Databases

ContainerDefinition has a factory method for each supported database. The definition it returns is already configured: the image, the published port, a strong random password where the database needs one, and the wait strategies that tell when the server accepts connections. The container it creates has a GetConnectionString() method.

The connection strings point to the host address (127.0.0.1, unless the daemon runs on another machine) and the host port of the container, so call GetConnectionString after StartAsync: before, it throws an InvalidOperationException.

Redis

await using var redis = ContainerDefinition.CreateRedis().CreateContainer();
await redis.StartAsync();

var connectionString = redis.GetConnectionString(); // 127.0.0.1:<port>, for StackExchange.Redis

The connection string is host:port, the format StackExchange.Redis expects. The server has no password.

PostgreSQL

var definition = ContainerDefinition.CreatePostgreSql(ImageSource.FromRegistry("postgres:17"));
definition.Environment.Add("POSTGRES_USER", "app");
definition.Environment.Add("POSTGRES_DB", "orders");

await using var postgres = definition.CreateContainer();
await postgres.StartAsync();

var connectionString = postgres.GetConnectionString(); // Host=127.0.0.1;Port=<port>;Username=app;Password=<password>;Database=orders

• The connection string is in the Npgsql format. It reads the user, the password and the database from the POSTGRES_USER, POSTGRES_PASSWORD and POSTGRES_DB variables of the definition, the variables the image uses to initialize the server. The user defaults to postgres and the database to the name of the user.
• The password is generated; set Password to choose it.

MongoDB

var definition = ContainerDefinition.CreateMongoDb();
definition.RootUsername = "admin"; // "root" by default; the password is generated

await using var mongo = definition.CreateContainer();
await mongo.StartAsync();

var connectionString = mongo.GetConnectionString(enableJournaling: true); // mongodb://admin:<password>@127.0.0.1:<port>/?authSource=admin&j=true

• RootUsername and RootPassword set the MONGO_INITDB_ROOT_USERNAME and MONGO_INITDB_ROOT_PASSWORD variables. The user is root and the password is generated unless you set them.
• The connection string authenticates against the admin database. Journaling is off (j=false) unless you pass enableJournaling: true.

SQL Server

await using var sqlServer = ContainerDefinition.CreateSqlServer().CreateContainer();
await sqlServer.StartAsync();

var connectionString = sqlServer.GetConnectionString(); // Server=127.0.0.1,<port>;Database=master;User Id=sa;Pwd=<password>;...

• The definition accepts the end-user license agreement of the image (ACCEPT_EULA=Y) and generates a password that meets the complexity rules of SQL Server. Set SaPassword to choose it.
• The connection string logs in as sa to the master database, with Encrypt=True and TrustServerCertificate=True, since the server uses a self-signed certificate.
• Microsoft publishes the SQL Server image for x64 only: on an arm64 machine, it only runs where the runtime emulates x64.

Choose the image and the settings

Each factory method has an overload that takes the image, to pin another version. The definition is a regular ContainerDefinition: add environment variables, mounts or wait strategies before you create the container. This example shows all four databases, with the passwords set explicitly:

await using var redis = ContainerDefinition.CreateRedis().CreateContainer();
await redis.StartAsync();
var redisConnectionString = redis.GetConnectionString(); // 127.0.0.1:<port>

var postgresDefinition = ContainerDefinition.CreatePostgreSql(); // or CreatePostgreSql(ImageSource.FromRegistry("postgres:16"))
postgresDefinition.Environment.Add("POSTGRES_DB", "mydb");
// Optional: override the generated strong random password
postgresDefinition.Password = "my-password";
await using var postgres = postgresDefinition.CreateContainer();
await postgres.StartAsync();
var postgresConnectionString = postgres.GetConnectionString(); // Host=127.0.0.1;Port=<port>;Username=postgres;Password=<password>;Database=mydb

await using var mongo = ContainerDefinition.CreateMongoDb().CreateContainer();
await mongo.StartAsync();
var mongoConnectionString = mongo.GetConnectionString(); // mongodb://root:<password>@127.0.0.1:<port>/?authSource=admin&j=false

var sqlDefinition = ContainerDefinition.CreateSqlServer();
// Optional: override the generated strong random password
sqlDefinition.SaPassword = "Abcdef1!Abcdef1!";
await using var sqlServer = sqlDefinition.CreateContainer();
await sqlServer.StartAsync();
var sqlServerConnectionString = sqlServer.GetConnectionString(); // Server=127.0.0.1,<port>;Database=master;User Id=sa;Pwd=<password>;Encrypt=True;TrustServerCertificate=True;Connection Timeout=30

The connection strings are built with a connection string builder, so a password that contains ; or = still works.

Other databases and services

Any other service is a ContainerDefinition with its image, its port and a wait strategy. See Configuring a container and Wait strategies.