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https://github.com/rodneyosodo/mongodb_replicaset

A simple application that show how to replica mongodb
https://github.com/rodneyosodo/mongodb_replicaset

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A simple application that show how to replica mongodb

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README 

        
# Mongodb REPLICATION



### Disclaimer

I don’t know about anything i wrote



### What is database replication

It is a technique where an instance of a database is exactly copied to another location.



There are many types of database replication for now we will look at physical replication. Physical replication alllows you to replicate the entire database cluster onto another server



Synchronous replication creates copies of data in real time. As synchronous replication is continuously creating data in real time, it tends to be very expensive. However, it is also very reliable in the event of a disaster.

Synchronous replication requires capable computation capacity because it creates latency and slows the primary systems. It does this by using WAL to stay in sync. It replicates everything on the cluster



### Advantages of Replication



- __High Availability__ : when one node or the primary node goes down, another node in the cluster can be switch to and depended on for serving of workload

- __Increased read performance__ : Multiple machines provide greater processing power and data can be spread across multiples machines on a network.This allows to vastly improve your application’s read performance.

- __Greater scalability__ : As your user base grows and report complexity increases, your resources can grow.



## Lets start



```We will do this by using docker.```



1. Creating a single database

2. Now lets stop the docker then create another database using docker compose

```yaml

version: '3.0'

services:

 demo-mongo-worker-3:

   image: 'mongo:latest'

   ports:

     - '27018:27017'

   restart: always

```

3. Then we run docker-compose up

4. We ran docker-compose down to stop the mongodb container

5. Finally let us create a replica set 



We will create 1 primary and 3 secondary nodes. If the primary goes down all the other will vote to elect the primary. Each node will require a data volume and also a shared volume for the nodes to talk together.



For this to work we will need volumes  and a single network of type bridge network.



__For our services.__

We need a docker container to generate a new key every time the cluster is started. First we create an openssl image which will be responsible to create our keyfile.



Our primary we will mount the shared volume and its volume. We will also set its password and username with environment variables. We will map to 2717 since am runnig mongodb in my system.

For secondary we will only change the port maping name and also shared volume.

6. If we run this it should bring up the cluster.



Our compose file is here

```yaml

version: '3.0'

services:

 demo-mongo-keys:

   image: openssl

   build: openssl/.

   volumes:

     - 'demo-mongo-keys:/mongo-conf'

   command: bash -c "openssl rand -base64 741 > /mongo-conf/mongodb-keyfile; chmod 600 /mongo-conf/mongodb-keyfile; chown 999 /mongo-conf/mongodb-keyfile"

  demo-mongo-primary:

   image: 'mongo:latest'

   volumes:

     - 'demo-mongo-keys:/opt/keyfile'

     - 'demo-mongo-data-0:/data/db'

   env_file: ./mongod.env

   ports:

     - '2717:27017'

   command: mongod --auth --keyFile /opt/keyfile/mongodb-keyfile --replSet demo-replica-set

   depends_on:

     - demo-mongo-keys

   networks:

     demo-replica-set:

 demo-mongo-worker-1:

   image: 'mongo:latest'

   volumes:

     - 'demo-mongo-keys:/opt/keyfile'

     - 'demo-mongo-data-1:/data/db'

   env_file: ./mongod.env

   ports:

     - '27018:27017'

   command: mongod --auth --keyFile /opt/keyfile/mongodb-keyfile --replSet demo-replica-set

   depends_on:

     - demo-mongo-keys

   networks:

     demo-replica-set:

 

 demo-mongo-worker-2:

   image: 'mongo:latest'

   volumes:

     - 'demo-mongo-keys:/opt/keyfile'

     - 'demo-mongo-data-2:/data/db'

   env_file: ./mongod.env

   ports:

     - '27019:27017'

   command: mongod --auth --keyFile /opt/keyfile/mongodb-keyfile --replSet demo-replica-set

   depends_on:

     - demo-mongo-keys

   networks:

     demo-replica-set:

 

 demo-mongo-worker-3:

   image: 'mongo:latest'

   volumes:

     - 'demo-mongo-keys:/opt/keyfile'

     - 'demo-mongo-data-3:/data/db'

   env_file: ./mongod.env

   ports:

     - '27020:27017'

   command: mongod --auth --keyFile /opt/keyfile/mongodb-keyfile --replSet demo-replica-set

   depends_on:

     - demo-mongo-keys

   networks:

     demo-replica-set:

 

volumes:

 demo-mongo-keys:

 demo-mongo-data-0:

 demo-mongo-data-1:

 demo-mongo-data-2:

 demo-mongo-data-3:

 

networks:

 demo-replica-set:

   driver: bridge

   ipam:

     driver: default

     config:

       - subnet: 172.10.99.0/24

```

 



7. We will login to the primary define our replica set and then make it the primary.

```sh

docker-compose exec demo-mongo-primary mongo -u "root" -p "password"

```

8. Instatiate the replica set 

```javascript

rs.initiate(

    {"_id" : "tut12-replica-set",

    "members" : [

        {"_id" : 0,"host" : "tut12-mongo-primary:27017"},

        {"_id" : 1,"host" : "tut12-mongo-worker-1:27017"},

        {"_id" : 2,"host" : "tut12-mongo-worker-2:27017"},

        {"_id" : 3,"host" : "tut12-mongo-worker-3:27017"}

        ]

    });

 ```

 

9. Set the priority of the master over the other nodes

```sh

conf = rs.config();

```

```sh

conf.members[0].priority = 2;

```

```sh

rs.reconfig(conf);

```

 

10. Now lets add some data and check to set it.



    We head over to [json-generator](https://www.json-generator.com/) to generate json data to push to our mongodb

```

[

  '{{repeat(10000)}}',

  {

    _id: '{{objectId()}}',

    index: '{{index()}}',

    guid: '{{guid()}}',

    isActive: '{{bool()}}',

    balance: '{{floating(1000, 4000, 2, "$0,0.00")}}',

    picture: 'http://placehold.it/32x32',

    age: '{{integer(20, 40)}}',

    eyeColor: '{{random("blue", "brown", "green")}}',

    name: '{{firstName()}} {{surname()}}',

    gender: '{{gender()}}',

    company: '{{company().toUpperCase()}}',

    email: '{{email()}}',

    phone: '+1 {{phone()}}',

    address: '{{integer(100, 999)}} {{street()}}, {{city()}}, {{state()}}, {{integer(100, 10000)}}',

    about: '{{lorem(1, "paragraphs")}}',

    registered: '{{date(new Date(2014, 0, 1), new Date(), "YYYY-MM-ddThh:mm:ss Z")}}',

    latitude: '{{floating(-90.000001, 90)}}',

    longitude: '{{floating(-180.000001, 180)}}'

  }

]

```

11. We will use the python script to push data to the database

    We finally run the bash file to push data

12. Check the data base

![picture alt]( https://github.com/0x6f736f646f/mongodb_replicaset/blob/master/assets/image.png "Screenshot of database")



### Considerations

This replica set consists of 3 nodes as you can see.However, if you decide to go with an even number say 4 members, deploy an arbiter so that the set has an odd number of voting members.Voting is usually conducted by cluster members to elect a primary node and so adding an arbiter ensures no ties are risen during voting.