Deploy a Replica Set for Testing and Development
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This procedure describes deploying a replica set in a development or test environment. For a production deployment, refer to the Deploy a Replica Set tutorial.
This tutorial describes how to create a three-member replica set from three existing mongod
instances running with
access control disabled.
To deploy a replica set with enabled access control, see Deploy Replica Set With Keyfile Authentication. If you wish to deploy a replica set from a single MongoDB instance, see Convert a Standalone to a Replica Set. For more information on replica set deployments, see the Replication and Replica Set Deployment Architectures documentation.
Overview
Three member replica sets provide enough redundancy to survive most network partitions and other system failures. These sets also have sufficient capacity for many distributed read operations. Replica sets should always have an odd number of members. This ensures that elections will proceed smoothly. For more about designing replica sets, see the Replication overview.
Requirements
For test and development systems, you can run your mongod
instances on a local system, or within a virtual instance.
Before you can deploy a replica set, you must install MongoDB on each system that will be part of your replica set. If you have not already installed MongoDB, see the installation tutorials.
Each member must be able to connect to every other member. For instructions on how to check your connection, see Test Connections Between all Members.
Considerations
Tip
When possible, use a logical DNS hostname instead of an ip address, particularly when configuring replica set members or sharded cluster members. The use of logical DNS hostnames avoids configuration changes due to ip address changes.
IP Binding
Starting in MongoDB 3.6, MongoDB binaries, mongod
and
mongos
, bind to localhost by default. If the
net.ipv6
configuration file setting or the --ipv6
command line option is set for the binary, the binary additionally binds
to the localhost IPv6 address.
Previously, starting from MongoDB 2.6, only the binaries from the official MongoDB RPM (Red Hat, CentOS, Fedora Linux, and derivatives) and DEB (Debian, Ubuntu, and derivatives) packages bind to localhost by default.
When bound only to the localhost, these MongoDB 3.6 binaries can only
accept connections from clients (including the mongo
shell,
other members in your deployment for replica sets and sharded clusters)
that are running on the same machine. Remote clients cannot connect to
the binaries bound only to localhost.
To override and bind to other ip addresses, you can use the
net.bindIp
configuration file setting or the
--bind_ip
command-line option to specify a list of hostnames or ip
addresses.
Warning
Before binding to a non-localhost (e.g. publicly accessible) IP address, ensure you have secured your cluster from unauthorized access. For a complete list of security recommendations, see Security Checklist. At minimum, consider enabling authentication and hardening network infrastructure.
For example, the following mongod
instance binds to both
the localhost and the hostname My-Example-Associated-Hostname
, which is
associated with the ip address 198.51.100.1
:
mongod --bind_ip localhost,My-Example-Associated-Hostname
In order to connect to this instance, remote clients must specify
the hostname or its associated ip address 198.51.100.1
:
mongo --host My-Example-Associated-Hostname mongo --host 198.51.100.1
In this test deployment, the three members run on the same machine.
Replica Set Naming
Important
These instructions should only be used for test or development deployments.
The examples in this procedure create a new replica set named rs0
.
If your application connects to more than one replica set, each set must have a distinct name. Some drivers group replica set connections by replica set name.
Procedure
Tip
When possible, use a logical DNS hostname instead of an ip address, particularly when configuring replica set members or sharded cluster members. The use of logical DNS hostnames avoids configuration changes due to ip address changes.
Create the necessary data directories for each member by issuing a command similar to the following:
mkdir -p /srv/mongodb/rs0-0 /srv/mongodb/rs0-1 /srv/mongodb/rs0-2 This will create directories called "rs0-0", "rs0-1", and "rs0-2", which will contain the instances' database files.
Start your
mongod
instances in their own shell windows by issuing the following commands:Warning
Before binding to a non-localhost (e.g. publicly accessible) IP address, ensure you have secured your cluster from unauthorized access. For a complete list of security recommendations, see Security Checklist. At minimum, consider enabling authentication and hardening network infrastructure.
First member:
mongod --replSet rs0 --port 27017 --bind_ip localhost,<hostname(s)|ip address(es)> --dbpath /srv/mongodb/rs0-0 --oplogSize 128 Second member:
mongod --replSet rs0 --port 27018 --bind_ip localhost,<hostname(s)|ip address(es)> --dbpath /srv/mongodb/rs0-1 --oplogSize 128 Third member:
mongod --replSet rs0 --port 27019 --bind_ip localhost,<hostname(s)|ip address(es)> --dbpath /srv/mongodb/rs0-2 --oplogSize 128 This starts each instance as a member of a replica set named
rs0
, each running on a distinct port, and specifies the path to your data directory with the--dbpath
setting. If you are already using the suggested ports, select different ports.The instances bind to both the localhost and the ip address of the host.
The
--oplogSize
setting reduces the disk space that eachmongod
instance uses. [1] This is ideal for testing and development deployments as it prevents overloading your machine. For more information on this and other configuration options, see Configuration File Options.Connect to one of your
mongod
instances through themongo
shell. You will need to indicate which instance by specifying its port number. For the sake of simplicity and clarity, you may want to choose the first one, as in the following command;mongo --port 27017 In the
mongo
shell, users.initiate()
to initiate the replica set. You can create a replica set configuration object in themongo
shell environment, as in the following example:rsconf = { _id: "rs0", members: [ { _id: 0, host: "<hostname>:27017" }, { _id: 1, host: "<hostname>:27018" }, { _id: 2, host: "<hostname>:27019" } ] } replacing
<hostname>
with your system's hostname, and then pass thersconf
file tors.initiate()
as follows:rs.initiate( rsconf ) Display the current replica configuration by issuing the following command:
rs.conf() The replica set configuration object resembles the following:
{ "_id" : "rs0", "version" : 1, "protocolVersion" : NumberLong(1), "members" : [ { "_id" : 0, "host" : "<hostname>:27017", "arbiterOnly" : false, "buildIndexes" : true, "hidden" : false, "priority" : 1, "tags" : { }, "slaveDelay" : NumberLong(0), "votes" : 1 }, { "_id" : 1, "host" : "<hostname>:27018", "arbiterOnly" : false, "buildIndexes" : true, "hidden" : false, "priority" : 1, "tags" : { }, "slaveDelay" : NumberLong(0), "votes" : 1 }, { "_id" : 2, "host" : "<hostname>:27019", "arbiterOnly" : false, "buildIndexes" : true, "hidden" : false, "priority" : 1, "tags" : { }, "slaveDelay" : NumberLong(0), "votes" : 1 } ], "settings" : { "chainingAllowed" : true, "heartbeatIntervalMillis" : 2000, "heartbeatTimeoutSecs" : 10, "electionTimeoutMillis" : 10000, "catchUpTimeoutMillis" : -1, "getLastErrorModes" : { }, "getLastErrorDefaults" : { "w" : 1, "wtimeout" : 0 }, "replicaSetId" : ObjectId("598f630adc9053c6ee6d5f38") } }
Check the status of your replica set at any time with the
rs.status()
operation.
Tip
See also:
The documentation of the following shell functions for more information:
You may also consider the simple setup script as an example of a basic automatically-configured replica set.
Refer to Replica Set Read and Write Semantics for a detailed explanation of read and write semantics in MongoDB.
[1] | The oplog can grow past its configured size
limit to avoid deleting the majority commit point . |