Lesson 7: Configuring a Replica Set in a MongoDB Deployment / Learn
Code Summary: Configuring a Replica Set in a MongoDB Deployment
Review the following code, which demonstrates how to:
- Retrieve the status of a
mongodinstance - Reconfigure a running replica set
- Set the priority of a replica set
- Add and remove members of a replica set
- Retrieve the status of a replica set
Retrieve the Status of a mongod Instance
Use the db.hello() command to retrieve information about a replica set, including:
- The host of each member
- The name of the replica set
- The name of the primary
- The election id
- The timestamps for when the last operation occurred and when it became durable
Here’s an example of the output:
{
topologyVersion: {
processId: ObjectId("63fd0cd9a301ea9f0b1049d2"),
counter: Long("6")
},
hosts: [
'mongod0.replset.com:27017',
'mongod1.replset.com:27017',
'mongod2.replset.com:27017'
],
setName: 'mongodb-repl-example',
setVersion: 1,
isWritablePrimary: true,
secondary: false,
primary: 'mongod0.replset.com:27017',
me: 'mongod0.replset.com:27017',
electionId: ObjectId("7fffffff0000000000000003"),
lastWrite: {
opTime: { ts: Timestamp({ t: 1675469681, i: 1 }), t: Long("3") },
lastWriteDate: ISODate("2023-02-04T00:14:41.000Z"),
majorityOpTime: { ts: Timestamp({ t: 1675469681, i: 1 }), t: Long("3") },
majorityWriteDate: ISODate("2023-02-04T00:14:41.000Z")
},
maxBsonObjectSize: 16777216,
maxMessageSizeBytes: 48000000,
maxWriteBatchSize: 100000,
localTime: ISODate("2023-02-04T00:14:44.847Z"),
logicalSessionTimeoutMinutes: 30,
connectionId: 130,
minWireVersion: 0,
maxWireVersion: 17,
readOnly: false,
ok: 1,
'$clusterTime': {
clusterTime: Timestamp({ t: 1677542950, i: 6 }),
signature: {
hash: Binary(Buffer.from("fac842d36ee350c41d1aa908ba6d306f53afc514", "hex"), 0),
keyId: Long("7148911878087901206")
}
},
operationTime: Timestamp({ t: 1677542950, i: 6 })
}
Reconfigure a Running Replica Set
To reconfigure a running replica set, use rs.conf(). Assign the rs.conf() command to a variable to retrieve the replica set configuration object:
config = rs.conf()
Set the Priority of a Replica Set
Set the priority of a replica set by assigning a priority value for each member. For example:
config.members[2].priority = 10
Add a Member to a Replica Set
To add a new member to a replica set, define the new member’s _id and host name in an object. Then, push this new member to the members array in the configuration object. Here’s an example:
member = {"_id": 3, "host": "mongod3.replset.com:27017"}
config.members.push(member)
Alternatively, you can use the rs.add() wrapper followed by the host to add a member to the replica set. For example:
rs.add("mongod3.replset.com:27017")
Remove a Member from a Replica Set
To remove a member from a replica set, use the JavaScript splice() method. Pass in as arguments the index of the starting member and the number of elements being removed:
config.members.splice(1, 1)
Alternatively, you can use the rs.remove() wrapper followed by the host to remove a member from the replica set:
rs.remove("mongod1.replset.com:27017")
To apply the changes, use the rs.reconfig() command, passing in the config variable as an argument. For example:
rs.reconfig(config)
Retrieve the Status of a Replica Set
Use the db.status() command to retrieve the current status of a replica set, such as:
- The health of each member
- Whether a member is the primary or a secondary
- Information about operations
Note that this is not an exhaustive list. Here’s an example of output from the db.status() command:
{
set: 'mongodb-repl-example',
date: ISODate("2023-02-28T00:41:35.813Z"),
myState: 1,
term: Long("2"),
syncSourceHost: '',
syncSourceId: -1,
heartbeatIntervalMillis: Long("2000"),
majorityVoteCount: 2,
writeMajorityCount: 2,
votingMembersCount: 3,
writableVotingMembersCount: 3,
optimes: {
lastCommittedOpTime: { ts: Timestamp({ t: 1677544891, i: 1 }), t: Long("2") },
lastCommittedWallTime: ISODate("2023-02-28T00:41:31.541Z"),
readConcernMajorityOpTime: { ts: Timestamp({ t: 1677544891, i: 1 }), t: Long("2") },
appliedOpTime: { ts: Timestamp({ t: 1677544891, i: 1 }), t: Long("2") },
durableOpTime: { ts: Timestamp({ t: 1677544891, i: 1 }), t: Long("2") },
lastAppliedWallTime: ISODate("2023-02-28T00:41:31.541Z"),
lastDurableWallTime: ISODate("2023-02-28T00:41:31.541Z")
},
lastStableRecoveryTimestamp: Timestamp({ t: 1677544861, i: 1 }),
electionCandidateMetrics: {
lastElectionReason: 'priorityTakeover',
lastElectionDate: ISODate("2023-02-24T00:51:51.911Z"),
electionTerm: Long("2"),
lastCommittedOpTimeAtElection: { ts: Timestamp({ t: 1677199900, i: 1 }), t: Long("1") },
lastSeenOpTimeAtElection: { ts: Timestamp({ t: 1677199900, i: 1 }), t: Long("1") },
numVotesNeeded: 2,
priorityAtElection: 10,
electionTimeoutMillis: Long("10000"),
priorPrimaryMemberId: 0,
numCatchUpOps: Long("0"),
newTermStartDate: ISODate("2023-02-24T00:51:52.276Z"),
wMajorityWriteAvailabilityDate: ISODate("2023-02-24T00:51:53.386Z")
},
electionParticipantMetrics: {
votedForCandidate: true,
electionTerm: Long("1"),
lastVoteDate: ISODate("2023-02-23T22:55:27.165Z"),
electionCandidateMemberId: 0,
voteReason: '',
lastAppliedOpTimeAtElection: { ts: Timestamp({ t: 1677192915, i: 1 }), t: Long("-1") },
maxAppliedOpTimeInSet: { ts: Timestamp({ t: 1677192915, i: 1 }), t: Long("-1") },
priorityAtElection: 1
},
members: [
{
_id: 0,
name: 'mongodb.repl.member.one:27017',
health: 1,
state: 2,
stateStr: 'SECONDARY',
uptime: 351979,
optime: { ts: Timestamp({ t: 1677544891, i: 1 }), t: Long("2") },
optimeDurable: { ts: Timestamp({ t: 1677544891, i: 1 }), t: Long("2") },
optimeDate: ISODate("2023-02-28T00:41:31.000Z"),
optimeDurableDate: ISODate("2023-02-28T00:41:31.000Z"),
lastAppliedWallTime: ISODate("2023-02-28T00:41:31.541Z"),
lastDurableWallTime: ISODate("2023-02-28T00:41:31.541Z"),
lastHeartbeat: ISODate("2023-02-28T00:41:34.484Z"),
lastHeartbeatRecv: ISODate("2023-02-28T00:41:35.787Z"),
pingMs: Long("37"),
lastHeartbeatMessage: '',
syncSourceHost: 'mongodb.repl.member.three:27017',
syncSourceId: 2,
infoMessage: '',
configVersion: 5,
configTerm: 2
},
{
_id: 2,
name: 'mongodb.repl.member.three:27017',
health: 1,
state: 1,
stateStr: 'PRIMARY',
uptime: 352657,
optime: { ts: Timestamp({ t: 1677544891, i: 1 }), t: Long("2") },
optimeDate: ISODate("2023-02-28T00:41:31.000Z"),
lastAppliedWallTime: ISODate("2023-02-28T00:41:31.541Z"),
lastDurableWallTime: ISODate("2023-02-28T00:41:31.541Z"),
syncSourceHost: '',
syncSourceId: -1,
infoMessage: '',
electionTime: Timestamp({ t: 1677199911, i: 1 }),
electionDate: ISODate("2023-02-24T00:51:51.000Z"),
configVersion: 5,
configTerm: 2,
self: true,
lastHeartbeatMessage: ''
},
{
_id: 3,
name: 'mongodb.repl.member.two:27017',
health: 1,
state: 2,
stateStr: 'SECONDARY',
uptime: 343537,
optime: { ts: Timestamp({ t: 1677544891, i: 1 }), t: Long("2") },
optimeDurable: { ts: Timestamp({ t: 1677544891, i: 1 }), t: Long("2") },
optimeDate: ISODate("2023-02-28T00:41:31.000Z"),
optimeDurableDate: ISODate("2023-02-28T00:41:31.000Z"),
lastAppliedWallTime: ISODate("2023-02-28T00:41:31.541Z"),
lastDurableWallTime: ISODate("2023-02-28T00:41:31.541Z"),
lastHeartbeat: ISODate("2023-02-28T00:41:34.720Z"),
lastHeartbeatRecv: ISODate("2023-02-28T00:41:34.206Z"),
pingMs: Long("62"),
lastHeartbeatMessage: '',
syncSourceHost: 'mongodb.repl.member.one:27017',
syncSourceId: 0,
infoMessage: '',
configVersion: 5,
configTerm: 2
}
],
ok: 1,
'$clusterTime': {
clusterTime: Timestamp({ t: 1677544891, i: 1 }),
signature: {
hash: Binary(Buffer.from("65e1e3e9636a54a0af40f152c7f2f061466096a3", "hex"), 0),
keyId: Long("7203488770547515397")
}
},
operationTime: Timestamp({ t: 1677544891, i: 1 })
}