Operation¶
The Knot DNS server part knotd can run either in the foreground, or in the background using the -d option. When run in the foreground, it doesn’t create a PID file. Other than that, there are no differences and you can control both the same way.
The tool knotc is designed as a user front-end, making it easier to control running server daemon. If you want to control the daemon directly, use SIGINT to quit the process or SIGHUP to reload the configuration.
If you pass neither configuration file (-c parameter) nor configuration database (-C parameter), the server will first attempt to use the default configuration database stored in /var/lib/knot/confdb or the default configuration file stored in /etc/knot/knot.conf. Both the default paths can be reconfigured with --with-storage=path or --with-configdir=path respectively.
Example of server start as a daemon:
$ knotd -d -c knot.conf
Example of server shutdown:
$ knotc -c knot.conf stop
For a complete list of actions refer to the program help (-h parameter) or to the corresponding manual page.
Also, the server needs to create rundir and storage directories in order to run properly.
Configuration database¶
In the case of a huge configuration file, the configuration can be stored in a binary database. Such a database can be simply initialized:
$ knotc conf-init
or preloaded from a file:
$ knotc conf-import input.conf
Also the configuration database can be exported into a textual file:
$ knotc conf-export output.conf
Warning
The import and export commands access the configuration database directly, without any interaction with the server. So it is strictly recommended to perform these operations when the server is not running.
Dynamic configuration¶
The configuration database can be accessed using the server control interface during the running server. To get the full power of the dynamic configuration, the server must be started with a specified configuration database location or with the default database initialized. Otherwise all the changes to the configuration will be temporary (until the server stop).
Note
The database can be imported in advance.
Most of the commands get an item name and value parameters. The item name is in the form of section[identifier].name. If the item is multivalued, more values can be specified as individual (command line) arguments. Beware of the possibility of pathname expansion by the shell. For this reason, slashed square brackets or quoted parameters is advisable.
To get the list of configuration sections or to get the list of section items:
$ knotc conf-list
$ knotc conf-list 'server'
To get the whole configuration or to get the whole configuration section or to get all section identifiers or to get a specific configuration item:
$ knotc conf-read
$ knotc conf-read 'remote'
$ knotc conf-read 'zone.domain'
$ knotc conf-read 'zone[example.com].master'
Warning
The following operations don’t work on OpenBSD!
Modifying operations require an active configuration database transaction. Just one transaction can be active at a time. Such a transaction then can be aborted or committed. A semantic check is executed automatically before every commit:
$ knotc conf-begin
$ knotc conf-abort
$ knotc conf-commit
To set a configuration item value or to add more values or to add a new section identifier or to add a value to all identified sections:
$ knotc conf-set 'server.identity' 'Knot DNS'
$ knotc conf-set 'server.listen' '0.0.0.0@53' '::@53'
$ knotc conf-set 'zone[example.com]'
$ knotc conf-set 'zone.slave' 'slave2'
Note
Also the include operation can be performed. A non-absolute file location is relative to the server binary path, not to the control binary path!:
$ knotc conf-set 'include' '/tmp/new_zones.conf'
To unset the whole configuration or to unset the whole configuration section or to unset an identified section or to unset an item or to unset a specific item value:
$ knotc conf-unset
$ knotc conf-unset 'zone'
$ knotc conf-unset 'zone[example.com]'
$ knotc conf-unset 'zone[example.com].master'
$ knotc conf-unset 'zone[example.com].master' 'remote2' 'remote5'
To get the change between the current configuration and the active transaction for the whole configuration or for a specific section or for a specific identified section or for a specific item:
$ knotc conf-diff
$ knotc conf-diff 'zone'
$ knotc conf-diff 'zone[example.com]'
$ knotc conf-diff 'zone[example.com].master'
An example of possible configuration initialization:
$ knotc conf-begin
$ knotc conf-set 'server.listen' '0.0.0.0@53' '::@53'
$ knotc conf-set 'remote[master_server]'
$ knotc conf-set 'remote[master_server].address' '192.168.1.1'
$ knotc conf-set 'template[default]'
$ knotc conf-set 'template[default].storage' '/var/lib/knot/zones/'
$ knotc conf-set 'template[default].master' 'master_server'
$ knotc conf-set 'zone[example.com]'
$ knotc conf-diff
$ knotc conf-commit
Slave mode¶
Running the server as a slave is very straightforward as you usually bootstrap zones over AXFR and thus avoid any manual zone operations. In contrast to AXFR, when the incremental transfer finishes, it stores the differences in the journal file and doesn’t update the zone file immediately but after the zonefile-sync period elapses.
Master mode¶
If you just want to check the zone files before starting, you can use:
$ knotc zone-check example.com
For an approximate estimation of server’s memory consumption, you can use:
$ knotc zone-memstats example.com
This action prints the count of resource records, percentage of signed records and finally estimation of memory consumption for each zone, unless specified otherwise. Please note that the estimated values may differ from the actual consumption. Also, for slave servers with incoming transfers enabled, be aware that the actual memory consumption might be double or higher during transfers.
Reading and editing zones¶
Knot DNS allows you to read or change zone contents online using server control interface.
Warning
Avoid concurrent zone file modification, and/or dynamic updates, and/or zone changing over control interface. Otherwise, the zone could be inconsistent.
To get contents of all configured zones, or a specific zone contents, or zone records with a specific owner, or even with a specific record type:
$ knotc zone-read --
$ knotc zone-read example.com
$ knotc zone-read example.com ns1
$ knotc zone-read example.com ns1 NS
Note
If the record owner is not a fully qualified domain name, then it is considered as a relative name to the zone name.
To start a writing transaction on all zones or on specific zones:
$ knotc zone-begin --
$ knotc zone-begin example.com example.net
Now you can list all nodes within the transaction using the `zone-get` command, which always returns current data with all changes included. The command has the same syntax as `zone-read`.
Within the transaction, you can add a record to a specific zone or to all zones with an open transaction:
$ knotc zone-set example.com ns1 3600 A 192.168.0.1
$ knotc zone-set -- ns1 3600 A 192.168.0.1
To remove all records with a specific owner, or a specific rrset, or a specific record data:
$ knotc zone-unset example.com ns1
$ knotc zone-unset example.com ns1 A
$ knotc zone-unset example.com ns1 A 192.168.0.2
To see the difference between the original zone and the current version:
$ knotc zone-diff example.com
Finally, either commit or abort your transaction:
$ knotc zone-commit example.com
$ knotc zone-abort example.com
A full example of setting up a completely new zone from scratch:
$ knotc conf-begin
$ knotc conf-set zone.domain example.com
$ knotc conf-commit
$ knotc zone-begin example.com
$ knotc zone-set example.com @ 7200 SOA ns hostmaster 1 86400 900 691200 3600
$ knotc zone-set example.com ns 3600 A 192.168.0.1
$ knotc zone-set example.com www 3600 A 192.168.0.100
$ knotc zone-commit example.com
Journal behaviour¶
Zone journal keeps some history of changes of the zone. It is useful for responding IXFR queries. Also if zone file flush is disabled, journal keeps diff between zonefile and zone for the case of server shutdown. The history is stored by changesets - diffs of zone contents between two (usually subsequent) zone serials.
Journals for all zones are stored in common LMDB database. Huge changesets are split into 70 KiB (this constant is hardcoded) blocks to prevent fragmentation of the DB. Journal does each operation in one transaction to keep consistency of the DB and performance. The exception is when store transaction exceeds 5% of the whole DB mapsize, it is split into multiple ones and some dirty-chunks-management involves.
Each zone journal has own usage limit on how much DB space it may occupy. Before hitting the limit, changesets are stored one-by-one and whole history is linear. While hitting the limit, the zone is flushed into zone file, and oldest changesets are deleted as needed to free some space. Actually, twice (again, hardcoded constant) the needed amount is deleted to prevent too frequent deletes. Further zone file flush is invoked after the journal runs out of deletable “flushed changesets”.
If zone file flush is disabled, instead of flushing the zone, the journal tries to save space by merging older changesets into one. It works well if the changes rewrite each other, e.g. periodically changing few zone records, re-signing whole zone... The diff between zone file and zone is thus preserved, even if journal deletes some older changesets.
DNSSEC keys algorithm rollover¶
Algorithm rollover is a process of changing DNSSEC signing keys, where the new keys are of different algorithm. The zone signatures must never go Bogus during the process, even considering records cached in resolvers. The process is generally described in RFC 6781. Following are some hints how to implement algorithm rollover when using Knot DNS.
The prerequisite is having a zone with automatic DNSSEC signing enabled, active KSK and ZSK present. (The CSK case should work analogously, not mentioned further.) It is recommended to disable automatic key management during the rollover. Note that from the view of common key rollovers, here we must put the keys into a weird state: active, but not published. This is done by hard-setting their timers so that active < publish < retire (whereas standard rollovers have publish < active < retire).
First we need to generate new keys. They must be first used for signing, and after some period (propagation delay let’s say 1h + zone records’ TTL let’s say 1h) published. We have to preprate the timestamps carefully, using the notation ‘now+2h’ can be creepy with “now” changing between the Keymgr invokes. We then re-sign the zone just to force knotd to reload zone keys:
$ NOW=$(date +%s)
$ NOW2H=$((NOW + 7200))
$ keymgr example.com. generate algorithm=14 size=384 ksk=yes \
ready=$NOW2H active=0 publish=$NOW2H
$ keymgr example.com. generate algorithm=14 size=384 ksk=no \
ready=$NOW active=$NOW publish=$NOW2H
$ knotc zone-sign example.com.
After waiting for the keys to get published as scheduled, we may tell the parent zone operator to renew our DS record. As the KSK is in ready state, we have the CDS/CDNSKEY records in our zone. After waiting again for some propagation period, we continue with removing old KSK and putting old ZSK into active-not-published state (we must first obtain the keys’ IDs with ‘keymgr example.com. list’). We may also confirm the new KSK submission (which reloads KASP DB as a side-effect):
$ keymgr example.com. set $OLD_KSK_ID retire=now+0 remove=now+0
$ keymgr example.com. set $OLD_ZSK_ID publish=0
$ knotc zone-ksk-submitted example.com.
Finally, after one more propagation period, we remove old ZSK:
$ keymgr example.com. set $OLD_ZSK_ID retire=now+0 remove=now+0
$ knotc zone-sign example.com.
Daemon controls¶
Knot DNS was designed to allow server reconfiguration on-the-fly without interrupting its operation. Thus it is possible to change both configuration and zone files and also add or remove zones without restarting the server. This can be done with:
$ knotc reload
If you want to enable ixfr differences creation from changes you make to a zone file, enable ixfr-from-differences in the zone configuration and reload your server as seen above. If SOA‘s serial is not changed, no differences will be created.
If you want to refresh the slave zones, you can do this with:
$ knotc zone-refresh
Statistics¶
The server provides some general statistics and optional query module statistics (see mod-stats).
Server statistics or global module statistics can be shown by:
$ knotc stats
$ knotc stats server # Show all server counters
$ knotc stats mod-stats # Show all mod-stats counters
$ knotc stats server.zone-count # Show specific server counter
Per zone statistics can be shown by:
$ knotc zone-stats example.com mod-stats
To show all supported counters even with 0 value use the force option.
A simple periodic statistic dumping to a YAML file can also be enabled. See Statistics section for the configuration details.
As the statistics data can be accessed over the server control socket, it is possible to create an arbitrary script (Python is supported at the moment) which could, for example, publish the data in the JSON format via HTTP(S) or upload the data to a more efficient time series database. Take a look into the python folder of the project for these scripts.
