EphemeralMongo - temporary and disposable MongoDB for integration tests and local debugging

• Introduction
• Usage
• How it works
• Reducing the download size
• Windows Defender Firewall prompt
• Optimization tips
• Changelog

Introduction

EphemeralMongo is a set of multiple NuGet packages wrapping the binaries of MongoDB 6, 7, and 8. Each package targets .NET Standard 2.0, which means you can use it with .NET Framework 4.5.2 up to .NET 9 and later.

The supported operating systems are Linux (x64), macOS (arm64), and Windows (x64). Each package provides access to:

• Multiple ephemeral and isolated MongoDB databases for running tests,
• A quick way to set up a MongoDB database for a local development environment,
• mongoexport and mongoimport tools for exporting and importing collections,
• Support for single-node replica sets, enabling transactions and change streams.

This project follows in the footsteps of Mongo2Go and expands upon its foundation.

Package	Description	Link
EphemeralMongo6	All-in-one package for MongoDB 6.0.21 on Linux, macOS, and Windows
EphemeralMongo7	All-in-one package for MongoDB 7.0.18 on Linux, macOS, and Windows
EphemeralMongo8	All-in-one package for MongoDB 8.0.6 on Linux, macOS, and Windows

Usage

Use the static MongoRunner.Run() method to create a disposable instance that provides access to a MongoDB connection string, import, and export tools:

// All properties below are optional. The whole "options" instance is optional too!
var options = new MongoRunnerOptions
{
    UseSingleNodeReplicaSet = true, // Default: false
    StandardOutputLogger = line => Console.WriteLine(line), // Default: null
    StandardErrorLogger = line => Console.WriteLine(line), // Default: null
    DataDirectory = "/path/to/data/", // Default: null
    BinaryDirectory = "/path/to/mongo/bin/", // Default: null
    ConnectionTimeout = TimeSpan.FromSeconds(10), // Default: 30 seconds
    ReplicaSetSetupTimeout = TimeSpan.FromSeconds(5), // Default: 10 seconds
    AdditionalArguments = "--quiet", // Default: null
    MongoPort = 27017, // Default: random available port
    DataDirectoryLifetime = TimeSpan.FromDays(1), // Default: 12 hours
};

// Disposing the runner will kill the MongoDB process (mongod) and delete the associated data directory
using (var runner = MongoRunner.Run(options))
{
    var database = new MongoClient(runner.ConnectionString).GetDatabase("default");

    // Do something with the database
    database.CreateCollection("people");

    // Export a collection. Full method signature:
    // Export(string database, string collection, string outputFilePath, string? additionalArguments = null)
    runner.Export("default", "people", "/path/to/default.json");

    // Import a collection. Full method signature:
    // Import(string database, string collection, string inputFilePath, string? additionalArguments = null, bool drop = false)
    runner.Import("default", "people", "/path/to/default.json");
}

How it works

• At build time, the MongoDB binaries (mongod, mongoimport, and mongoexport) are copied to your project output directory,
• At runtime, the library chooses the right binaries for your operating system,
• MongoRunner.Run always starts a new mongod process with a random available port,
• The resulting connection string will depend on your options (UseSingleNodeReplicaSet and AdditionalArguments),
• By default, a unique temporary data directory is used.

Reducing the download size

EphemeralMongo6, 7, and 8 are NuGet metapackages that reference dedicated runtime packages for Linux, macOS, and Windows. As of now, there isn't a way to optimize NuGet package downloads for a specific operating system (see #2). However, one can still avoid referencing the metapackage and directly reference the dependencies instead. Add MSBuild OS platform conditions and you'll get optimized NuGet imports for your OS and fewer downloads.

Instead of doing this:

<PackageReference Include="EphemeralMongo8" Version="*" />

Do this:

<PackageReference Include="EphemeralMongo.Core" Version="*" />
<PackageReference Include="EphemeralMongo8.runtime.linux-x64" Version="*" Condition="$([MSBuild]::IsOSPlatform('Linux'))" />
<PackageReference Include="EphemeralMongo8.runtime.osx-arm64" Version="*" Condition="$([MSBuild]::IsOSPlatform('OSX'))" />
<PackageReference Include="EphemeralMongo8.runtime.win-x64" Version="*" Condition="$([MSBuild]::IsOSPlatform('Windows'))" />

Windows Defender Firewall prompt

On Windows, you might get a Windows Defender Firewall prompt. This is because EphemeralMongo starts the mongod.exe process from your build output directory, and mongod.exe tries to open an available port (see here).

Optimization tips

Avoid calling MongoRunner.Run concurrently, as this will create many mongod processes and make your operating system slower. Instead, try to use a single instance and reuse it - create as many databases as you need, one per test, for example.

Check out this gist for an implementation of a reusable IMongoRunner.

Changelog

2.0.0

• Breaking change: Support for MongoDB 5.0 and 6.0 has been removed, as their end-of-life has passed.
• Breaking change: arm64 is now the default target for macOS. The previous target was x64.
• Breaking change: The Linux runtime package now uses Ubuntu 22.04's MongoDB binaries instead of the 18.04 ones. OpenSSL 3.0 is now required.
• Breaking change: Updated the MongoDB C# driver to 2.28.0, which now uses strong-named assemblies.
• Added support for MongoDB 8.0.
• Introduced data directory management to delete old data directories automatically.
• Use direct connection in replica set connection strings.
• Fixed the spelling issue in MongoRunnerOptions.StandardOutputLogger.