Deploying a MongoDB Cluster Replicat Set For Development Environment

Publicado em por Jone Jarouj

Continuing with MongoDB article, our last one, we beginning setting the SO and installing MongoDB database. Now, we are going to set directories for 3 different instances, and create 3 different mongod.conf running on these directories.

First, lets create the directories:

[root@mongodbsrv ~]$ mkdir -p /srv/mongodb/rs0-0  /srv/mongodb/rs0-1 /srv/mongodb/rs0-2

Now, lets create .conf files:

[root@mongodbsrv ~]$ vim /etc/mongod_rs0-0.conf
replication:
   replSetName: "rs0"
   oplogSizeMB: 128
net:
   bindIp: localhost,mongodbsrv|192.168.1.221
   port: 27017
storage:
   dbPath: /srv/mongodb/rs0-0 
processManagement:
  fork: true
  pidFilePath: /srv/mongodb/rs0-0/mongod.pid
systemLog:
  destination: file
  path: "/srv/mongodb/rs0-0/mongod.log"
  logAppend: true
[root@mongodbsrv ~]$ cp /etc/mongod_rs0-0.conf /etc/mongod_rs0-1.conf 
[root@mongodbsrv ~]$ cp /etc/mongod_rs0-0.conf /etc/mongod_rs0-2.conf

Lets modify each file for each MongoDB instance: 

[root@mongodbsrv ~]$ vim /etc/mongod_rs0-1.conf
replication:
   replSetName: "rs0"
   oplogSizeMB: 128
net:
   bindIp: localhost,mongodbsrv|192.168.1.221
   port: 27018
storage:
   dbPath: /srv/mongodb/rs0-1
processManagement:
  fork: true
  pidFilePath: /srv/mongodb/rs0-1/mongod.pid
systemLog:
  destination: file
  path: "/srv/mongodb/rs0-1/mongod.log"
  logAppend: true
[root@mongodbsrv ~]$ vim /etc/mongod_rs0-2.conf
replication:
   replSetName: rs0
   oplogSizeMB: 128
net:
   bindIp: localhost,mongodbsrv|192.168.1.221
   port: 27019
storage:
   dbPath: /srv/mongodb/rs0-2
processManagement:
  fork: true
  pidFilePath: /srv/mongodb/rs0-2/mongod.pid
systemLog:
  destination: file
  path: "/srv/mongodb/rs0-2/mongod.log"
  logAppend: true

Lets first stop and removing mongod service, if running:

[root@mongodbsrv ~]$ systemctl stop mongod
[root@mongodbsrv ~]$ systemctl status mongod
○ mongod.service - MongoDB Database Server
     Loaded: loaded (/usr/lib/systemd/system/mongod.service; enabled; preset: disabled)
     Active: inactive (dead) since Sun 2026-03-22 21:07:49 -03; 48s ago
   Duration: 31min 4.533s
       Docs: https://docs.mongodb.org/manual
    Process: 1096 ExecStart=/usr/bin/mongod $OPTIONS (code=exited, status=0/SUCCESS)
   Main PID: 1096 (code=exited, status=0/SUCCESS)
        CPU: 14.865s

Mar 22 20:36:44 mongodbsrv systemd[1]: Started MongoDB Database Server.
Mar 22 20:36:44 mongodbsrv mongod[1096]: {"t":{"$date":"2026-03-22T23:36:44.535Z"},"s":"I",  "c":"CONTROL",  "id":10181001,"ctx":"main","msg":"Unable to open procfs path, falling back to default value","attr":{"p>
Mar 22 20:36:44 mongodbsrv mongod[1096]: {"t":{"$date":"2026-03-22T23:36:44.535Z"},"s":"I",  "c":"CONTROL",  "id":7484500, "ctx":"main","msg":"Environment variable MONGODB_CONFIG_OVERRIDE_NOFORK == 1, overriding >
Mar 22 21:07:48 mongodbsrv systemd[1]: Stopping MongoDB Database Server...
Mar 22 21:07:49 mongodbsrv systemd[1]: mongod.service: Deactivated successfully.
Mar 22 21:07:49 mongodbsrv systemd[1]: Stopped MongoDB Database Server.
Mar 22 21:07:49 mongodbsrv systemd[1]: mongod.service: Consumed 14.865s CPU time, 216.9M memory peak.
[root@mongodbsrv ~]$ systemctl disable mongod
Removed "/etc/systemd/system/multi-user.target.wants/mongod.service".

We can start the instances to test if everything its ok:

[root@mongodbsrv ~]$ mongod --config /etc/mongod_rs0-0.conf
[root@mongodbsrv ~]$ mongod --config /etc/mongod_rs0-1.conf
[root@mongodbsrv ~]$ mongod --config /etc/mongod_rs0-2.conf

Check the processes:

[root@mongodbsrv ~]$ ps -ef |grep mongod
pcp         2878       1  0 20:36 ?        00:00:00 /usr/bin/pmie -b -m pmie_check -F -P -l /var/log/pcp/pmie/mongodbsrv/pmie.log -c config.default
root       14448       1  1 21:16 ?        00:00:05 mongod --config /etc/mongod_rs0-0.conf
root       14632       1  4 21:22 ?        00:00:00 mongod --config /etc/mongod_rs0-1.conf
root       14701       1  6 21:22 ?        00:00:00 mongod --config /etc/mongod_rs0-2.conf
root       14773    8796  0 21:22 pts/0    00:00:00 grep --color=auto mongod

We can start the Replicaset configuration:

[root@mongodbsrv ~]$ mongosh --port 27017
Current Mongosh Log ID:	69c0880b4abd0c057959b253
Connecting to:		mongodb://127.0.0.1:27017/?directConnection=true&serverSelectionTimeoutMS=2000&appName=mongosh+2.8.1
Using MongoDB:		8.0.20
Using Mongosh:		2.8.1

For mongosh info see: https://www.mongodb.com/docs/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
   2026-03-22T21:16:49.489-03:00: Access control is not enabled for the database. Read and write access to data and configuration is unrestricted
   2026-03-22T21:16:49.489-03:00: You are running this process as the root user, which is not recommended
   2026-03-22T21:16:49.489-03:00: Soft rlimits for open file descriptors too low
   2026-03-22T21:16:49.489-03:00: For customers running the current memory allocator, we suggest changing the contents of the following sysfsFile
   2026-03-22T21:16:49.489-03:00: We suggest setting the contents of sysfsFile to 0.
   2026-03-22T21:16:49.489-03:00: Your system has glibc support for rseq built in, which is not yet supported by tcmalloc-google and has critical performance implications. Please set the environment variable GLIBC_TUNABLES=glibc.pthread.rseq=0
   2026-03-22T21:16:49.490-03:00: We suggest setting swappiness to 0 or 1, as swapping can cause performance problems.
------

Enterprise test> rsconf = {
|   _id: "rs0",
|   members: [
|     { _id: 0, host: "mongodbsrv:27017" },
|     { _id: 1, host: "mongodbsrv:27018" },
|     { _id: 2, host: "mongodbsrv:27019" }
|    ]
| }
{
  _id: 'rs0',
  members: [
    { _id: 0, host: 'mongodbsrv:27017' },
    { _id: 1, host: 'mongodbsrv:27018' },
    { _id: 2, host: 'mongodbsrv:27019' }
  ]
}
Enterprise test> rs.initiate( rsconf )
{
  ok: 1,
  '$clusterTime': {
    clusterTime: Timestamp({ t: 1774226586, i: 1 }),
    signature: {
      hash: Binary.createFromBase64('AAAAAAAAAAAAAAAAAAAAAAAAAAA=', 0),
      keyId: Long('0')
    }
  },
  operationTime: Timestamp({ t: 1774226586, i: 1 })
}
Enterprise rs0 [direct: secondary] test> rs.conf()
{
  _id: 'rs0',
  version: 1,
  term: 1,
  members: [
    {
      _id: 0,
      host: 'mongodbsrv:27017',
      arbiterOnly: false,
      buildIndexes: true,
      hidden: false,
      priority: 1,
      tags: {},
      secondaryDelaySecs: Long('0'),
      votes: 1
    },
    {
      _id: 1,
      host: 'mongodbsrv:27018',
      arbiterOnly: false,
      buildIndexes: true,
      hidden: false,
      priority: 1,
      tags: {},
      secondaryDelaySecs: Long('0'),
      votes: 1
    },
    {
      _id: 2,
      host: 'mongodbsrv:27019',
      arbiterOnly: false,
      buildIndexes: true,
      hidden: false,
      priority: 1,
      tags: {},
      secondaryDelaySecs: Long('0'),
      votes: 1
    }
  ],
  protocolVersion: Long('1'),
  writeConcernMajorityJournalDefault: true,
  settings: {
    chainingAllowed: true,
    heartbeatIntervalMillis: 2000,
    heartbeatTimeoutSecs: 10,
    electionTimeoutMillis: 10000,
    catchUpTimeoutMillis: -1,
    catchUpTakeoverDelayMillis: 30000,
    getLastErrorModes: {},
    getLastErrorDefaults: { w: 1, wtimeout: 0 },
    replicaSetId: ObjectId('69c08c9a3a7c8207c57cdb2a')
  }
}

To manage the stop and start service via systemd, we will stop the Mongodb instance and create services files:

[root@mongodbsrv ~]$ kill -9 14448 14632 14701
[root@mongodbsrv ~]$ ps -ef |grep mongod
pcp         2878       1  0 20:36 ?        00:00:00 /usr/bin/pmie -b -m pmie_check -F -P -l /var/log/pcp/pmie/mongodbsrv/pmie.log -c config.default
root       15843    8796  0 21:42 pts/0    00:00:00 grep --color=auto mongod
[root@mongodbsrv ~]$ cd /etc/systemd/system/
[root@mongodbsrv system]$ vim mongod_rs0-0.service
[Unit]
Description=Mongodb Service 0
After=network.target

[Service]
Type=forking
ExecStart=/usr/bin/mongod --config /etc/mongod_rs0-0.conf 

[Install]
WantedBy=multi-user.target

Lets create another 2 and modify each one the instances:

[root@mongodbsrv system]$ cp mongod_rs0-0.service mongod_rs0-1.service
[root@mongodbsrv system]$ cp mongod_rs0-0.service mongod_rs0-2.service
[root@mongodbsrv system]$ vim mongod_rs0-1.service
[Unit]
Description=Mongodb Service 1
After=network.target

[Service]
Type=forking
ExecStart=/usr/bin/mongod --config /etc/mongod_rs0-1.conf 

[Install]
WantedBy=multi-user.target
[root@mongodbsrv system]$ vim mongod_rs0-2.service
[Unit]
Description=Mongodb Service 2
After=network.target

[Service]
Type=forking
ExecStart=/usr/bin/mongod --config /etc/mongod_rs0-2.conf 

[Install]
WantedBy=multi-user.target
[root@mongodbsrv system]$

We need to reload the daemons and enable MongoDB services on systemd:

[root@mongodbsrv system]$ systemctl daemon-reload
[root@mongodbsrv system]$ systemctl enable mongod_rs0-0.service
Created symlink /etc/systemd/system/multi-user.target.wants/mongod_rs0-0.service → /etc/systemd/system/mongod_rs0-0.service.
[root@mongodbsrv system]$ systemctl enable mongod_rs0-1.service
Created symlink /etc/systemd/system/multi-user.target.wants/mongod_rs0-1.service → /etc/systemd/system/mongod_rs0-1.service.
[root@mongodbsrv system]$ systemctl enable mongod_rs0-2.service
Created symlink /etc/systemd/system/multi-user.target.wants/mongod_rs0-2.service → /etc/systemd/system/mongod_rs0-2.service.

Now, lets start the services:

[root@mongodbsrv system]$ systemctl start mongod_rs0-0.service
[root@mongodbsrv system]$ systemctl start mongod_rs0-1.service
[root@mongodbsrv system]$ systemctl start mongod_rs0-2.service
[root@mongodbsrv system]$ systemctl status mongod_rs0-0.service
● mongod_rs0-0.service - Mongodb Service 0
     Loaded: loaded (/etc/systemd/system/mongod_rs0-0.service; enabled; preset: disabled)
     Active: active (running) since Sun 2026-03-22 23:05:37 -03; 28s ago
    Process: 28722 ExecStart=/usr/bin/mongod --config /etc/mongod_rs0-0.conf (code=exited, status=0/SUCCESS)
   Main PID: 28724 (mongod)
      Tasks: 77 (limit: 22648)
     Memory: 215.7M (peak: 216.6M)
        CPU: 1.061s
     CGroup: /system.slice/mongod_rs0-0.service
             └─28724 /usr/bin/mongod --config /etc/mongod_rs0-0.conf

Mar 22 23:05:36 mongodbsrv systemd[1]: Starting Mongodb Service 0...
Mar 22 23:05:36 mongodbsrv mongod[28722]: about to fork child process, waiting until server is ready for connections.
Mar 22 23:05:36 mongodbsrv mongod[28724]: forked process: 28724
Mar 22 23:05:37 mongodbsrv mongod[28722]: child process started successfully, parent exiting
Mar 22 23:05:37 mongodbsrv systemd[1]: Started Mongodb Service 0.
[root@mongodbsrv system]$ systemctl status mongod_rs0-1.service
● mongod_rs0-1.service - Mongodb Service 1
     Loaded: loaded (/etc/systemd/system/mongod_rs0-1.service; enabled; preset: disabled)
     Active: active (running) since Sun 2026-03-22 23:07:15 -03; 10s ago
    Process: 28953 ExecStart=/usr/bin/mongod --config /etc/mongod_rs0-1.conf (code=exited, status=0/SUCCESS)
   Main PID: 28955 (mongod)
      Tasks: 82 (limit: 22648)
     Memory: 215.9M (peak: 216.7M)
        CPU: 766ms
     CGroup: /system.slice/mongod_rs0-1.service
             └─28955 /usr/bin/mongod --config /etc/mongod_rs0-1.conf

Mar 22 23:07:14 mongodbsrv systemd[1]: Starting Mongodb Service 1...
Mar 22 23:07:14 mongodbsrv mongod[28953]: about to fork child process, waiting until server is ready for connections.
Mar 22 23:07:14 mongodbsrv mongod[28955]: forked process: 28955
Mar 22 23:07:15 mongodbsrv mongod[28953]: child process started successfully, parent exiting
Mar 22 23:07:15 mongodbsrv systemd[1]: Started Mongodb Service 1.
[root@mongodbsrv system]$ systemctl status mongod_rs0-2.service
● mongod_rs0-2.service - Mongodb Service 2
     Loaded: loaded (/etc/systemd/system/mongod_rs0-2.service; enabled; preset: disabled)
     Active: active (running) since Sun 2026-03-22 23:07:18 -03; 11s ago
    Process: 29059 ExecStart=/usr/bin/mongod --config /etc/mongod_rs0-2.conf (code=exited, status=0/SUCCESS)
   Main PID: 29062 (mongod)
      Tasks: 96 (limit: 22648)
     Memory: 243.3M (peak: 244.0M)
        CPU: 806ms
     CGroup: /system.slice/mongod_rs0-2.service
             └─29062 /usr/bin/mongod --config /etc/mongod_rs0-2.conf

Mar 22 23:07:17 mongodbsrv systemd[1]: Starting Mongodb Service 2...
Mar 22 23:07:17 mongodbsrv mongod[29059]: about to fork child process, waiting until server is ready for connections.
Mar 22 23:07:17 mongodbsrv mongod[29062]: forked process: 29062
Mar 22 23:07:18 mongodbsrv mongod[29059]: child process started successfully, parent exiting
Mar 22 23:07:18 mongodbsrv systemd[1]: Started Mongodb Service 2.

Lets check the cluster status:

[root@mongodbsrv system]$ mongosh --port 27017
Current Mongosh Log ID:	69c0a0dc73310fd57559b253
Connecting to:		mongodb://127.0.0.1:27017/?directConnection=true&serverSelectionTimeoutMS=2000&appName=mongosh+2.8.1
Using MongoDB:		8.0.20
Using Mongosh:		2.8.1

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

------
   The server generated these startup warnings when booting
   2026-03-22T23:05:37.241-03:00: Access control is not enabled for the database. Read and write access to data and configuration is unrestricted
   2026-03-22T23:05:37.241-03:00: You are running this process as the root user, which is not recommended
   2026-03-22T23:05:37.241-03:00: Soft rlimits for open file descriptors too low
   2026-03-22T23:05:37.241-03:00: For customers running the current memory allocator, we suggest changing the contents of the following sysfsFile
   2026-03-22T23:05:37.241-03:00: We suggest setting the contents of sysfsFile to 0.
   2026-03-22T23:05:37.241-03:00: Your system has glibc support for rseq built in, which is not yet supported by tcmalloc-google and has critical performance implications. Please set the environment variable GLIBC_TUNABLES=glibc.pthread.rseq=0
   2026-03-22T23:05:37.241-03:00: We suggest setting swappiness to 0 or 1, as swapping can cause performance problems.
------

Enterprise rs0 [direct: primary] test> rs.status
[Function: status] AsyncFunction {
  apiVersions: [ 0, 0 ],
  returnsPromise: true,
  serverVersions: [ '0.0.0', '999.999.999' ],
  topologies: [ 'ReplSet', 'Standalone', 'Sharded', 'LoadBalanced' ],
  returnType: { type: 'unknown', attributes: {} },
  deprecated: false,
  platforms: [ 'Compass', 'Browser', 'CLI' ],
  isDirectShellCommand: false,
  acceptsRawInput: false,
  shellCommandCompleter: undefined,
  newShellCommandCompleter: undefined,
  help: [Function (anonymous)] Help
}
Enterprise rs0 [direct: primary] test> rs.status()
{
  set: 'rs0',
  date: ISODate('2026-03-23T02:09:49.581Z'),
  myState: 1,
  term: Long('4'),
  syncSourceHost: '',
  syncSourceId: -1,
  heartbeatIntervalMillis: Long('2000'),
  majorityVoteCount: 2,
  writeMajorityCount: 2,
  votingMembersCount: 3,
  writableVotingMembersCount: 3,
  optimes: {
    lastCommittedOpTime: { ts: Timestamp({ t: 1774231785, i: 1 }), t: Long('4') },
    lastCommittedWallTime: ISODate('2026-03-23T02:09:45.984Z'),
    readConcernMajorityOpTime: { ts: Timestamp({ t: 1774231785, i: 1 }), t: Long('4') },
    appliedOpTime: { ts: Timestamp({ t: 1774231785, i: 1 }), t: Long('4') },
    durableOpTime: { ts: Timestamp({ t: 1774231785, i: 1 }), t: Long('4') },
    writtenOpTime: { ts: Timestamp({ t: 1774231785, i: 1 }), t: Long('4') },
    lastAppliedWallTime: ISODate('2026-03-23T02:09:45.984Z'),
    lastDurableWallTime: ISODate('2026-03-23T02:09:45.984Z'),
    lastWrittenWallTime: ISODate('2026-03-23T02:09:45.984Z')
  },
  lastStableRecoveryTimestamp: Timestamp({ t: 1774231775, i: 1 }),
  electionCandidateMetrics: {
    lastElectionReason: 'electionTimeout',
    lastElectionDate: ISODate('2026-03-23T02:07:25.957Z'),
    electionTerm: Long('4'),
    lastCommittedOpTimeAtElection: { ts: Timestamp({ t: 0, i: 0 }), t: Long('-1') },
    lastSeenWrittenOpTimeAtElection: { ts: Timestamp({ t: 1774230581, i: 1 }), t: Long('3') },
    lastSeenOpTimeAtElection: { ts: Timestamp({ t: 1774230581, i: 1 }), t: Long('3') },
    numVotesNeeded: 2,
    priorityAtElection: 1,
    electionTimeoutMillis: Long('10000'),
    numCatchUpOps: Long('0'),
    newTermStartDate: ISODate('2026-03-23T02:07:25.968Z'),
    wMajorityWriteAvailabilityDate: ISODate('2026-03-23T02:07:25.973Z')
  },
  members: [
    {
      _id: 0,
      name: 'mongodbsrv:27017',
      health: 1,
      state: 1,
      stateStr: 'PRIMARY',
      uptime: 253,
      optime: { ts: Timestamp({ t: 1774231785, i: 1 }), t: Long('4') },
      optimeDate: ISODate('2026-03-23T02:09:45.000Z'),
      optimeWritten: { ts: Timestamp({ t: 1774231785, i: 1 }), t: Long('4') },
      optimeWrittenDate: ISODate('2026-03-23T02:09:45.000Z'),
      lastAppliedWallTime: ISODate('2026-03-23T02:09:45.984Z'),
      lastDurableWallTime: ISODate('2026-03-23T02:09:45.984Z'),
      lastWrittenWallTime: ISODate('2026-03-23T02:09:45.984Z'),
      syncSourceHost: '',
      syncSourceId: -1,
      infoMessage: '',
      electionTime: Timestamp({ t: 1774231645, i: 1 }),
      electionDate: ISODate('2026-03-23T02:07:25.000Z'),
      configVersion: 1,
      configTerm: 4,
      self: true,
      lastHeartbeatMessage: ''
    },
    {
      _id: 1,
      name: 'mongodbsrv:27018',
      health: 1,
      state: 2,
      stateStr: 'SECONDARY',
      uptime: 154,
      optime: { ts: Timestamp({ t: 1774231785, i: 1 }), t: Long('4') },
      optimeDurable: { ts: Timestamp({ t: 1774231785, i: 1 }), t: Long('4') },
      optimeWritten: { ts: Timestamp({ t: 1774231785, i: 1 }), t: Long('4') },
      optimeDate: ISODate('2026-03-23T02:09:45.000Z'),
      optimeDurableDate: ISODate('2026-03-23T02:09:45.000Z'),
      optimeWrittenDate: ISODate('2026-03-23T02:09:45.000Z'),
      lastAppliedWallTime: ISODate('2026-03-23T02:09:45.984Z'),
      lastDurableWallTime: ISODate('2026-03-23T02:09:45.984Z'),
      lastWrittenWallTime: ISODate('2026-03-23T02:09:45.984Z'),
      lastHeartbeat: ISODate('2026-03-23T02:09:48.024Z'),
      lastHeartbeatRecv: ISODate('2026-03-23T02:09:48.562Z'),
      pingMs: Long('0'),
      lastHeartbeatMessage: '',
      syncSourceHost: 'mongodbsrv:27017',
      syncSourceId: 0,
      infoMessage: '',
      configVersion: 1,
      configTerm: 4
    },
    {
      _id: 2,
      name: 'mongodbsrv:27019',
      health: 1,
      state: 2,
      stateStr: 'SECONDARY',
      uptime: 151,
      optime: { ts: Timestamp({ t: 1774231785, i: 1 }), t: Long('4') },
      optimeDurable: { ts: Timestamp({ t: 1774231785, i: 1 }), t: Long('4') },
      optimeWritten: { ts: Timestamp({ t: 1774231785, i: 1 }), t: Long('4') },
      optimeDate: ISODate('2026-03-23T02:09:45.000Z'),
      optimeDurableDate: ISODate('2026-03-23T02:09:45.000Z'),
      optimeWrittenDate: ISODate('2026-03-23T02:09:45.000Z'),
      lastAppliedWallTime: ISODate('2026-03-23T02:09:45.984Z'),
      lastDurableWallTime: ISODate('2026-03-23T02:09:45.984Z'),
      lastWrittenWallTime: ISODate('2026-03-23T02:09:45.984Z'),
      lastHeartbeat: ISODate('2026-03-23T02:09:48.024Z'),
      lastHeartbeatRecv: ISODate('2026-03-23T02:09:48.562Z'),
      pingMs: Long('0'),
      lastHeartbeatMessage: '',
      syncSourceHost: 'mongodbsrv:27017',
      syncSourceId: 0,
      infoMessage: '',
      configVersion: 1,
      configTerm: 4
    }
  ],
  ok: 1,
  '$clusterTime': {
    clusterTime: Timestamp({ t: 1774231785, i: 1 }),
    signature: {
      hash: Binary.createFromBase64('AAAAAAAAAAAAAAAAAAAAAAAAAAA=', 0),
      keyId: Long('0')
    }
  },
  operationTime: Timestamp({ t: 1774231785, i: 1 })
}

That’s it.

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