Connect to ClickHouse

ntopng connect sto clickhouse using two different connections:

  • Flows are imported into the database in batch mode using clickhouse-client. This is because in columnary databases this is the most efficient technique for importing large volumes of data.
  • MySQL connection to insert alerts (theoretically this is not a large capacity actovoty so avoiding batch inserts reduces latency) and perform queries.

In order to connect ntopng to ClickHouse use option -F. The format of this option is the following



clickhouse-cluster;<host[@port]|socket>;<dbname>;<user>;<pw>;<cluster name>


  • <host[@port]|socket> Specifies the database host or a socket file. By default, port 9000 is used for the connection via clickhouse-client. To use a different port, specify it with @port. The host can be a symbolic name or an IP address. By default ntopng connects in clear text, this unless you want to do it over TLS and in this case you need to append a ‘s’ after the port. Example Please see later in this pare more information about TLS connections.
  • <dbname> Specifies the name of the database to be used and defaults to ntopng
  • <user> Specifies an user with read and write permissions on <dbname>
  • <pw> Specifies the password that authenticates <user>
  • <cluster name> Specifies the name of the ClickHouse cluster <user>

If you use a stand-alone ClickHouse database you need to use -F clickhouse;.... whereas with a cluster you need to use -F clickhouse-cluster;....


To connect ntopng and ClickHouse, both running on the same machine, the following line can be used

./ntopng -F="clickhouse;;ntopng;default;default"

In the example above, is used to connect using IPv4 (using the symbolic string localhost could resolve to an IPv6 address). A user default, identified with password default, with read and write permissions on database ntopng is indicated as well. As shortcut you can use -F clickhouse for F="clickhouse;;ntopng;default;default"

The above example with a ClickHouse cluster would be:

./ntopng -F="clickhouse-cluster;;ntopng;default;default;ntop_cluster"

What’s Stored in ClickHouse

ntopng stores both historical flows and alerts in ClickHouse.

IPv4 and IPv6 flows are stored in table flows. A column INTERFACE_ID is used to identify the interface on which the flow was seen, this is useful ntopng is monitoring multiple interfaces (see -i).

Alerts are stored in several tables, all ending with suffix _alerts. The table prefix indicates the alert family, e.g. host_alerts table contains alerts for hosts, flow_alerts table contains alerts for flows, and so on.

For more information, check the ntopng database schema.

TLS Connection

In order to connect ntopng with ClickHouse using a secure TCP connection, first, create the server certificate with the following command:

openssl req -subj "/CN=localhost" -new -newkey rsa:2048 -days 365 -nodes -x509 -keyout /etc/clickhouse-server/server.key -out /etc/clickhouse-server/server.crt

This command generates a server certificate for secure communication between ntopng and ClickHouse, establishing a secure TCP connection.


To enable the ClickHouse user to use the server.crt and server.key files, it is necessary to change their owner. Run the following command as a superuser to grant the required permissions:

chown clickhouse:clickhouse /etc/clickhouse-server/server.key /etc/clickhouse-server/server.crt

Open the ClickHouse config.xml file and uncomment the following lines:

  • <!--<tcp_port_secure>9440</tcp_port_secure>-->
  • <!--<certificateFile>/etc/clickhouse-server/server.crt</certificateFile>-->
  • <!--<privateKeyFile>/etc/clickhouse-server/server.key</privateKeyFile>-->

Restart ClickHouse.

Start ntopng using the -F option, but in this case, it is mandatory to indicate the database port with an s at the end of it.


For example:

./ntopng -F="clickhouse;;ntopng;default;default`

ClickHouse Is Eating All My Disk/Memory !

The defaut ClickHouse package configuration is not optimizes for reducing disk and memory usage. In order to avoid this problem please refer to this guide that explain in detail how to optimize the fatabase configuration.