# DynDB (Dynamic Database)

DynDB is an extension to BIND 9 which, like DLZ (see dlz-info), allows zone data to be retrieved from an external database. Unlike DLZ, a DynDB module provides a full-featured BIND zone database interface. Where DLZ translates DNS queries into real-time database lookups, resulting in relatively poor query performance, and is unable to handle DNSSEC-signed data due to its limited API, a DynDB module can pre-load an in-memory database from the external data source, providing the same performance and functionality as zones served natively by BIND.

A DynDB module supporting LDAP has been created by Red Hat and is available from https://fedorahosted.org/bind-dyndb-ldap/.

A sample DynDB module for testing and developer guidance is included with the BIND source code, in the directory `bin/tests/system/dyndb/driver`.

A DynDB database is configured with a `dyndb` statement in `named.conf`:

        dyndb example "driver.so" {
            parameters
        };

The file `driver.so` is a DynDB module which implements the full DNS database API. Multiple `dyndb` statements can be specified, to load different drivers or multiple instances of the same driver. Zones provided by a DynDB module are added to the view's zone table, and are treated as normal authoritative zones when BIND is responding to queries. Zone configuration is handled internally by the DynDB module.

The `parameters` are passed as an opaque string to the DynDB module's initialization routine. Configuration syntax will differ depending on the driver.

For guidance in implementation of DynDB modules, the directory `bin/tests/system/dyndb/driver`. contains a basic DynDB module. The example sets up two zones, whose names are passed to the module as arguments in the `dyndb` statement:

        dyndb sample "sample.so" { example.nil. arpa. };

In the above example, the module is configured to create a zone "example.nil", which can answer queries and AXFR requests, and accept DDNS updates. At runtime, prior to any updates, the zone contains an SOA, NS, and a single A record at the apex:

     example.nil.  86400    IN      SOA     example.nil. example.nil. (
                                                   0 28800 7200 604800 86400
                                           )
     example.nil.  86400    IN      NS      example.nil.
     example.nil.  86400    IN      A       127.0.0.1

When the zone is updated dynamically, the DynDB module will determine whether the updated RR is an address (i.e., type A or AAAA) and if so, it will automatically update the corresponding PTR record in a reverse zone. (Updates are not stored permanently; all updates are lost when the server is restarted.)