ClickHouse/tests/integration/test_distributed_ddl/configs/config.d/clusters.xml

<clickhouse>
<remote_servers>

    <!-- Main cluster -->
    <cluster>
        <shard>
            <internal_replication>true</internal_replication>
            <replica>
                <host>ch1</host>
                <port>9000</port>
            </replica>
            <replica>
                <host>ch2</host>
                <port>9000</port>
            </replica>
        </shard>
        <shard>
            <internal_replication>true</internal_replication>
            <replica>
                <host>ch3</host>
                <port>9000</port>
            </replica>
            <replica>
                <host>ch4</host>
                <port>9000</port>
            </replica>
        </shard>
    </cluster>

    <!-- Cluster with specified default database -->
    <cluster2>
        <shard>
            <internal_replication>true</internal_replication>
            <replica>
                <host>ch1</host>
                <port>9000</port>
                <default_database>default</default_database>
            </replica>
            <replica>
                <host>ch2</host>
                <port>9000</port>
                <default_database>test2</default_database>
            </replica>
        </shard>
        <shard>
            <internal_replication>true</internal_replication>
            <replica>
                <host>ch3</host>
                <port>9000</port>
                <default_database>default</default_database>
            </replica>
            <replica>
                <host>ch4</host>
                <port>9000</port>
                <default_database>test2</default_database>
            </replica>
        </shard>
    </cluster2>

    <!-- Cluster without replicas -->
    <cluster_no_replicas>
        <shard>
            <internal_replication>false</internal_replication>
            <replica>
                <host>ch1</host>
                <port>9000</port>
            </replica>
        </shard>
        <shard>
            <internal_replication>false</internal_replication>
            <replica>
                <host>ch2</host>
                <port>9000</port>
            </replica>
        </shard>
        <shard>
            <internal_replication>false</internal_replication>
            <replica>
                <host>ch3</host>
                <port>9000</port>
            </replica>
        </shard>
        <shard>
            <internal_replication>false</internal_replication>
            <replica>
                <host>ch4</host>
                <port>9000</port>
            </replica>
        </shard>
    </cluster_no_replicas>

</remote_servers>
</clickhouse>