Since Vert.x 4.1.1, the SQL Client provides connection creation load balancing.

You can create a pool with a list of connect options that the pool uses with a round robin policy when it needs to create a connection.

List<PgConnectOptions> servers = getListOfServers();
 
PgPool pool = PgPool.create(vertx, servers);

Load balancing is actually a helper in front of a more powerful feature:

interface Pool {
  ....
  Pool connectionProvider(Function<Context, Future<SqlConnection>> provider);
  ....
}

The connectionProvider is called by the pool when it needs to create a new connection. Here is a trivial example:

ConnectionFactory factory = new PgDriver().connectionFactory(vertx, connectOptions);
pool.connectionProvider(ctx -> {
  return factory.connect(ctx);
});

Since the provider is asynchronous, it can be used to provide dynamic pool configuration.

pool.connectionProvider(ctx -> {
  Future<PgConnectOptions> fut = retrieveOptions();
  return fut.compose(connectOptions -> {
    // Do not forget to close later
    ConnectionFactory factory = new PgDriver().connectionFactory(vertx, connectOptions);
    return factory.connect(ctx);
  });
});

Important caveat: when the connection factory becomes useless (e.g because of a new configuration) it must be closed to release its resources.

The SQL client does not provide this feature out of the box because of this caveat. It is difficult to determine when the factories need to be disposed. Instead, we expose the connectionProvider to allow applications to implement it trivially since each application knows best how and when to release the resources.