Create a local mongo replica set for dev or testing

Usage no npm install needed!

<script type="module">
  import 42nthMrepset from 'https://cdn.skypack.dev/@42nth/mrepset';


MongoDB Replica Set


This script is meant to be used only for dev & testing environment as it comes with no security setup.

It should only be used for localhost or on any secured environment, not into the global internet.


This script will configure a MongoDB replica set environment and start all the replica set mongod processes.

By default it will create a replica set rs of 3 nodes on localhost with a db path of /srv/mongo:

  • node #1, rs-0 on port 27017,
  • node #2, rs-1 on port 27018,
  • node #3, rs-2 on port 27019.

Each process will have its own log files streamed to disk :

  • access log : <dbPath>/log/rs-X/access.log,
  • error log : <dbPath>/log/rs-X/error.log.

Closing the main process will terminate the three processes.


Locally :

  • npm : npm i @42nth/mrepset
  • yarn : yarn add @42nth/mrepset

Or globally :

  • npm : npm i -g @42nth/mrepset
  • yarn : yarn global add @42nth/mrepset


const setup = require('mrepset')



Replica Set options

name (default: 'rs')

The name of the replica set.

baseDir (default '/srv/mongodb')

The base directory of the MongoDB instance. Must be writable by the current user or the process will failed.

port (default 27017)

Default MongoDB port. You can override it to any value N you want and it will use the value N, N+1 and N+2 for the 3 nodes.

oplog (default 128)

Use a slow value by default as it should only be used for testing purposes. Not the values you would use in production.

nodes (default 3)

The number of nodes to create in the replicat set.

ip (default '')

The ip the server will listen to.

Generic options


The path to find the MongoDB binaries. Useful if you have multiple MongoDB versions to point a specific MongoDB version bin path.

accessLog (default 'access.log')

The name of a node access log file.

errorLog (default 'error.log')

The name of a node error log file.



In the example below a replica set of 3 nodes starting on port 27117, 27118 & 27119 using a MongoDB@4.0 installation in /usr/local/opt/mongodb@4.0 folder :

const setup = require('@42nth/mrepset')

  rs: {
    port: 27117,
    baseDir: '/opt/mongodb'
  mongo: {
    mongodPath: '/usr/local/opt/mongodb@4.0/bin',

You can see a local version in the examples/setup.js file.


This module export the mrepset CLI.

$ mrepset --baseDir /opt/mongodb

Access all options :

$ mrepset --help

If you want to access debug logs add the DEBUG flag on the CLI with the mongo:rs flag.

You can see a local version in the examples/setup.sh file which can be run :

$ ./examples/setup.sh