Bind zone file backend

The BindBackend started life as a demonstration of the versatility of PowerDNS but quickly gained in importance when there appeared to be demand for a Bind 'work-alike'.

The BindBackend parses a Bind-style named.conf and extracts information about zones from it. It makes no attempt to honour other configuration flags, which you should configure (when available) using the PowerDNS native configuration.

Configuration Parameters

bind-config

Location of the Bind configuration file to parse.

bind-check-interval

How often to check for zone changes. See 'Operation' section.

bind-dnssec-db

Filename to store and access our DNSSEC metadatabase, empty for none. To slave DNSSEC-enabled domains (where the RRSIGS are in the AXFR), a bind-dnssec-db is required. This is because the PRESIGNED domain metadata is set during the zonetransfer.

bind-hybrid

Store DNSSEC keys and metadata storage in an other backend. See the hybrid BIND-mode operation

bind-ignore-broken-records

Setting this option to yes makes PowerDNS ignore out of zone records when loading zone files.

Operation

On launch, the BindBackend first parses the named.conf to determine which zones need to be loaded. These will then be parsed and made available for serving, as they are parsed. So a named.conf with 100.000 zones may take 20 seconds to load, but after 10 seconds, 50.000 zones will already be available. While a domain is being loaded, it is not yet available, to prevent incomplete answers.

Reloading is currently done only when a request for a zone comes in, and then only after bind-check-interval seconds have passed after the last check. If a change occurred, access to the zone is disabled, the file is reloaded, access is restored, and the question is answered. For regular zones, reloading is fast enough to answer the question which lead to the reload within the DNS timeout.

If bind-check-interval is specified as zero, no checks will be performed until the pdns_control reload is given.

pdns_control commands

bind-add-zone <domain> <filename>

Add zone domain from filename to PowerDNS's bind backend. Zone will be loaded at first request. Note: this does not add the zone to the bind-config file.

bind-domain-status <domain> [domain]

Output status of domain or domains. Can be one of seen in named.conf, not parsed, parsed successfully at <time> or error parsing at line ... at <time>.

bind-list-rejects

Lists all zones that have problems, and what those problems are.

bind-reload-now <domain>

Reloads a zone from disk NOW, reporting back results.

rediscover

Reread the bind configuration file (named.conf). If parsing fails, the old configuration remains in force and pdns_control reports the error. Any newly discovered domains are read, discarded domains are removed from memory.

reload

All zones with a changed timestamp are reloaded at the next incoming query for them.

Performance

The BindBackend does not benefit from the packet cache as it is fast enough on its own. Furthermore, on most systems, there will be no benefit in using multiple CPUs for the packetcache, so a noticeable speedup can be attained by specifying distributor-threads=1 in pdns.conf.

Master/slave/native configuration

Master

Works as expected. At startup, no notification storm is performed as this is generally not useful. Perhaps in the future the Bind Backend will attempt to store zone metadata in the zone, allowing it to determine if a zone has changed its serial since the last time notifications were sent out.

Changes which are discovered when reloading zones do lead to notifications however.

Slave

Also works as expected. The Bind backend expects to be able to write to a directory where a slave domain lives. The incoming zone is stored as 'zonename.RANDOM' and atomically renamed if it is retrieved successfully, and parsed only then.

In the future, this may be improved so the old zone remains available should parsing fail.

Native

PowerDNS has the concept of "native" zones that have the type native; in the BIND configuration file. These zones are neither a master (no notifies are sent) nor a slave zone (it will never be AXFR'd in). This means that the replication mechanism for these zone is not AXFR but out of band, e.g. using rsync. Changes to native zones are picked up in the same way as master and slave zones, see Operation.

Native zones in the BIND backend are supported since version 4.1.0 of the PowerDNS Authoritative Server.

note: Any zone with no type set (an error in BIND) is assumed to be native.