Charmed MongoDB Tutorials > Deploy a replica set > 3. Access a replica set

Access a replica set

MongoDB databases can be accessed via the mongosh, the MongoDB shell. This shell comes pre-installed in the units hosting the Charmed MongoDB application as charmed-mongodb.mongosh.

Connecting to the database requires a Uniform Resource Identifier (URI). MongoDB expects a MongoDB-specific URI that contains information used to authenticate us to the database.

In this part of the tutorial, we will fetch all the information needed to generate a URI that will grant us access to MongoDB, connect to the mongo shell, and create a test database.

Summary

• Retrieve URI data
  • Username | $DB_USERNAME
  • Password | $DB_PASSWORD
  • Hosts | $HOST_IP
  • Database name | $DB_NAME
  • Replica set name | $REPL_SET_NAME
  • Generate the full URI
• Connect to the mongo shell via URI
• Create a database

Retrieve URI data

To access MongoDB via mongos, we need to build a URI of the format

mongodb://$DB_USERNAME:$DB_PASSWORD@$HOST_IP/$DB_NAME?replicaSet=$REPL_SET_NAME

Connecting via URI requires that you know the values for username, password, hosts, database name, and the replica set name. We will show you how to retrieve the necessary fields and set them to environment variables.

Username | $DB_USERNAME

In this case, we are using the operator user to connect to MongoDB directly. Use operator as the username:

export DB_USERNAME="operator"

The operator user is the admin user in Charmed MongoDB.

Password | $DB_PASSWORD

Run the get-password action on the Charmed MongoDB application:

juju run mongodb/leader get-password

The command should output:

Running operation 5 with 1 task
  - task 6 on unit-mongodb-0

Waiting for task 6...
password: 9JLjd0tuGngW5xFKWWbo0Blxyef0oGec

The command below sets the environment variable automatically by running get-password and filtering the password field:

export DB_PASSWORD=$(juju run mongodb/leader get-password  | grep password|  awk '{print $2}')

Hosts | $HOST_IP

The hosts are the units hosting the MongoDB application. The host’s IP address can be found with juju status:

Model     Controller  Cloud/Region         Version  SLA          Timestamp
tutorial  overlord    localhost/localhost  3.1.6   unsupported  11:31:16Z

App      Version  Status  Scale  Charm    Channel   Rev  Exposed  Message
mongodb           active      1  mongodb  5/edge   96  no       Replica set primary

Unit        Workload  Agent  Machine  Public address  Ports      Message
mongodb/0*  active    idle   0        <host IP>    27017/tcp  Replica set primary

Machine  State    Address       Inst id        Series  AZ  Message
0        started  10.23.62.156  juju-d35d30-0  jammy       Running

Set the variable HOST_IP to the IP address for mongodb/0:

export HOST_IP=$(juju exec --unit mongodb/0 -- hostname -I | awk '{print $1}')

Database name | $DB_NAME

In this case, we are connecting to the admin database. Use admin as the database name.

Once we access the database via the MongoDB URI, we will create a test-db database to store data.

export DB_NAME="admin"

Replica set name | $REPL_SET_NAME

The replica set name is the name of the application on Juju hosting MongoDB. The application name in this tutorial is mongodb. Use mongodb as the replica set name.

export REPL_SET_NAME="mongodb"

Generate the full URI

To summarize:

export DB_USERNAME="operator"
export DB_PASSWORD=$(juju run mongodb/leader get-password  | grep password|  awk '{print $2}')
export HOST_IP=$(juju exec --unit mongodb/0 -- hostname -I | awk '{print $1}')
export DB_NAME="admin"
export REPL_SET_NAME="mongodb"

We can create the URI with:

export URI=mongodb://$DB_USERNAME:$DB_PASSWORD@$HOST_IP/$DB_NAME?replicaSet=$REPL_SET_NAME

Now echo the URI and save it, as you won’t be able to rely on this environment variable when you ssh into a unit in the next step.

echo $URI

Connect via MongoDB URI

To access the unit hosting MongoDB, ssh into it:

juju ssh mongodb/0

If at any point you’d like to leave the unit, type exit.

While ssh’d into mongodb/0, we can access mongo using the URI that we saved in the previous step.

charmed-mongodb.mongosh <saved URI>

You should now see something similar to:

Current Mongosh Log ID: 6389e2adec352d5447551ae0
Connecting to:    mongodb://<credentials>@10.23.62.156/admin?replicaSet=mongodb&appName=mongosh+1.6.1
Using MongoDB:    5.0.14
Using Mongosh:    1.6.1

For mongosh info see: https://docs.mongodb.com/mongodb-shell/

To help improve our products, anonymous usage data is collected and sent to MongoDB periodically (https://www.mongodb.com/legal/privacy-policy).
You can opt-out by running the disableTelemetry() command.

------
   The server generated these startup warnings when booting
   2022-12-02T11:24:05.416+00:00: Using the XFS filesystem is strongly recommended with the WiredTiger storage engine. See http://dochub.mongodb.org/core/prodnotes-filesystem
------

------
   Enable MongoDB's free cloud-based monitoring service, which will then receive and display
   metrics about your deployment (disk utilization, CPU, operation statistics, etc).

   The monitoring data will be available on a MongoDB website with a unique URL accessible to you
   and anyone you share the URL with. MongoDB may use this information to make product
   improvements and to suggest MongoDB products and deployment options to you.

   To enable free monitoring, run the following command: db.enableFreeMonitoring()
   To permanently disable this reminder, run the following command: db.disableFreeMonitoring()
------

mongodb [primary] admin>

You can now interact with MongoDB directly using any MongoDB commands. For example, entering

show dbs

should output something like:

admin   172.00 KiB
config  120.00 KiB
local   404.00 KiB

Create a database

Now that we have access to MongoDB, we can create a database named test-db.

In the MongoDB shell, run:

use test-db

Now create a user called testUser with read/write access to test-db:

db.createUser({
  user: "testUser",
  pwd: "password",
  roles: [
    { role: "readWrite", db: "test-db" }
  ]
})

You can verify that you added the user correctly by entering the command show users into the mongo shell. This will output:

[
  {
    _id: 'test-db.testUser',
    userId: new UUID("6e841e28-b1bc-4719-bf42-ba4b164fc546"),
    user: 'testUser',
    db: 'test-db',
    roles: [ { role: 'readWrite', db: 'test-db' } ],
    mechanisms: [ 'SCRAM-SHA-1', 'SCRAM-SHA-256' ]
  }
]

Feel free to test out any other MongoDB commands. When you’re ready to leave the MongoDB shell, just type exit. You will be back in the host of Charmed MongoDB (mongodb/0).

Exit this host by once again typing exit. Now you will be in your original shell where you can interact with Juju and LXD.

Next step: 4. Scale your replicas