dimanche 10 octobre 2021
mercredi 6 octobre 2021
MongoDB High Availability Cluster Implementation Part 2
MongoDB
High Availability Cluster
Part
2
Replication and Sharding Implementation
By
Donatien MBADI OUM, Database Expert
1. Introduction
In part 1 we presented an Overview of MongoDB High
Availability. The goal of this second part is to be practice by implementing
replication and sharding. On this case, all the MongoDB instances are hosted on
a Linux machine. In real case, separated servers are used with different Ips
addresses.
We will start by setting up our replication by using the following steps:
-
Creating appropriated folders for each MongoDB instance
-
Starting the mongod instances
-
Enabling replication in MongoDB
-
Adding MongoDB instances to replica set
-
Testing the replication process
-
Testing the failover
-
Removing MongoDB instance from replica set
After that we will implement our sharding by following the below steps:
-
Creating
Config Servers for MongoDB
-
Creating
Shard Servers for MongoDB
-
Starting
the Servers to initiate MongoDB Replication
-
Adding
Shards to MongoDB Shard Servers
-
Testing
the Sharding process
2. Configuring
MongoDB Replication
2.1.
Environment
On this tutorial, we are using:
- Oracle VirtualBox 6.1
- Enterprise Linux 8.4
- MongoDB 5.0
2.2.
Architecture
On this tutorial, we create 5 instances
for replication as below:
- One master instance
- Three secondaries’ instances
- An arbiter
2.3.
Creating instance folders
Since we are using a same machine (In
real case, we should have different servers), we create 5 directories, one for
each instance:
/opt/data/repl01/inst01
/opt/data/repl01/inst02
/opt/data/repl01/inst03
/opt/data/repl01/inst04
/opt/data/repl01/arbiter
2.4.
Starting MongoDB instance
We choose repl01 as a name of our
replicat set. To start the mongod instance, we specify the port value for the
Mongo instance along with the path to our MongoDB installation. For each
instance, we will add shardsrv option to prepare a future sharding
configuration in a partitioned cluster.
To start the instances, we have can
either directly running the mongod with all the options you need or by
configuring a configuration file.
We choose the following command to
enable the first mongod instance:
mongod --replSet repl01 --journal --port
27101 --shardsvr --dbpath /opt/data/repl01/inst01 --logpath /opt/data/repl01/inst01/mongod_27101.log
--fork
To use the configuration file, we need
to first copy the existing sample file /etc/mongod.conf.
Eg. For instance inst01 (shard server),
cp /etc/mongod.conf /etc/confs/repl01/inst01/mongod_inst01.conf
#vim /etc/confs/repl01/inst01/mongod_inst01.conf
#
mongod.conf
# for
documentation of all options, see:
#
http://docs.mongodb.org/manual/reference/configuration-options/
# where
to write logging data.
systemLog:
destination: file
logAppend: true
path:
/opt/data/repl01/inst01/mongod_27101.log
# Where
and how to store data.
storage:
dbPath: /opt/data/repl01/inst01
journal:
enabled: true
# engine:
# wiredTiger:
# how
the process runs
processManagement:
fork: true
# fork and run in background
pidFilePath: /var/run/mongodb/mongod.pid # location of pidfile
timeZoneInfo: /usr/share/zoneinfo
#
network interfaces
net:
port: 27101
bindIp: 127.0.0.1 # Enter 0.0.0.0,:: to bind to all IPv4 and
IPv6 addresses or, alternatively, use the net.bindIpAll setting.
#security:
#operationProfiling:
replication:
replSetName: "repl01"
sharding:
clusterRole: shardsvr
##
Enterprise-Only Options
#auditLog:
#snmp:
We also create the other instances
including the arbiter:
[root@linuxsvr01]# mongod --replSet repl01 --journal --port 27102
--shardsvr --dbpath /opt/data/repl01/inst02 --logpath /opt/data/repl01/inst01/mongod_27102.log
--fork
about to fork child process, waiting until server is ready for
connections.
forked process: 9704
child process started successfully, parent exiting
[root@linuxsvr01]# mongod --replSet repl01 --journal --port 27103
--shardsvr --dbpath /opt/data/repl01/inst03 --logpath /opt/data/repl01/inst03/mongod_27103.log
--fork
about to fork child process, waiting until server is ready for
connections.
forked process: 9760
child process started successfully, parent exiting
[root@linuxsvr01]#
[root@linuxsvr01 inst01]# mongod --replSet repl01 --journal --port 27104
--shardsvr --dbpath /opt/data/repl01/inst04 --logpath /opt/data/repl01/inst04/mongod_27104.log
--fork
about to fork child process, waiting until server is ready for
connections.
forked process: 9817
child process started successfully, parent exiting
[root@linuxsvr01]# mongod --replSet repl01 --journal --port 27100
--shardsvr --dbpath /opt/data/repl01/arbiter --logpath /opt/data/repl01/inst01/mongod_27100.log
--fork
about to fork child process, waiting until server is ready for
connections.
forked process: 9871
child process started successfully, parent exiting
[root@linuxsvr01]#
Or by using a configuration file for
each instance:
2.5.
Enabling replication
On your production environment, you must
make Ips/Host name configurations on /etc/host files on each server.
Now, we need to open the Mongo Shell
with our primary instance as follows:
[root@linuxsvr01]# mongosh --port 27101
Note: We can still use mongo --port in MongoDB 5.0, but the new shell is mongosh
--port is deprecated.
After connected on the first instance,
we need to initiate the replication as follow:
test>
use admin
switched
to db admin
admin>
admin>
cfg={_id:"repl01",members:[{_id:0,host:"127.0.0.1:27101"},{_id:1,host:"127.0.0.1:27102"},{_id:2,host:"127.0.0.1:27100",arbiterOnly:true}]}
{
_id: 'repl01',
members: [
{ _id: 0, host: '127.0.0.1:27101' },
{ _id: 1, host: '127.0.0.1:27102' },
{
_id: 2, host: '127.0.0.1:27100', arbiterOnly: true }
]
}
admin>
admin>
rs.initiate(cfg);
{ ok: 1
}
repl01
[direct: other] admin>
repl01
[direct: secondary] admin>
2.6.
Adding nodes on replica set
Once we have initialized our Replica
Set, we can now add the various MongoDB instances using the add command as
follows:
>rs.add('127.0.0.1:27103')
The output {‘ok’:1} indicates that a MongoDB instance has
been successfully added to the Replica Set.
Note: We can also add an arbiter as
follow:
repl01:PRIMARY> rs.addArb('127.0.0.1:27100')
To check the status of the replication,
you can use the status command as follows:
>rs.status
repl01
[direct: primary] admin> rs.status()
{
set: 'repl01',
date:
ISODate("2021-09-23T22:33:51.584Z"),
myState: 1,
term: Long("1"),
syncSourceHost: '',
syncSourceId: -1,
heartbeatIntervalMillis:
Long("2000"),
majorityVoteCount: 3,
writeMajorityCount: 3,
votingMembersCount: 5,
writableVotingMembersCount: 4,
optimes: {
lastCommittedOpTime: { ts: Timestamp({ t:
1632436430, i: 1 }), t: Long("1") },
lastCommittedWallTime:
ISODate("2021-09-23T22:33:50.123Z"),
readConcernMajorityOpTime: { ts:
Timestamp({ t: 1632436430, i: 1 }), t: Long("1") },
appliedOpTime: { ts: Timestamp({ t:
1632436430, i: 1 }), t: Long("1") },
durableOpTime: { ts: Timestamp({ t:
1632436430, i: 1 }), t: Long("1") },
lastAppliedWallTime:
ISODate("2021-09-23T22:33:50.123Z"),
lastDurableWallTime:
ISODate("2021-09-23T22:33:50.123Z")
},
lastStableRecoveryTimestamp: Timestamp({ t:
1632436370, i: 1 }),
electionCandidateMetrics: {
lastElectionReason: 'electionTimeout',
lastElectionDate:
ISODate("2021-09-23T22:16:49.982Z"),
electionTerm: Long("1"),
lastCommittedOpTimeAtElection: { ts:
Timestamp({ t: 0, i: 0 }), t: Long("-1") },
lastSeenOpTimeAtElection: { ts: Timestamp({
t: 1632435398, i: 1 }), t: Long("-1") },
numVotesNeeded: 2,
priorityAtElection: 1,
electionTimeoutMillis:
Long("10000"),
numCatchUpOps: Long("0"),
newTermStartDate:
ISODate("2021-09-23T22:16:50.069Z"),
wMajorityWriteAvailabilityDate:
ISODate("2021-09-23T22:16:50.718Z")
},
members: [
{
_id: 0,
name: '127.0.0.1:27101',
health: 1,
state: 1,
stateStr: 'PRIMARY',
uptime: 3700,
optime: { ts: Timestamp({ t: 1632436430,
i: 1 }), t: Long("1") },
optimeDate:
ISODate("2021-09-23T22:33:50.000Z"),
syncSourceHost: '',
syncSourceId: -1,
infoMessage: '',
electionTime: Timestamp({ t: 1632435410,
i: 1 }),
electionDate:
ISODate("2021-09-23T22:16:50.000Z"),
configVersion: 3,
configTerm: 1,
self: true,
lastHeartbeatMessage: ''
},
{
_id: 1,
name: '127.0.0.1:27102',
health: 1,
state: 2,
stateStr: 'SECONDARY',
uptime: 1032,
optime: { ts: Timestamp({ t: 1632436430,
i: 1 }), t: Long("1") },
optimeDurable: { ts: Timestamp({ t:
1632436430, i: 1 }), t: Long("1") },
optimeDate:
ISODate("2021-09-23T22:33:50.000Z"),
optimeDurableDate:
ISODate("2021-09-23T22:33:50.000Z"),
lastHeartbeat: ISODate("2021-09-23T22:33:50.180Z"),
lastHeartbeatRecv:
ISODate("2021-09-23T22:33:50.174Z"),
pingMs: Long("0"),
lastHeartbeatMessage: '',
syncSourceHost: '127.0.0.1:27101',
syncSourceId: 0,
infoMessage: '',
configVersion: 3,
configTerm: 1
},
{
_id: 2,
name: '127.0.0.1:27100',
health: 1,
state: 7,
stateStr: 'ARBITER',
uptime: 1032,
lastHeartbeat:
ISODate("2021-09-23T22:33:50.180Z"),
lastHeartbeatRecv:
ISODate("2021-09-23T22:33:50.174Z"),
pingMs: Long("0"),
lastHeartbeatMessage: '',
syncSourceHost: '',
syncSourceId: -1,
infoMessage: '',
configVersion: 3,
configTerm: 1
},
{
_id: 3,
name: '127.0.0.1:27103',
health: 1,
state: 2,
stateStr: 'SECONDARY',
uptime: 173,
optime: { ts: Timestamp({ t: 1632436430,
i: 1 }), t: Long("1") },
optimeDurable: { ts: Timestamp({ t:
1632436430, i: 1 }), t: Long("1") },
optimeDate:
ISODate("2021-09-23T22:33:50.000Z"),
optimeDurableDate:
ISODate("2021-09-23T22:33:50.000Z"),
lastHeartbeat:
ISODate("2021-09-23T22:33:50.180Z"),
lastHeartbeatRecv:
ISODate("2021-09-23T22:33:51.172Z"),
pingMs: Long("0"),
lastHeartbeatMessage: '',
syncSourceHost: '127.0.0.1:27102',
syncSourceId: 1,
infoMessage: '',
configVersion: 3,
configTerm: 1
},
{
_id: 4,
name: '127.0.0.1:27104',
health: 1,
state: 2,
stateStr: 'SECONDARY',
uptime: 163,
optime: { ts: Timestamp({ t: 1632436430,
i: 1 }), t: Long("1") },
optimeDurable: { ts: Timestamp({ t:
1632436430, i: 1 }), t: Long("1") },
optimeDate:
ISODate("2021-09-23T22:33:50.000Z"),
optimeDurableDate:
ISODate("2021-09-23T22:33:50.000Z"),
lastHeartbeat:
ISODate("2021-09-23T22:33:50.180Z"),
lastHeartbeatRecv:
ISODate("2021-09-23T22:33:51.374Z"),
pingMs: Long("0"),
lastHeartbeatMessage: '',
syncSourceHost: '127.0.0.1:27103',
syncSourceId: 3,
infoMessage: '',
configVersion: 3,
configTerm: 1
}
],
ok: 1,
'$clusterTime': {
clusterTime: Timestamp({ t: 1632436430, i:
1 }),
signature: {
hash:
Binary(Buffer.from("0000000000000000000000000000000000000000",
"hex"), 0),
keyId: Long("0")
}
},
operationTime: Timestamp({ t: 1632436430, i:
1 })
}
repl01
[direct: primary] admin>
We can also see which is the PRIMARY or
MASTER instance in our replication as follows:
>rs.isMaster()
2.7.
Testing the Replication Process
Now, we can test the process by adding a
document in the primary node. If replication is working properly, the document
will automatically be copied into the secondaries node.
We will add the below documents on
compta database:
{idclient:567, nomclient:"YAYA
Moussa", adresse:"Boulevard Amadou Ahidjo",
telephone:"67785-3390"},
{idclient:560, nomclient:"MBADI
Donatien", adresse:"Mbanga Japoma",
telephone:"67000-0000"},
{idclient:356, nomclient:"ONANA Brice
Roland",Ville:"Mbalmayo", telephone:"67785-3390"},
{idclient:580, nomclient:"SANTOUNGA
Yves-Cesaire", adresse:"Brescia Italie"},
{idclient:866,
nomclient:"YENE Yves-Evann", Pays:"Cameroun",
Contact:"MBADI OUM"}
First, connect to the primary node and
add a document using the insertMany command as follows:
repl01 [direct: primary] admin> use compta
switched to db compta
repl01 [direct: primary] compta>
db.clients.insertMany([{idclient:567, nomclient:"YAYA Moussa", adresse:"Boulevard
Amadou Ahidjo", telephone:"67785-3390"},
...
{idclient:560, nomclient:"MBADI Donatien",
adresse:"Mbanga Japoma", telephone:"67000-0000"},
... {idclient:356,
nomclient:"ONANA Brice Roland",Ville:"Mbalmayo",
telephone:"67785-3390"},
...
{idclient:580, nomclient:"SANTOUNGA Yves-Cesaire",
adresse:"Brescia Italie"},
...
{idclient:866, nomclient:"YENE Yves-Evann",
Pays:"Cameroun", Contact:"MBADI OUM"}
... ]);
{
acknowledged: true,
insertedIds: {
'0':
ObjectId("614d062cf545c64ecc90d9a0"),
'1':
ObjectId("614d062cf545c64ecc90d9a1"),
'2':
ObjectId("614d062cf545c64ecc90d9a2"),
'3':
ObjectId("614d062cf545c64ecc90d9a3"),
'4': ObjectId("614d062cf545c64ecc90d9a4")
}
}
repl01 [direct: primary] compta>
We can display documents as follow:
Now, we can switch to any secondary node
using the following command:
E.g: mongosh --port
27103
Once connected on a secondary node, we
try to display documents on clients collection:
We notice that, since we are connected
on a secondary node, we cannot display information because of error 13435.
We can allow a secondary node to accept
reads by running db.getMongo().setReadPref('secondary') in a mongo shell that is connected to
that secondary node. Allowing reads from a secondary is not recommended,
because you could be reading stale data if the node isn't yet synced with the
primary node.
2.8.
Removing node from replica set
MongoDB Replica Sets also allow users to
remove single or multiple instances they’ve added to the replica set using the
remove command. To remove a particular instance, we first need to shut it down.
Example: We need to remove instance
running on port 27104:
[root@linuxsvr01 ~]# mongo --port 27104
Current Mongosh Log ID: 614d0fd44520fc023111d647
Connecting to: mongodb://127.0.0.1:27104/?directConnection=true&serverSelectionTimeoutMS=2000
Using MongoDB: 5.0.2
Using Mongosh: 1.0.5
For mongosh info see: https://docs.mongodb.com/mongodb-shell/
------
The server generated these
startup warnings when booting:
2021-09-23T17:47:12.123-04:00:
Using the XFS filesystem is strongly recommended with the WiredTiger storage
engine. See http://dochub.mongodb.org/core/prodnotes-filesystem
2021-09-23T17:47:12.659-04:00:
Access control is not enabled for the database. Read and write access to data
and configuration is unrestricted
2021-09-23T17:47:12.659-04:00:
You are running this process as the root user, which is not recommended
2021-09-23T17:47:12.659-04:00:
/sys/kernel/mm/transparent_hugepage/enabled is 'always'. We suggest setting it
to 'never'
2021-09-23T17:47:12.659-04:00:
Soft rlimits for open file descriptors too low
------
Warning: Found ~/.mongorc.js, but not ~/.mongoshrc.js. ~/.mongorc.js
will not be loaded.
You may want to copy or rename
~/.mongorc.js to ~/.mongoshrc.js.
repl01 [direct: secondary] test>
repl01 [direct: secondary] test>
repl01:SECONDARY> use admin
switched to db admin
repl01:SECONDARY> db.shutdownServer()
MongoNetworkError: connection 3 to 127.0.0.1:27104
closedrepl01:SECONDARY>
Once we have shut down the server, we
need to connect with our primary server and use the remove command as follow:
repl01 [direct: primary]
admin> rs.remove('127.0.0.1:27104')
{
ok: 1,
'$clusterTime': {
clusterTime: Timestamp({ t: 1632440665, i:
1 }),
signature: {
hash:
Binary(Buffer.from("0000000000000000000000000000000000000000",
"hex"), 0),
keyId: Long("0")
}
},
operationTime: Timestamp({ t: 1632440665, i:
1 })
}
repl01 [direct: primary]
admin>}
After remove the instance, we can run
the command rs.isMaster() to check the instance roles.
2.9.
Testing the failover
This exercise consists of simulate the loss
of PRIMARY instance and then see what happens concerning the remaining nodes.
Let’s first add the node that we removed
and then display the status of our replica set using rs.status():
As we can see, the PRIMARY instance is
running on port 27101.
So, we will shut down the primary
instance by killing the mongod process which is running instance 1.
The former primary instance is now down.
Let’s connect to any other node and check which one is the new primary.
We can see that the new PRIMARY instance
is running on port 27103.
Let’s restart the former primary
instance and see the new status.
The instance which running on 27101 is
now turned as SECONDARY instance.
2.10. Force a member to
be Primary by Setting its Priority High
You can force a replica
set member to become primary by giving it a higher members[n].priority value than any other member in the
set.
Optionally, you also can force a member
never to become primary by setting its members[n].priority value to 0, which means the member can never seek election as primary.
This procedure assumes the below
configuration (This is part of rs.status command output):
…
…
members:
[
{
_id: 0,
name:
'127.0.0.1:27101',
health: 1,
state: 2,
stateStr: 'SECONDARY',
…
…
},
{
_id: 1,
name: '127.0.0.1:27102',
health: 1,
state: 1,
stateStr: 'PRIMARY',
…
…
{
_id: 2,
name: '127.0.0.1:27100',
health: 1,
state: 7,
stateStr: 'ARBITER',
},
{
_id: 3,
name: '127.0.0.1:27103',
health: 1,
state: 2,
stateStr: 'SECONDARY',
},
{
_id: 4,
name: '127.0.0.1:27104',
health: 1,
state: 2,
stateStr: 'SECONDARY',
}
]
…
…
The procedure assumes that
127.0.0.1/27102 is the actual primary node. We need to make 127.0.0.1/101 to be
the primary node.
We have four members and one arbiter. In
a mongosh session that is connected to the
primary 127.0.0.1/27102, we use the following sequence of operations to make 127.0.0.1/27101
the primary:
cfg =
rs.conf()
cfg.members[0].priority = 1
cfg.members[1].priority
= 0.5
cfg.members[2].priority
= 0 --Arbiter
cfg.members[3].priority
= 0.5
cfg.members[4].priority
= 0.5
rs.reconfig(cfg)
By running rs.status command we have the below:
…
…
members: [
{
_id: 0,
name: '127.0.0.1:27101',
health: 1,
state: 1,
stateStr: 'PRIMARY',
…
…
},
{
_id: 1,
name: '127.0.0.1:27102',
health: 1,
state: 2,
stateStr: 'SECONDARY',
…
…
},
{
_id: 2,
name: '127.0.0.1:27100',
health: 1,
state: 7,
stateStr: 'ARBITER',
…
…
},
{
_id: 3,
name: '127.0.0.1:27103',
health: 1,
state: 2,
stateStr: 'SECONDARY',
…
…
},
{
_id: 4,
name: '127.0.0.1:27104',
health: 1,
state: 2,
stateStr: 'SECONDARY',
…
…
}
],
ok: 1,
…
…
repl01
[direct: secondary] test> cfg=rs.conf()
{
_id: 'repl01',
version: 7,
term: 6,
members: [
{
_id: 0,
host: '127.0.0.1:27101',
arbiterOnly: false,
buildIndexes: true,
hidden: false,
priority: 1,
tags: {},
slaveDelay: Long("0"),
votes: 1
},
{
_id: 1,
host: '127.0.0.1:27102',
arbiterOnly: false,
buildIndexes: true,
hidden: false,
priority: 0.5,
tags: {},
slaveDelay: Long("0"),
votes: 1
},
{
_id: 2,
host: '127.0.0.1:27100',
arbiterOnly: true,
buildIndexes: true,
hidden: false,
priority: 0,
tags: {},
slaveDelay: Long("0"),
votes: 1
},
{
_id: 3,
host: '127.0.0.1:27103',
arbiterOnly: false,
buildIndexes: true,
hidden: false,
priority: 0.5,
tags: {},
slaveDelay: Long("0"),
votes: 1
},
{
_id: 4,
host: '127.0.0.1:27104',
arbiterOnly: false,
buildIndexes: true,
hidden: false,
priority: 0.5,
tags: {},
slaveDelay: 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("614cfcc67db73190be7daa50")
}
}
repl01
[direct: secondary] test>
3. Configuring
MongoDB Sharding
3.1.
Why sharding
In replication,
- all writes go to master node
- Latency sensitive queries still go to
master
- Single replica set has limitation of 12
nodes
- Memory can't be large enough when active
dataset is big
- Local disk is not big enough
- Vertical scaling is too expensive
3.2.
Architecture
On this tutorial, we consider the former
replica set with:
- One master instance
- Three secondaries’ instances
- An arbiter
Now, we will create:
- One replicat set with three config
instances
- One mongos instance
- An additional replicat set with one
master and two secondary nodes.
3.3.
Creation of a replicat set with config
servers
To achieve that, we will follow steps as
below:
- Create directories for config server
replica set
mkdir -p /opt/data/replcfg/ instcfg01
mkdir -p /opt/data/replcfg/ instcfg02
mkdir -p /opt/data/replcfg/ instcfg03
- Creation of config server instances
The configuration file for the config
server is as follow:
We start the config instances using
mongod:
- Initiation of config server replication
[root@linuxsvr01
replcfg]# mongosh --port 27201
Current
Mongosh Log ID: 6153e9ac7b64256f746b9c2e
Connecting
to:
mongodb://127.0.0.1:27201/?directConnection=true&serverSelectionTimeoutMS=2000
Using
MongoDB: 5.0.2
Using
Mongosh: 1.0.5
For
mongosh info see: https://docs.mongodb.com/mongodb-shell/
------
The server generated these startup warnings
when booting:
2021-09-29T00:00:13.882-04:00: Using the XFS
filesystem is strongly recommended with the WiredTiger storage engine. See
http://dochub.mongodb.org/core/prodnotes-filesystem
2021-09-29T00:00:14.846-04:00: Access
control is not enabled for the database. Read and write access to data and
configuration is unrestricted
2021-09-29T00:00:14.846-04:00: You are
running this process as the root user, which is not recommended
2021-09-29T00:00:14.846-04:00:
/sys/kernel/mm/transparent_hugepage/enabled is 'always'. We suggest setting it
to 'never'
2021-09-29T00:00:14.846-04:00: Soft rlimits
for open file descriptors too low
------
Warning:
Found ~/.mongorc.js, but not ~/.mongoshrc.js. ~/.mongorc.js will not be loaded.
You may want to copy or rename ~/.mongorc.js
to ~/.mongoshrc.js.
replcfg01
[direct: primary] test>
3.4.
Creation of mongos instance
Mongos instances is also called router
instances. They are basically mongo instances, interface with client
applications and direct operations to the appropriate shard. The query router
processes and targets the operations to shards and then returns results to the
clients. A sharded cluster can contain more than one query router to divide the
client request load. A client sends requests to one query router. Generally, a
sharded cluster have many query routers.
Now, we start the mongos instance using
the config servers created above.
mongos --port 27300 --fork --logpath
/opt/data/mongos/mongos_27300.log
--configdb
replcfg01/127.0.0.1:27201,127.0.0.1:27202,127.0.0.1:27203
Now, we an connect on our mongos server
using mongosh shell command.
3.5.
Adding Shards to Mongos
Shards are used to store data. They
provide high availability and data consistency. In production environment, each
shard is a separate replica set as follow:
To add shards in mongos, we use sh.addShard() method using the admin database.
[direct: mongos]
test> use admin
switched to db admin
[direct: mongos]
admin>
sh.addShard( "repl01/127.0.0.1:27101,127.0.0.1:27102,127.0.0.1:27103,127.0.0.1:27104,127.0.0.1:27100");
To see the status of the sharding status, we run the command sh.status() under the mongos prompt:
[direct: mongos]
admin> sh.status()
shardingVersion
{
_id: 1,
minCompatibleVersion: 5,
currentVersion: 6,
clusterId:
ObjectId("6153e945fbd96b9e59d869dd")
}
---
shards
[
{
_id: 'repl01',
host:
'repl01/127.0.0.1:27101,127.0.0.1:27102,127.0.0.1:27103,127.0.0.1:27104',
state: 1,
topologyTime: Timestamp({ t: 1632895183, i:
1 })
}
]
---
active mongoses
[ { '5.0.2': 1 } ]
---
autosplit
{ 'Currently enabled':
'yes' }
---
balancer
{
'Currently running': 'no',
'Currently enabled': 'yes',
'Failed balancer rounds in last 5 attempts':
0,
'Migration Results for the last 24 hours':
'No recent migrations'
}
---
databases
[
{
database: {
_id: 'compta',
primary: 'repl01',
partitioned: false,
version: {
uuid:
UUID("9bc29788-fc55-4b6f-8a10-1794a90febd1"),
timestamp: Timestamp({ t: 1632895183,
i: 2 }),
lastMod: 1
}
},
collections: {}
},
{
database: { _id: 'config', primary:
'config', partitioned: true },
collections: {
'config.system.sessions': {
shardKey: { _id: 1 },
unique: false,
balancing: true,
chunkMetadata: [ { shard: 'repl01',
nChunks: 1024 } ],
chunks: [
'too many chunks to print, use
verbose if you want to force print'
],
tags: []
}
}
}
]
[direct: mongos]
admin>
3.6.
Adding additional replica set nodes to sharding
Let’s add another 3 nodes replica set repl02 on our sharding cluster.
[root@linuxsvr01 ~]# mongod --replSet
repl02 --journal --port 27401 --shardsvr --dbpath /opt/data/repl02/inst01
--logpath /opt/data/repl02/inst01/mongod_27401.log –fork
about to fork child
process, waiting until server is ready for connections.
forked process: 57918
child process started
successfully, parent exiting
[root@linuxsvr01 ~]#
[root@linuxsvr01 ~]# mongod --replSet
repl02 --journal --port 27402 --shardsvr --dbpath /opt/data/repl02/inst02
--logpath /opt/data/repl02/inst01/mongod_27402.log –fork
about to fork child
process, waiting until server is ready for connections.
forked process: 57984
child process started
successfully, parent exiting
[root@linuxsvr01 ~]#
[root@linuxsvr01 ~]# mongod --replSet
repl02 --journal --port 27403 --shardsvr --dbpath /opt/data/repl02/inst03 --logpath
/opt/data/repl02/inst01/mongod_27403.log –fork
about to fork child
process, waiting until server is ready for connections.
forked process: 58045
child process started
successfully, parent exiting
[root@linuxsvr01 ~]#
[root@linuxsvr01 ~]# mongosh --port 27401
Current Mongosh Log ID: 61541eeee1fbd30b59fba380
Connecting to:
mongodb://127.0.0.1:27401/?directConnection=true&serverSelectionTimeoutMS=2000
Using MongoDB:
5.0.2
Using Mongosh:
1.0.5
For mongosh info see:
https://docs.mongodb.com/mongodb-shell/
------
The server
generated these startup warnings when booting:
2021-09-29T03:55:13.573-04:00: Using the XFS filesystem is strongly
recommended with the WiredTiger storage engine. See http://dochub.mongodb.org/core/prodnotes-filesystem
2021-09-29T03:55:14.537-04:00: Access control is not enabled for the
database. Read and write access to data and configuration is unrestricted
2021-09-29T03:55:14.537-04:00: You are running this process as the root
user, which is not recommended
2021-09-29T03:55:14.537-04:00: This server is bound to localhost. Remote
systems will be unable to connect to this server. Start the server with
--bind_ip <address> to specify which IP addresses it should serve
responses from, or with --bind_ip_all to bind to all interfaces. If this
behavior is desired, start the server with --bind_ip 127.0.0.1 to disable this
warning
2021-09-29T03:55:14.537-04:00:
/sys/kernel/mm/transparent_hugepage/enabled is 'always'. We suggest setting it
to 'never'
2021-09-29T03:55:14.537-04:00: Soft rlimits for open file descriptors
too low
------
Warning: Found ~/.mongorc.js, but not ~/.mongoshrc.js.
~/.mongorc.js will not be loaded.
You may want
to copy or rename ~/.mongorc.js to ~/.mongoshrc.js.
test>
test> rs.initiate( {
... _id :
"repl02",
... members:
[ {_id : 0, host : "127.0.0.1:27401"},
...
{_id : 1, host : "127.0.0.1:27402"},
...
{_id : 2, host : "127.0.0.1:27403"}
... ]
... })
{ ok: 1 }
repl02 [direct: other] test>
repl02 [direct: primary] test>
[root@linuxsvr01 ~]# mongosh
--port 27300
Current Mongosh Log
ID: 615420cf8b53c829ff63f6d5
Connecting to: mongodb://127.0.0.1:27300/?directConnection=true&serverSelectionTimeoutMS=2000
Using MongoDB: 5.0.2
Using Mongosh: 1.0.5
For mongosh info see:
https://docs.mongodb.com/mongodb-shell/
------
The server generated these startup warnings
when booting:
2021-09-29T00:30:11.523-04:00: Access
control is not enabled for the database. Read and write access to data and
configuration is unrestricted
2021-09-29T00:30:11.523-04:00: You are
running this process as the root user, which is not recommended
2021-09-29T00:30:11.523-04:00: This server
is bound to localhost. Remote systems will be unable to connect to this server.
Start the server with --bind_ip <address> to specify which IP addresses
it should serve responses from, or with --bind_ip_all to bind to all
interfaces. If this behavior is desired, start the server with --bind_ip
127.0.0.1 to disable this warning
------
Warning: Found
~/.mongorc.js, but not ~/.mongoshrc.js. ~/.mongorc.js will not be loaded.
You may want to copy or rename ~/.mongorc.js
to ~/.mongoshrc.js.
[direct: mongos]
test>
[direct: mongos] test> use admin
switched to db admin
[direct: mongos] admin>
[direct: mongos] admin> sh.addShard( "repl02/127.0.0.1:27401,127.0.0.1:27402,127.0.0.1:27403"
)
{
shardAdded: 'repl02',
ok: 1,
'$clusterTime': {
clusterTime: Timestamp({ t:
1632903493, i: 1 }),
signature: {
hash: Binary(Buffer.from("0000000000000000000000000000000000000000",
"hex"), 0),
keyId: Long("0")
}
},
operationTime: Timestamp({ t:
1632903492, i: 4 })
}
[direct: mongos] admin>
3.7. Shard a collection
Now we are going for testing our
sharding configuration. We are using test database as follow:
[direct: mongos] test>
[direct: mongos] test> var bulk =
db.big_collection.initializeUnorderedBulkOp();
[direct:
mongos] test> people = ["Mbadi", "Tonye",
"Moussa", "Onana", "Engolo", "Bello",
"Evembe", "Diabongue", "Essomba",
"Biya", "Mengolo", "Um Nyobe"];
[
'Mbadi',
'Tonye',
'Moussa',
'Onana',
'Engolo',
'Bello',
'Evembe',
'Diabongue',
'Essomba', 'Biya',
'Mengolo', 'Um Nyobe'
]
[direct: mongos] test> for(var i=0; i<2000000; i++){user_id =
i;name = people[Math.floor(Math.random()*people.length)];number =
Math.floor(Math.random()*10001);bulk.insert( { "user_id":user_id,
"name":name, "number":number });}
{ nInsertOps: 2000000, nUpdateOps: 0, nRemoveOps: 0, nBatches: 2003 }
[direct: mongos] test>
[direct:
mongos] test> bulk.execute();
{
acknowledged: true,
insertedCount: 2000000,
insertedIds: [
{ index: 0, _id:
ObjectId("615d7e62e3abab4e4107b2ea") },
{ index: 1, _id:
ObjectId("615d7e62e3abab4e4107b2eb") },
{ index: 2, _id: ObjectId("615d7e62e3abab4e4107b2ec")
},
{ index: 3, _id:
ObjectId("615d7e62e3abab4e4107b2ed") },
{ index: 4, _id:
ObjectId("615d7e62e3abab4e4107b2ee") },
{ index: 5, _id:
ObjectId("615d7e62e3abab4e4107b2ef") },
{ index: 6, _id:
ObjectId("615d7e62e3abab4e4107b2f0") },
{ index: 7, _id:
ObjectId("615d7e62e3abab4e4107b2f1") },
{ index: 8, _id:
ObjectId("615d7e62e3abab4e4107b2f2") },
{ index: 9, _id:
ObjectId("615d7e62e3abab4e4107b2f3") },
{ index: 10, _id:
ObjectId("615d7e62e3abab4e4107b2f4") },
{ index: 11, _id:
ObjectId("615d7e62e3abab4e4107b2f5") },
{ index: 12, _id:
ObjectId("615d7e62e3abab4e4107b2f6") },
{ index: 13, _id:
ObjectId("615d7e62e3abab4e4107b2f7") },
{ index: 14, _id:
ObjectId("615d7e62e3abab4e4107b2f8") },
{ index: 15, _id:
ObjectId("615d7e62e3abab4e4107b2f9") },
{ index: 16, _id:
ObjectId("615d7e62e3abab4e4107b2fa") },
{ index: 17, _id: ObjectId("615d7e62e3abab4e4107b2fb")
},
{ index: 18, _id:
ObjectId("615d7e62e3abab4e4107b2fc") },
{ index: 19, _id:
ObjectId("615d7e62e3abab4e4107b2fd") },
{ index: 20, _id:
ObjectId("615d7e62e3abab4e4107b2fe") },
{ index: 21, _id: ObjectId("615d7e62e3abab4e4107b2ff")
},
{ index: 22, _id:
ObjectId("615d7e62e3abab4e4107b300") },
{ index: 23, _id:
ObjectId("615d7e62e3abab4e4107b301") },
{ index: 24, _id:
ObjectId("615d7e62e3abab4e4107b302") },
{ index: 25, _id:
ObjectId("615d7e62e3abab4e4107b303") },
{ index: 26, _id:
ObjectId("615d7e62e3abab4e4107b304") },
{ index: 27, _id:
ObjectId("615d7e62e3abab4e4107b305") },
{ index: 28, _id:
ObjectId("615d7e62e3abab4e4107b306") },
{ index: 29, _id:
ObjectId("615d7e62e3abab4e4107b307") },
{ index: 30, _id:
ObjectId("615d7e62e3abab4e4107b308") },
{ index: 31, _id:
ObjectId("615d7e62e3abab4e4107b309") },
{ index: 32, _id:
ObjectId("615d7e62e3abab4e4107b30a") },
{ index: 33, _id:
ObjectId("615d7e62e3abab4e4107b30b") },
{ index: 34, _id:
ObjectId("615d7e62e3abab4e4107b30c") },
{ index: 35, _id:
ObjectId("615d7e62e3abab4e4107b30d") },
{ index: 36, _id:
ObjectId("615d7e62e3abab4e4107b30e") },
{ index: 37, _id:
ObjectId("615d7e62e3abab4e4107b30f") },
{ index: 38, _id:
ObjectId("615d7e62e3abab4e4107b310") },
{ index: 39, _id:
ObjectId("615d7e62e3abab4e4107b311") },
{ index: 40, _id:
ObjectId("615d7e62e3abab4e4107b312") },
{ index: 41, _id:
ObjectId("615d7e62e3abab4e4107b313") },
{ index: 42, _id:
ObjectId("615d7e62e3abab4e4107b314") },
{ index: 43, _id:
ObjectId("615d7e62e3abab4e4107b315") },
{ index: 44, _id: ObjectId("615d7e62e3abab4e4107b316")
},
{ index: 45, _id:
ObjectId("615d7e62e3abab4e4107b317") },
{ index: 46, _id:
ObjectId("615d7e62e3abab4e4107b318") },
{ index: 47, _id:
ObjectId("615d7e62e3abab4e4107b319") },
{ index: 48, _id: ObjectId("615d7e62e3abab4e4107b31a")
},
{ index: 49, _id:
ObjectId("615d7e62e3abab4e4107b31b") },
{ index: 50, _id:
ObjectId("615d7e62e3abab4e4107b31c") },
{ index: 51, _id:
ObjectId("615d7e62e3abab4e4107b31d") },
{ index: 52, _id: ObjectId("615d7e62e3abab4e4107b31e")
},
{ index: 53, _id:
ObjectId("615d7e62e3abab4e4107b31f") },
{ index: 54, _id:
ObjectId("615d7e62e3abab4e4107b320") },
{ index: 55, _id:
ObjectId("615d7e62e3abab4e4107b321") },
{ index: 56, _id:
ObjectId("615d7e62e3abab4e4107b322") },
{ index: 57, _id:
ObjectId("615d7e62e3abab4e4107b323") },
{ index: 58, _id:
ObjectId("615d7e62e3abab4e4107b324") },
{ index: 59, _id:
ObjectId("615d7e62e3abab4e4107b325") },
{ index: 60, _id:
ObjectId("615d7e62e3abab4e4107b326") },
{ index: 61, _id:
ObjectId("615d7e62e3abab4e4107b327") },
{ index: 62, _id:
ObjectId("615d7e62e3abab4e4107b328") },
{ index: 63, _id:
ObjectId("615d7e62e3abab4e4107b329") },
{ index: 64, _id:
ObjectId("615d7e62e3abab4e4107b32a") },
{ index: 65, _id:
ObjectId("615d7e62e3abab4e4107b32b") },
{ index: 66, _id:
ObjectId("615d7e62e3abab4e4107b32c") },
{ index: 67, _id:
ObjectId("615d7e62e3abab4e4107b32d") },
{ index: 68, _id:
ObjectId("615d7e62e3abab4e4107b32e") },
{ index: 69, _id:
ObjectId("615d7e62e3abab4e4107b32f") },
{ index: 70, _id:
ObjectId("615d7e62e3abab4e4107b330") },
{ index: 71, _id:
ObjectId("615d7e62e3abab4e4107b331") },
{ index: 72, _id:
ObjectId("615d7e62e3abab4e4107b332") },
{ index: 73, _id:
ObjectId("615d7e62e3abab4e4107b333") },
{ index: 74, _id:
ObjectId("615d7e62e3abab4e4107b334") },
{ index: 75, _id:
ObjectId("615d7e62e3abab4e4107b335") },
{ index: 76, _id: ObjectId("615d7e62e3abab4e4107b336")
},
{ index: 77, _id:
ObjectId("615d7e62e3abab4e4107b337") },
{ index: 78, _id:
ObjectId("615d7e62e3abab4e4107b338") },
{ index: 79, _id:
ObjectId("615d7e62e3abab4e4107b339") },
{ index: 80, _id: ObjectId("615d7e62e3abab4e4107b33a")
},
{ index: 81, _id:
ObjectId("615d7e62e3abab4e4107b33b") },
{ index: 82, _id:
ObjectId("615d7e62e3abab4e4107b33c") },
{ index: 83, _id:
ObjectId("615d7e62e3abab4e4107b33d") },
{ index: 84, _id: ObjectId("615d7e62e3abab4e4107b33e")
},
{ index: 85, _id:
ObjectId("615d7e62e3abab4e4107b33f") },
{ index: 86, _id:
ObjectId("615d7e62e3abab4e4107b340") },
{ index: 87, _id:
ObjectId("615d7e62e3abab4e4107b341") },
{ index: 88, _id:
ObjectId("615d7e62e3abab4e4107b342") },
{ index: 89, _id:
ObjectId("615d7e62e3abab4e4107b343") },
{ index: 90, _id:
ObjectId("615d7e62e3abab4e4107b344") },
{ index: 91, _id:
ObjectId("615d7e62e3abab4e4107b345") },
{ index: 92, _id:
ObjectId("615d7e62e3abab4e4107b346") },
{ index: 93, _id:
ObjectId("615d7e62e3abab4e4107b347") },
{ index: 94, _id:
ObjectId("615d7e62e3abab4e4107b348") },
{ index: 95, _id:
ObjectId("615d7e62e3abab4e4107b349") },
{ index: 96, _id:
ObjectId("615d7e62e3abab4e4107b34a") },
{ index: 97, _id:
ObjectId("615d7e62e3abab4e4107b34b") },
{ index: 98, _id:
ObjectId("615d7e62e3abab4e4107b34c") },
{ index: 99, _id:
ObjectId("615d7e62e3abab4e4107b34d") },
... 1999900 more items
],
matchedCount: 0,
modifiedCount: 0,
deletedCount: 0,
upsertedCount: 0,
upsertedIds: []
}
[direct:
mongos] test>
[direct: mongos] test> sh.enableSharding( "test" )
{
ok: 1,
'$clusterTime': {
clusterTime: Timestamp({ t:
1633517943, i: 2 }),
signature: {
hash:
Binary(Buffer.from("0000000000000000000000000000000000000000",
"hex"), 0),
keyId: Long("0")
}
},
operationTime: Timestamp({ t:
1633517943, i: 2 })
}
[direct: mongos] test> db.big_collection.createIndex( { number : 1
} )
number_1
[direct: mongos] test>
[direct: mongos]
test>
sh.shardCollection("test.big_collection",{"number":1});
{
collectionsharded: 'test.big_collection',
ok: 1,
'$clusterTime': {
clusterTime: Timestamp({ t: 1633518159, i:
4 }),
signature: {
hash: Binary(Buffer.from("0000000000000000000000000000000000000000",
"hex"), 0),
keyId: Long("0")
}
},
operationTime: Timestamp({ t: 1633518158, i:
6 })
}
[direct:
mongos] test>
[direct:
mongos] test> db.printShardingStatus()
shardingVersion
{
_id: 1,
minCompatibleVersion: 5,
currentVersion: 6,
clusterId:
ObjectId("6153e945fbd96b9e59d869dd")
}
---
shards
[
{
_id: 'repl01',
host:
'repl01/127.0.0.1:27101,127.0.0.1:27102,127.0.0.1:27103,127.0.0.1:27104',
state: 1,
topologyTime: Timestamp({ t: 1632895183, i:
1 })
},
{
_id: 'repl02',
host:
'repl02/127.0.0.1:27401,127.0.0.1:27402,127.0.0.1:27403',
state: 1,
topologyTime: Timestamp({ t: 1632903492, i:
2 })
}
]
---
active
mongoses
[ {
'5.0.2': 1 } ]
---
autosplit
{
'Currently enabled': 'yes' }
---
balancer
{
'Currently running': 'no',
'Failed balancer rounds in last 5 attempts':
4,
'Last reported error': 'Could not find host
matching read preference { mode: "primary" } for set repl02',
'Time of Reported error':
ISODate("2021-10-06T09:20:01.132Z"),
'Currently enabled': 'yes',
'Migration Results for the last 24 hours':
'No recent migrations'
}
---
databases
[
{
database: {
_id: 'compta',
primary: 'repl01',
partitioned: false,
version: {
uuid:
UUID("9bc29788-fc55-4b6f-8a10-1794a90febd1"),
timestamp: Timestamp({ t: 1632895183,
i: 2 }),
lastMod: 1
}
},
collections: {}
},
{
database: { _id: 'config', primary:
'config', partitioned: true },
collections: {
'config.system.sessions': {
shardKey: { _id: 1 },
unique: false,
balancing: true,
chunkMetadata: [
{ shard: 'repl01', nChunks: 512 },
{ shard: 'repl02', nChunks: 512 }
],
chunks: [
'too many chunks to print, use
verbose if you want to force print'
],
tags: []
}
}
},
{
database: {
_id: 'people',
primary: 'repl02',
partitioned: true,
version: {
uuid:
UUID("0fb50b4f-1556-4b7f-8d22-db4f90748f4a"),
timestamp: Timestamp({ t: 1632908273,
i: 2 }),
lastMod: 1
}
},
collections: {}
},
{
database: {
_id: 'test',
primary: 'repl01',
partitioned: true,
version: {
uuid:
UUID("720d5514-53f3-473c-a807-0326bc2335c5"),
timestamp: Timestamp({ t: 1633438992,
i: 1 }),
lastMod: 1
}
},
collections: {
'test.big_collection': {
shardKey: { number: 1 },
unique: false,
balancing: true,
chunkMetadata: [ { shard: 'repl01',
nChunks: 4 } ],
chunks: [
{ min: { number: MinKey() }, max: {
number: 2622 }, 'on shard': 'repl01', 'last modified': Timestamp({ t: 1, i: 0
}) },
{ min: { number: 2622 }, max: {
number: 5246 }, 'on shard': 'repl01', 'last modified': Timestamp({ t: 1, i: 1
}) },
{ min: { number: 5246 }, max: {
number: 7869 }, 'on shard': 'repl01', 'last modified': Timestamp({ t: 1, i: 2
}) },
{ min: { number: 7869 }, max: {
number: MaxKey() }, 'on shard': 'repl01', 'last modified': Timestamp({ t: 1, i:
3 }) }
],
tags: []
}
}
}
]
[direct:
mongos] test>
[direct:
mongos] test> db.big_collection.getShardDistribution();
Shard
repl01 at
repl01/127.0.0.1:27101,127.0.0.1:27102,127.0.0.1:27103,127.0.0.1:27104
{
data: '122.22MiB',
docs: 2000000,
chunks: 3,
'estimated data per chunk': '40.74MiB',
'estimated docs per chunk': 666666
}
---
Shard
repl02 at repl02/127.0.0.1:27401,127.0.0.1:27402,127.0.0.1:27403
{
data: '32.04MiB',
docs: 524268,
chunks: 1,
'estimated data per chunk': '32.04MiB',
'estimated docs per chunk': 524268
}
---
Totals
{
data: '154.26MiB',
docs: 2524268,
chunks: 4,
'Shard repl01': [
'79.23 % data',
'79.23 % docs in cluster',
'64B avg obj size on shard'
],
'Shard repl02': [
'20.76 % data',
'20.76 % docs in cluster',
'64B avg obj size on shard'
]
}
[direct:
mongos] test>
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