feat: Add MongoDB replica set support

docs/modules/mongodb.md

@@ -45,3 +45,12 @@ public sealed class MongoDbContainerTest : IAsyncLifetime
 ```
 
 To execute the tests, use the command `dotnet test` from a terminal.
+
+## MongoDb Replica Set
+
+By default, MongoDB runs as a standalone instance. If your tests require a MongoDB replica set, use the code below which will initialise it as a single node replica set:
+
+```csharp
+    private readonly MongoDbContainer _mongoDbContainer =
+        new MongoDbBuilder().WithReplicaSet().Build();
+```

src/Testcontainers.MongoDb/MongoDbBuilder.cs

@@ -60,6 +60,13 @@ public MongoDbBuilder WithPassword(string password)
             .WithEnvironment("MONGO_INITDB_ROOT_PASSWORD", initDbRootPassword);
     }
 
+    public MongoDbBuilder WithReplicaSet(string replicaSetName = "rs0")
+    {
+        var initReplicaSetName = replicaSetName ?? "rs0";
+
+        return Merge(DockerResourceConfiguration, new MongoDbConfiguration(replicaSetName: initReplicaSetName));
+    }
+
     /// <inheritdoc />
     public override MongoDbContainer Build()
     {
@@ -69,6 +76,22 @@ public override MongoDbContainer Build()
         // provided, the log message "Waiting for connections" appears twice.
         // If the user does not provide a custom waiting strategy, append the default MongoDb waiting strategy.
         var mongoDbBuilder = DockerResourceConfiguration.WaitStrategies.Count() > 1 ? this : WithWaitStrategy(Wait.ForUnixContainer().AddCustomWaitStrategy(new WaitUntil(DockerResourceConfiguration)));
+
+        if (!string.IsNullOrEmpty(DockerResourceConfiguration.ReplicaSetName))
+        {
+            mongoDbBuilder = mongoDbBuilder
+                .WithCommand(DockerResourceConfiguration.Command.Concat(["--replSet", DockerResourceConfiguration.ReplicaSetName, "--keyFile", "/tmp/keyfile", "--bind_ip_all"]).ToArray())
+                .WithResourceMapping(Encoding.Default.GetBytes("""
+                    #!/bin/bash
+                    openssl rand -base64 32 > "/tmp/keyfile"
+                    chmod 600 /tmp/keyfile
+                    chown 999:999 /tmp/keyfile
+                    """.Replace("\r", "")), "/docker-entrypoint-initdb.d/01-init-keyfile.sh", UnixFileModes.OtherRead | UnixFileModes.OtherExecute)
+                .WithWaitStrategy(Wait.ForUnixContainer().UntilCommandIsCompleted(
+                    "mongosh -u $MONGO_INITDB_ROOT_USERNAME -p $MONGO_INITDB_ROOT_PASSWORD --quiet --eval " +
+                    $"\"try {{ rs.status().ok }} catch (e) {{ rs.initiate({{'_id':'{DockerResourceConfiguration.ReplicaSetName}', members: [{{'_id':1, 'host':'127.0.0.1:27017'}}]}}).ok }}\""));
+        }
+
         return new MongoDbContainer(mongoDbBuilder.DockerResourceConfiguration);
     }
 

src/Testcontainers.MongoDb/MongoDbConfiguration.cs

@@ -11,10 +11,12 @@ public sealed class MongoDbConfiguration : ContainerConfiguration
     /// <param name="password">The MongoDb password.</param>
     public MongoDbConfiguration(
         string username = null,
-        string password = null)
+        string password = null,
+        string replicaSetName = null)
     {
         Username = username;
         Password = password;
+        ReplicaSetName = replicaSetName;
     }
 
     /// <summary>
@@ -57,6 +59,7 @@ public MongoDbConfiguration(MongoDbConfiguration oldValue, MongoDbConfiguration
     {
         Username = BuildConfiguration.Combine(oldValue.Username, newValue.Username);
         Password = BuildConfiguration.Combine(oldValue.Password, newValue.Password);
+        ReplicaSetName = BuildConfiguration.Combine(oldValue.ReplicaSetName, newValue.ReplicaSetName);
     }
 
     /// <summary>
@@ -68,4 +71,10 @@ public MongoDbConfiguration(MongoDbConfiguration oldValue, MongoDbConfiguration
     /// Gets the MongoDb password.
     /// </summary>
     public string Password { get; }
+
+    /// <summary>
+    /// Name of the replica set. If specified, the container will be started as a single node replica set.
+    /// </summary>
+    /// <example>rs0</example>
+    public string ReplicaSetName { get; }
 }

tests/Testcontainers.MongoDb.Tests/MongoDbContainerTest.cs

@@ -3,10 +3,12 @@ namespace Testcontainers.MongoDb;
 public abstract class MongoDbContainerTest : IAsyncLifetime
 {
     private readonly MongoDbContainer _mongoDbContainer;
+    private readonly bool _isReplicaSet;
 
-    private MongoDbContainerTest(MongoDbContainer mongoDbContainer)
+    private MongoDbContainerTest(MongoDbContainer mongoDbContainer, bool isReplicaSet = false)
     {
         _mongoDbContainer = mongoDbContainer;
+        _isReplicaSet = isReplicaSet;
     }
 
     public Task InitializeAsync()
@@ -49,6 +51,31 @@ public async Task ExecScriptReturnsSuccessful()
         Assert.Empty(execResult.Stderr);
     }
 
+    [Fact]
+    [Trait(nameof(DockerCli.DockerPlatform), nameof(DockerCli.DockerPlatform.Linux))]
+    public async Task ReplicaSetStatus()
+    {
+        // Given
+        const string scriptContent = "rs.status().ok;";
+
+        // When
+        var execResult = await _mongoDbContainer.ExecScriptAsync(scriptContent)
+            .ConfigureAwait(true);
+
+        // Then
+        if (_isReplicaSet)
+        {
+            Assert.True(0L.Equals(execResult.ExitCode), execResult.Stderr);
+            Assert.Empty(execResult.Stderr);
+            Assert.Equal("true\n", execResult.Stdout);
+        }
+        else
+        {
+            Assert.Equal(1L, execResult.ExitCode);
+            Assert.Equal("MongoServerError: not running with --replSet\n", execResult.Stderr);
+        }
+    }
+
     [UsedImplicitly]
     public sealed class MongoDbDefaultConfiguration : MongoDbContainerTest
     {
@@ -80,7 +107,25 @@ public MongoDbV5Configuration()
     public sealed class MongoDbV4Configuration : MongoDbContainerTest
     {
         public MongoDbV4Configuration()
-            : base(new MongoDbBuilder().WithImage("mongo:4.4").Build())
+            : base(new MongoDbBuilder().WithImage("mongo:4.4").Build(), isReplicaSet: true) // Replica set status returns ok in MongoDB 4.4 without initialising it
+        {
+        }
+    }
+
+    [UsedImplicitly]
+    public sealed class MongoDbReplicaSetDefaultConfiguration : MongoDbContainerTest
+    {
+        public MongoDbReplicaSetDefaultConfiguration()
+            : base(new MongoDbBuilder().WithReplicaSet().Build(), isReplicaSet: true)
+        {
+        }
+    }
+
+    [UsedImplicitly]
+    public sealed class MongoDbNamedReplicaSetConfiguration : MongoDbContainerTest
+    {
+        public MongoDbNamedReplicaSetConfiguration()
+            : base(new MongoDbBuilder().WithReplicaSet("rscustom").Build(), isReplicaSet: true)
         {
         }
     }