![]() ![]() A replica set can have up to 50 members, but a maximum of 7 can vote in an election. In the event that the primary member becomes unavailable, an automated election process happens among the secondary nodes to choose a new primary. One feature that distinguishes MongoDB’s replica sets from other replication implementations is their automatic failover mechanism. Thus, such a configuration isn’t ideal for every use case. You can configure your setup to read from one or more of the secondary members, but since data is transferred asynchronously, reads from secondary nodes can result in old data being served. Multiple primaries accepting write operations would lead to data conflicts.īy default, applications will only query the primary member for both read and write operations. Each replica set can have only one primary member at a time, as replication happens by copying the primary’s oplog (short for “operations log”) and repeating the logged changes on the secondaries’ respective data sets. The primary member is the main access point for transactions with the replica set and is the only member that can accept write operations. Every replica set must have one primary member and at least one secondary member. Each running instance of MongoDB that’s part of a given replica set is referred to as one of its members. Lastly, commands that must be run or file changes that must be made on every server will have a standard black background, like this:Īs mentioned in the introduction, MongoDB handles replication through an implementation called replica sets. Any examples showing commands or file changes performed on mongo0 will have a blue background, like this:Ĭommands and file changes performed on mongo1 will have a pink background:Įxample actions on mongo2 will have a green background: Please note that, for clarity, this guide will refer to the three servers as mongo0, mongo1, and mongo2. ![]() To this end, follow our tutorial on How To Install MongoDB on Ubuntu 20.04, making sure to complete each step on all three of your servers. MongoDB installed on each of your Ubuntu servers.To set this up, follow our initial server setup guide for Ubuntu 20.04. All three of these servers should have a non-root administrative user and a firewall configured with UFW. Three servers, each running Ubuntu 20.04.If you plan on using your replica set for testing or development, we strongly encourage you to follow our tutorial on How To Configure Keyfile Authentication for MongoDB Replica Sets on Ubuntu 20.04. For production deployments that employ replication, the MongoDB documentation recommends using x.509 authentication, and it describes keyfiles as “bare-minimum forms of security” that are “best suited for testing or development environments.” However, the process of obtaining and configuring x.509 certificates comes with a number of caveats and decisions that must be made on a case-by-case basis, which is beyond the scope of a DigitalOcean tutorial. The Community version of MongoDB comes with two authentication methods that can help keep your database secure, keyfile authentication and x.509 authentication. This setup is not recommended for production environments. Upon completing this tutorial you’ll have a functioning replica set, but it will not have any security features enabled. Note: Be aware that the procedure outlined in this guide is intended to demonstrate how to get a replica set up and running quickly. In this example configuration, each member of the replica set will be a distinct MongoDB instance running on separate Ubuntu 20.04 servers. This tutorial provides a brief overview of how replication works in MongoDB and outlines how to configure and initiate a replica set with three members. In MongoDB, a group of servers that maintain the same data set through replication are referred to as a replica set. The practice of synchronizing data across multiple separate databases is called replication. ![]() This provides redundancy in case one of the database servers fails and can improve a database’s availability and scalability, as well as reduce read latencies. When working with databases, it’s often useful to have multiple copies of your data. This means that, unlike relational databases, MongoDB does not require a predefined schema before you add data to a database. ![]() Instead, it uses JSON-like documents with dynamic schemas. It is classified as a NoSQL database because it does not rely on a traditional table-based relational database structure. MongoDB is a document-oriented database used in many modern web applications. An earlier version of this tutorial was written by Justin Ellingwood. ![]()
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