf

Re-load the service from the edited file by running:

sudo systemctl start mongod

Pretty stupid, ey?

Homebrew

Was able to install this ok with Homebrew: https://docs.mongodb.com/manual/tutorial/install-mongodb-on-os-x/#install-mongodb-community-edition-with-homebrew

brew update
brew install mongodb

or to install the development version:

brew update
brew install mongodb --devel

Configuring

Link to documentation page on config options: https://docs.mongodb.com/manual/reference/configuration-options/

By default, MongoDB will not require a config file, and if you don't specify one, it makes some weird decisions.

To start mongodb with a specified config file, use the --config or -f options:

mongod --config /etc/mongod.conf
mongod -f /etc/mongod.conf

Core mongodb config sections:

• systemLog
• net

systemLog

# default:

systemLog:
  destination: file
  path: /var/log/mongodb/mongod.log
  logAppend: true

can also set verbosity (0-5):

systemLog:
    destination: file
    path: /var/log/mongodb/mongod.log
    verbosity: 2
    logRotate: rename

If using logrotate util, set logRotate: reopen

Can further customize log behavior for specific components (access, commands, etc.)

net

net:
    port: 27017
    bindIp: 10.0.0.1
    ipv6: True

There are also several options for SSL. Those go into an ssl subsection of the net section of the config file.

Starting

MongoDB can be started with systemd, or using the init.d startup scripts. I hate systemd so I went with the latter.

Start by creating the directory where MongoDB will keep all of its data. For example, I used /opt/mongodb. Set the permissions so that the mongodb user/group can read/write to this directory:

sudo chown -R mongodb:mongodb mongodb/

Now start the service, which is defined in /etc/init.d/mongodb:

sudo service mongodb start

You can issue the status command in place of the start command to check if the process is running:

$ sudo service mongodb status
● mongodb.service - LSB: An object/document-oriented database
   Loaded: loaded (/etc/init.d/mongodb; bad; vendor preset: enabled)
   Active: active (running) since Tue 2018-01-30 16:59:10 PST; 1min 38s ago
     Docs: man:systemd-sysv-generator(8)
  Process: 1962 ExecStart=/etc/init.d/mongodb start (code=exited, status=0/SUCCESS)
 Main PID: 13596 (code=exited, status=0/SUCCESS)
   CGroup: /system.slice/mongodb.service
           └─1973 /usr/bin/mongod --config /etc/mongodb.conf

Jan 30 16:59:09 jupiter systemd[1]: Starting LSB: An object/document-oriented database...
Jan 30 16:59:09 jupiter mongodb[1962]:  * Starting database mongodb
Jan 30 16:59:10 jupiter mongodb[1962]:    ...done.
Jan 30 16:59:10 jupiter systemd[1]: Started LSB: An object/document-oriented database.

You can also turn on logging, and look at the log files in /var/log/mongodb/mongodb.log

Selecting an Interface

The first thing you have to decide before interacting with the database is how you want to interact.

The mongodb shell is a javascript shell that can be used from a command line on the mongodb server.

Mongodb also has python language bindings. there are multiple non-mongo-provided third party APIs and libraries too, so there are multiple options.

Basic CRUD Operations

MongoDB performs CRUD (create, read, update, delete) transactions/operations on the data that it stores.

Create (Insert)

To insert documents into a collection:

• db.collection.insertOne()
• db.collection.insertMany()

Example: db.users.insertOne({name:"Sue", age:26})

Read (Query)

To read documents from a collection, use the find function:

• db.collection.find()

Example: db.users.find({age:{$gt:18}})

Update

To update documents in a collection:

• db.collection.updateOne()
• db.collection.updateMany()
• db.collection.replaceOne()

Example: db.users.updateMany( {age:{$lt:18}, $set: {status: "reject"}} )

Delete

Delete documents one at a time or en masse:

• db.collection.deleteOne()
• db.collection.deleteMany()

Monitoring

MongoDB as a Monitoring Target

MongoDB has several mechanisms for monitoring the state of the database (per second operations, cache sizes, disk and memory usage, etc.)

Utilities like Netdata and Collectd have plugins written for MongoDB that can collect this information as part of scraping the system status.

MongoDB as a Monitoring Data Store

The Write_MongoDB plugin provides a plugin for collectd to write its data to MongoDB.

Plugin link: https://collectd.org/wiki/index.php/Plugin:Write_MongoDB

References

pymodm: https://pymodm.readthedocs.io/en/latest/getting-started.html

Database design patterns: https://docs.mongodb.com/manual/applications/data-models/

Cheat sheet: https://blog.codecentric.de/files/2012/12/MongoDB-CheatSheet-v1_0.pdf

Related Page

• MongoExpress