Provided by: gdnsd_3.8.2-1build2_amd64 
NAME
gdnsd.config - gdnsd configuration file
SYNOPSIS
options => {
tcp_timeout => 15 ; zonefile-style comment
listen => [ 127.0.0.1, 192.0.2.1 ]
}
# shell-style comment
service_types => {
foosvc => { plugin => http_status, vhost => www.example.com, url_path => "/checkme" }
barsvc => $include{bar-svc.cfg}
$include{other-services.cfg}
}
plugins => {
null => {}
}
DESCRIPTION
This man page describes the syntax of the primary gdnsd configuration file. The primary
config file is always the the file named config in the configuration directory. The
default configuration directory is /etc/gdnsd, but this can be overridden by the "-c"
commandline option.
The lower-level syntax and structure of the configuration language is described in detail
at the end of this document, but it should be fairly intuitive from the example above. It
is effectively a generic data structure language allowing arbitrarily-nested ordered
hashes, ordered arrays, and scalar values. Double-quotes are used to quote scalars
containing whitespace or various ambiguous metacharacters.
The top-level implicit hash of a gdnsd configuration file allows only 3 legal keys:
options, service_types, and plugins.
Any of them which are present must have a Hash as their value.
All of them are optional, as is the configuration file itself. If you're happy with an
all-default configuration, you can simply not have a config file at all.
OPTIONS HASH
These options control the overall behavior of gdnsd(8).
zones_default_ttl
Integer seconds, default 86400. This is the global default time-to-live for any
record in any zonefile. It can be overridden with a more specific default within zone
files themselves via the $TTL directive (see gdnsd.zonefile(5)).
max_ttl
Integer seconds, default 3600000 (~42 days), range 3600 - 268435455 (2^28-1, ~8.5
years). This is the global maximum TTL. Any TTL found in a zone which exceeds this
value will be clamped to this value with a warning. Note that the default maximum
value is what the Internet's root nameservers currently use for A-record TTLs, and
those are arguably the most stable records in the whole system. It's hard to imagine
good reasons to raise this value in practice.
min_ttl
Integer seconds, default 5, range 0 - 86400 (1 day). This is the global minimum TTL.
Any TTL found in a zone which is below this value will be clamped to this value with a
warning, including the minimum TTLs of DYN[AC] records and SOA ncache TTLs. This
value must be less than or equal to max_ttl.
max_ncache_ttl
Integer seconds, default 10800, range 10 - 86400. This is the global maximum for the
SOA negative-cache TTL field. Values above this will be clamped with a warning. This
value must be greater than or equal to min_ttl.
dns_port
Integer port, 1-65535, default 53. This is the global default port number for DNS
listener addresses which do not specify port numbers themselves.
listen
The listen option specifies the socket addresses the server listens on for DNS
requests.
A listen-address specification is an IP (v4 or v6) address specified as a numeric
string with standard formatting (anything numeric that getaddrinfo() supports on your
platform), optionally followed by a colon and a port number. If no port number is
specified, it defaults to the value from "dns_port", which defaults to 53.
Due to various parsing ambiguities, if you wish to specify a non-default port number
for an IPv6 listen address, you will have to enclose the address part in square
brackets, and then enclose the entire string in double-quotes.
The structure of the listen option as a whole can take one of three basic forms. In
its simplest form, it is just a single listen-address specification as a string, such
as:
options => { listen = 192.0.2.1 }
It can also take the form of an array of such addresses, as in:
options => {
listen = [
192.0.2.1,
192.0.2.2,
2001:DB8::1,
"[2001:DB8::1234]:53035",
]
}
It can also be a hash where the keys are listen addresses, and the values are per-
address options, as in:
options => {
listen => {
192.0.2.1 => {
tcp_timeout = 15
},
192.0.2.2:53035 => {
udp_threads = 5
},
}
}
The per-address options (which are identical to, and locally override, the global
option of the same name) are "tcp_threads", "tcp_timeout", "tcp_clients_per_thread",
"tcp_fastopen", "udp_threads", "udp_rcvbuf", and "udp_sndbuf".
Finally, it can also be set to the special string value "any", as in:
options => { listen => any }
In this mode, the daemon will listen on the "dns_port" port (default 53) on the IPv4
and IPv6 "ANY" addresses 0.0.0.0 and "::". gdnsd's "ANY"-address sockets should
correctly handle sending outgoing datagrams via the interface they were received on
with a source address matching the destination address of the request.
Production configurations should always explicitly define their "listen" option, as
the default could be subject to breaking changes in major version upgrades. The
current default is the "any" behavior above.
tcp_threads
Integer, default 2, min 1, max 1024. This is the number of separate TCP listening
sockets and corresponding listener threads that will be created for each DNS listener
address. On a multi-core host, increasing this parameter (up to at most a very small
multiple of the CPU core count) may increase overall performance.
udp_threads
Exactly like "tcp_threads", but for UDP sockets per DNS listening address.
tcp_clients_per_thread
Integer, default 256, min 16, max 65535. This is maximum number of tcp DNS
connections gdnsd will allow to occur in parallel per listening tcp thread. When this
limit is reached by a new incoming connection, the longest-idle of the existing
connections will be closed immediately in exchange for it.
You can monitor the "tcp.close_s_kill" stat to see if such closes are happening due to
reaching the limit, which should be avoided if possible. The code is designed to be
resilient (at least answer one legitimate request per legitimate connection) even in
the face of misbehaving (e.g. slow-read/write) connection overloads on Linux, and on
BSDs with "SO_ACCEPTFILTER" and the appropriate kernel modules ("accf_dataready"
and/or "accf_dns") loaded (there will be a non-fatal error log output on startup if
they aren't).
Note that socket addresses map 1:m to threads (that is, each thread gets a separate
"SO_REUSEPORT" instantiation of a given logical socket), and thus the total client
limit for connecting to a given socket address would be "tcp_clients_per_thread *
tcp_threads", but it's up to the operating system to balance connections, and it may
use simple connection tuple hashing or simple round-robin, neither of which may
guarantee very even distribution.
tcp_timeout
Integer seconds, default 37, min 5, max 1800.
This determines the client-side idle timeout for TCP connections, which is sent by the
server to applicable clients supporting signalling mechanisms like RFC 7828 EDNS TCP
Keepalive or RFC 8490 DNS Stateful Operations (DSO).
There is a corresponding server-side timeout which determines when gdnsd will give up
on a client it believes to be delinquent (one that keeps a connection open too long
without honoring any signalled client-side idle timeout). The server-side timeout is
double the client timeout (which equates to a default of 74, min 10, max 3600).
Note that in the common/typical case of well-behaved clients and connections, on a
Linux server (where we use TCP_DEFER_ACCEPT) or a BSD server supporting the "dnsready"
or "dataready" accept filters, when a new connection arrives we immediately receive
the first request and fire back the response without any opportunity for delays that
count as idle time, without re-entering the general eventloop where idle time is
processed or other new connections could arrive.
The idleness of a client is only reset after it completes each full transaction (send
us a full request, and our full response makes it into at least the local write
buffer). Inability to immediately write a full response into the server's local TCP
buffers (generally because the client has a too-small receive window and/or is not
ACKing several previous replies) causes immediate connection termination. Well-
behaved client connections which don't stall out midway through a transaction only
become idle connections (subject to termination for idleness) during inter-transaction
idle periods after their first transaction, and for not-so-well-behaved clients the
idle timer helps control the impact of patterns similar to slow-read/write attacks.
The server will send edns TCP keepalive information to clients with all responses
where it is legal (request used EDNS over TCP, and DSO is not yet established). The
timeout value will be sent with the fixed value that is configured here until the
server begins shutting down, at which point the zero value is sent in such responses
in an attempt to get clients to cleanly close.
Clients which establish DSO via the Keepalive TLV will get the same client-side
timeout sent to them as the DSO Inactivity timeout, with the DSO KeepAlive interval
set to Infinite (this means we don't request the client to ever send artificial
keepalive pings, and our client-side timeout applies to the interval between real DNS
request transactions in the session). DSO clients will also get better and more-
timely information when the server is shutting down or being replaced (we can push
immediate DSO unidirectional messages towards them asking that they close their
session gracefully).
disable_tcp_dso
Boolean, default false. This disables RFC 8490 DNS Stateful Operations (DSO) support
for TCP threads.
Probably the only good reasons to disable would be finding interop issues or
misbehaviors in this new code and/or standard, as otherwise it offers a superior
mechanism for managing stateful client connections versus the previous best available
solution (RFC 7828 EDNS TCP Keepalive).
tcp_backlog
Integer, min 0, default 0, max 65535. This sets the "backlog" argument of the
listen() call for TCP listening sockets. The exact effects of this varies by OS
implementation, and it can also interact with features like "TCP_DEFER_ACCEPT" and
"SO_ACCEPTFILTER". If left at (or set to) the default value of zero, the compile-time
constant "SOMAXCONN" from the operating system will be used, which tends to be
reasonable for most use-cases.
tcp_fastopen
Integer, default 256, min 0, max 1048576. If set to a non-zero value, declares a TCP
Fastopen queue size and enables the feature. TCP Fastopen allows clients who have
connected to the server at least once before to send initial data (in our case, their
first DNS request) at the same time as their initial SYN, shaving off the round trip
delays of the handshake on reconnect. This is recommended, but may require OS-level
support and/or configuration tuning, and in the case of multiple servers behind a
loadbalancer or anycast pool, may also require administrative coordination of the
server-side secret TFO key.
tcp_proxy
Boolean, default false. This TCP option is only supported inside the per-address
options of a specific listener address in the hash form of the "listen" option, not as
a global option.
Addresses for which the option is enabled only accept PROXY requests, cannot use port
number 53, do not spawn corresponding UDP listeners, and do not accept UDP-related
options. We support both version 1 and 2 of the PROXY protocol as defined in
<https://www.haproxy.org/download/1.8/doc/proxy-protocol.txt>, and only accept TCPv4,
TCPv6, and PROXYv2's "LOCAL".
The source IP passed to gdnsd over the PROXY protocol will be used as the connection
source address for all logical purposes, including e.g. GeoIP lookup fallbacks in the
absence of edns-client-subnet. Once the initial PROXY header is parsed successfully,
the connection is treated exactly as any other TCP connection for the remainder of its
life.
It is not recommended to expose PROXY listeners to public traffic; they should be
confined to localhost or to addresses which are not reachable outside of your
infrastructure due to firewalling, etc. This option is primarily intended to test
encrypted transports using external daemons proxying into gdnsd. If using it for some
other generic loadbalancing without crypto, padding should be disabled via "tcp_pad"
below.
PROXY connections increment all of the same stat counters as regular TCP connections,
and also add two new proxy-specific ones:
tcp.proxy: count of received connections on PROXY listeners (also
increments the normal tcp.conns stat).
tcp.proxy_fail: count of received PROXY connections which are
closed early for failing to send a PROXY header
the server parses and likes (also increments
tcp.close_s_err)
Example listen config:
options => {
listen => {
0.0.0.0 => { ... } # normal UDP+TCP on port 53
:: => { ... } # normal UDP+TCP on port 53 for IPv6
127.0.0.1:53035 => { tcp_proxy => true, ... }
}
}
tcp_pad
Boolean, default false for normal TCP listeners, default true for "tcp_proxy"
listeners (see above). This TCP option is only supported inside the per-address
options of a specific listener address in the hash form of the "listen" option, not as
a global option.
If enabled (by default for the "tcp_proxy" case), a response to any request which
carries an EDNS OPT RR will be padded using the EDNS Padding option to a multiple of
468 bytes as recommended in RFC 8467. This should only be enabled if the TCP
connections to a listener are encrypted by a proxy, which is the intended use-case for
"tcp_proxy" above. You may wish to enable this manually if proxying encrypted
requests via a daemon that doesn't do the PROXY protocol, and you may wish to disable
it on "tcp_proxy" listeners if the other daemon isn't providing a crypto wrapper.
udp_rcvbuf
Integer, min 4096, max 1048576, default 0. If set to a non-zero value, this value
will be used to set the "SO_RCVBUF" socket option on the UDP listening socket(s),
otherwise we leave the OS defaults alone.
udp_sndbuf
Integer, min 4096, max 1048576, default 0. If set to a non-zero value, this value
will be used to set the "SO_SNDBUF" socket option on the UDP listening socket(s),
otherwise we leave the OS defaults alone.
tcp_control
DANGER - Exposing the control socket over TCP is dangerous. The control socket server
code is not designed to be robust against arbitrary attack traffic, and does not have
any authentication or encryption. Listen addresses defined here should be well-
protected and confined by network firewall policies to internal, privileged clients,
and should definitely not be exposed on the public Internet.
This specifies one or more secondary TCP listen addresses for control socket
connections (alongside the required primary UNIX domain socket), which must be
explicitly configured if desired. It is similar to listen above in that it accepts
either a single address spec, an array of address specs, or a hash whose keys are
address specs and whose values are address-specific options. All address specs must
include an explicit address and non-zero port number.
The only two address-specific options are "chal_ok" and "ctl_ok", which are booleans
defaulting to false. By default, a TCP control socket is restricted to read-only
operations ("gdnsdctl status", "gdnsdctl stats", and "gdnsdctl states"). "chal_ok"
allows ACME Challenge operations on the socket ("gdnsdctl acme-dns-01" and "gdnsdctl
acme-dns-01-flush"). "ctl_ok" allows daemon control commands on the socket ("gdnsdctl
reload-zones" and "gdnsdctl replace"). The "gdnsdctl stop" command isn't allowed over
TCP at all.
The standard unix control socket is also used for some inter-daemon coordination and
resource handoff during replacements, which cannot be supported over the TCP variant.
Examples:
options => { tcp_control => 127.0.0.1:885 } # read-only ops only
options => { tcp_control => [ 127.0.0.1:885, 127.0.0.2:885 ] } # ditto
options => { tcp_control => {
127.0.0.1:885 => {} # readonly
127.0.0.1:886 => { chal_ok => true } # allows challenge stuff
127.0.0.1:887 => { ctl_ok => true } # allows daemon control
127.0.0.1:888 => { chal_ok => true, ctl_ok => true } # allows both
}}
The "gdnsdctl" client has an option "-s" for specifying a TCP socket to connect to for
use with "tcp_control" sockets, in which case it does not even attempt to parse the
server configuration to find the normal unix socket path.
zones_strict_data
Boolean, default "false"
If false (the default), reporting of many less-serious errors in zone data are emitted
as mere logged warnings, and the zone data is still loaded and served.
If this is set to true, such warnings will be upgraded and treated the same as the
more-serious class of zone data errors which prevent successful loading of zone data.
zones_rfc1035_threads
Integer, default 2, min 1, max 1024. When the standard RFC1035 zone files are
(re-)loaded, up to this many ephemeral threads will be spawned in parallel to help
load and parse them faster.
The way the work is divided among the threads is relatively naive: As the zones
directory on the filesystem is scanned for zone filenames, the names are divided
evenly into N separate work lists (one per thread), and then the threads are all
spawned and work on their own fixed lists in parallel, with the final splicing of the
zone data into the root tree happening serially in the main zones thread as each
worker thread finishes. In the case that the total count of zonefiles is less than
the configured thread count, the excess threads are not spawned.
This simple strategy tends to work well for large counts of zonefiles where the per-
zonefile parsing costs are roughly even, but in cases where a minority of zonefiles
take much longer to parse than others, it will not always result in a very "fair"
outcome (some threads may run much longer than others).
Note that in general, improving the I/O performance of reading the zonefiles from disk
(e.g. put them on an SSD) tends to help more than the parallelization here does,
although both together is even better!
lock_mem
Boolean, default false. Causes the daemon to do mlockall(MCL_CURRENT|MCL_FUTURE),
which effectively locks all daemon memory into RAM, unable to be swapped. Possibly
helpful in some production cases to ensure swap-in doesn't affect DNS latency.
You'll need to ensure the ulimit for locked memory is sufficient large (e.g.
"infinity") to avoid process death.
disable_text_autosplit
Boolean, default false. On the wire, "TXT" records are encoded as discrete chunks of
up to 255 characters per chunk. The relevant RFCs state that multiple chunks should
be treated by clients as if they are concatenated. That is to say, it should make no
difference to a client whether the "TXT" data is sent as two 16-byte chunks or one
32-byte chunk.
Ordinarily, you may specify chunk(s) of a "TXT" record in gdnsd zonefiles as a string
of any size up to the legal length (just short of 16K in practice), and gdnsd will
auto-split the data into 255-byte chunks for transmission over the DNS protocol
correctly. If you choose to manually break up your TXT record into multiple strings
in the zonefile, gdnsd also honors these boundaries and will not attempt to merge them
into larger chunks where possible.
If you set this option to true, the auto-splitting behavior is disabled, and any
single character string specified in a zonefile as part of a "TXT" record which is
larger than 255 bytes will be considered a syntax error.
max_edns_response
Integer, default 1232, min 512, max 16384. This is the maximum size of a UDP edns
response to a client over IPv4, acting as a cap on the edns buffer size advertised by
the client in its request.
It is recommended that you do not raise this value from the default for a server
facing the public Internet.
Setting this in the ~4-16K range might be desirable if you have large response RR-sets
and are willing to tolerate some fragmentation, especially in a private network where
a larger path MTU (e.g. ~9K for ethernet jumbo frames) can be guaranteed.
The option obviously has no pragmatic effect if you do not have large response
datasets in your zones in the first place.
max_edns_response_v6
Integer, default 1232, min 512, max 16384.
As above for UDP edns responses over IPv6. Once again, raising this above its default
value is not recommended for a public-facing server.
edns_client_subnet
Boolean, default true. Enables support for the edns-client-subnet option from RFC
7871. gdnsd only includes this EDNS option in responses to queries which also
contained the option. In the case of normal responses from static zone data, the
scope mask will be set to zero. Dynamic response plugins have access to the query's
EDNS client-subnet data, and have full control over the response scope mask.
If the option is set to false, gdnsd will ignore the option in queries, never set it
in its responses, and plugins will not have access to any data provided by any ignored
edns-client-subnet option in queries.
Of the included standard plugins only "reflect" and "geoip" make use of edns-client-
subnet information. The rest will leave the scope mask at zero as normal for client-
location-agnostic static data.
chaos_response
String, default "gdnsd". When gdnsd receives any query with the class "CH" ("Chaos"),
as opposed to the normal "IN" ("Internet"), it will return a single response record of
class "CH" and type "TXT", which contains the string defined here. This is something
like BIND's version reporting, which responds to "version.bind" queries in the "CH"
class, and is what a client will see if they use such a query against a gdnsd server.
acme_challenge_ttl
Integer seconds, range 60-3600, default 600. For temporary ACME DNS-01 challenge data
added via "gdnsdctl acme-dns-01 ...", this sets the time until the TXT records auto-
expire from the server and disappear.
See the gdnsdctl(8) documentation about "acme-dns-01" for more details.
acme_challenge_dns_ttl
Integer seconds, range 0-3600, default 0. For temporary ACME DNS-01 challenge data
added via "gdnsdctl acme-dns-01 ...", this sets the DNS TTL value which is used in
response TXT RRs.
In previous versions, the DNS TTL value mirrored the expiry TTL from
"acme_challenge_ttl" above. However, this (non-zero DNS TTLs for these records in
general) has lead to confusing issues in the real world with ACME servers under
certain conditions.
Note that static zonefile RRs with "_acme-challenge" as their leading label are also
forced to this TTL regardless of the zonefile-level explicit TTL, to avoid cases of
mixed TTLs when mixing static and dynamic records in server outputs.
nsid
String, no default, 2-256 chars in length. Character count must be even, and all
characters must be ASCII hex digits. This encodes up to 128 bytes of arbitrary binary
data chosen by the administrator and serves it in the EDNS NSID (RFC 5001) option data
of all response packets. The NSID is obviously not emitted to clients unless they
request it via EDNS, and is not emitted at all unless this option is specified
explicitly. This is intended to help with the identification of specific servers when
multiple servers are part of an anycast or loadbalancer pool.
nsid_ascii
String, no default, 1-128 chars of printable ASCII characters. This is an convenience
alternative to "nsid" above, allowing the binary NSID data to be configured with the
bytes of a printable ASCII string up to 128 bytes in length. Only one of "nsid" or
"nsid_ascii" may be specified.
experimental_no_chain
Boolean, default true.
If set to true (the default), when a query for any RR type encounters a "CNAME" RR in
the zone data, the behavior of the server will be as if the queried type was "CNAME".
This implies no chasing of the target (right-hand-side) name to emit any further
answer-section records or delegations related to the target, even if they exist in the
local data of the same zone.
This option is likely to become the fixed behavior (no option to disable) in a future
release. If this new default behavior causes a problem, you can (for now!) set the
option to false to revert to the traditional behavior of emitting chained multi-RR
responses for zone-local CNAMEs as a workaround. Please file a bug report if so,
otherwise we'll have no feedback to go on!
This behavior is desirable for a few reasons:
RFC 7871 (edns-client-subnet) actually recommends it for at least subnet
differentiated responses, because otherwise it's ambiguous which of the multiple
answer-section records the subnet scoping applies to, and caches invariably have to
take a pessimistic view and subnet-fragment cache entries pointlessly. This is the
most-compelling rationale, and it has impact on what kind of efficient geodns setups
can work at all for certain use-cases.
It also adheres to the general principle of minimal responses we adhere to elsewhere
(caches may have the target cached already anyways), and it helps minimize response
sizes (reduce reflection, and esp helpful for DNSSEC in the future).
Also, if this were the fixed behavior of the server, rather than configurable, it
would significantly simplify the code and make lookups more efficient (these gains are
not realized by the experimental optional version).
However, it's also RFC-questionable. The original RFC1034 algorithms ask that
authoritative servers complete local CNAME chains from local data (which this
violates), but also requires recursors to complete them remotely (which makes this
work, and which most do now, but historically some older implementations implicitly
relied on the authserver doing it). RFC 2308 also touches on this topic, and the
TL;DR there is that recursors can tell our incomplete responses from actual negative
"No Data" responses about the next name in the chain by the fact that we don't emit an
SOA record in the auth section.
Update 2020-11: this has now been tested pretty widely on the Internet (by a major
site with a global audience of millions), for a very long time (nearly two years), and
there has been no evidence so far of breakage or failure reports from real users.
disable_cookies
Boolean, default false. Disables support for RFC 7873 EDNS Cookies. Not recommended,
as these cookies provide a layer of defense against both off-path response forgery and
amplification attacks. One possible legitimate reason to disable cookies would be if
gdnsd is operating in a mixed set of loadbalanced/anycasted auth servers and some of
the other servers do not support cookies, or use different algorithms than gdnsd. Our
cookie support is fairly efficient; there shouldn't be any major performance reason to
disable it.
max_nocookie_response
Integer bytes, default zero (disabled), range 128-1024. If this parameter is set to a
non-zero value, all UDP responses will be limited to this many bytes unless the query
presents a valid EDNS Cookie that the server recognizes as its own. Responses which
fail this check (UDP with no valid cookie and larger than this length) will be
truncated fully (no response RRs) and the TC-bit will be set, asking the client to
retry over TCP.
This is intended to limit the ability of attackers to use your server as a reflection
source for amplification attacks, as valid cookies give some reasonable guarantee that
the query packet source address wasn't forged. It should be pretty safe to set this
at least as low as 512, and that may become the default setting in some future
version.
cookie_key_file
String, default undefined. When this is defined, the file's contents are read as the
persistent primary key value for generating EDNS Cookie responses.
If the file exists, it must be readable by the daemon, and it must contain 32 bytes of
binary data. Failure to properly read a key file defined here is fatal at startup.
Permissions should be set with care, so that other unprivileged users of the system
cannot read the key.
Note that the contents are considered binary data and are used directly as secret key
input to crypto algorithms, and thus they should be generated securely with high
entropy and indistinguishable from random bytes. It is recommended the file's
contents be generated with an RNG outputting 32 random binary bytes, e.g.: "dd
if=/dev/urandom of=cookie.key bs=32 count=1".
The keyfile's contents don't have to be changed on any sort of fixed or frequent
schedule to maintain security. Treat it like any other long-term secret value and
make new ones once in a blue moon just out of an abundance of caution, or if you
believe the previous key material may be compromised. The daemon must be replaced or
restarted to put the new key into effect, and this will abruptly invalidate
outstanding cookies clients may be holding that were generated with previous keys.
The primary reason to define "cookie_key_file" to your own pathname and key contents
is to have synchronized cookie keys across an anycasted or otherwise loadbalanced set
of servers, so that they all agree on server cookies.
If this file is not defined, then the daemon manages the cookie primary key value
automatically. Under automatic management of the key, it will attempt to read a key
from /run/gdnsd/cookie.autokey at startup. If that doesn't work, it will generate a
new random key in memory and attempt to write it to the same path for consumption by
future daemons. If both reading an old automatic key and writing the new one fail, a
non-fatal error will be logged, and the new randomly-generated key exists only in
daemon memory and will not persist across future daemon replace or restart cycles.
Note that in common Linux/systemd installations, the run directory will be wiped on OS
reboots and a fresh key will be generated on the next daemon startup. As with a
manually-defined "cookie_key_file", any time the automatic key must be regenerated,
this will invalidate all outstanding server cookies held by clients.
run_dir
String, defaults to /run/gdnsd. This is the directory which the daemon owns as its
run directory.
It will create this directory or modify the permissions of an existng one on startup.
If it does not exist and cannot be created, or the permissions cannot be set to
acceptable values (possibly because the existing directory is owned by a different uid
than the daemon is currently running as), the daemon will not start.
The contents of this directory are private to the daemon and shouldn't be interfered
with. This can live on a filesystem that's volatile across reboots, and doesn't
require much disk space.
The daemon's control socket and lock files live here.
state_dir
String, defaults to /var/lib/gdnsd. This is the directory which the daemon owns as
its state directory.
It will create this directory if necessary at startup. If it does not exist and
cannot be created, the daemon will not start.
The contents of this directory belong to the system administrator and are used to
communicate persistent, stateful information to the daemon. This should live on a
filesystem which is preserved across reboots.
The admin_state file lives here.
SERVICE_TYPES
service_types is used in conjunction with certain gdnsd plugins. If you are not using
such a plugin, you can safely ignore this section and omit it from your configuration.
The service_types hash contains generic definitions for how to monitor a given types of
service, independently of any specific address or hostname for that service.
There are two trivial service_types internally defined as the names "up" and "down", which
do no actual monitoring and simply set the monitored state permanently "UP" or "DOWN".
"up" is the default service_type when no service_type is specified.
Within the definition of a service_type there are several generic parameters related to
timing and anti-flap, as well as plugin-specific parameters that vary per plugin.
A service type does not, however, specify a name or address for a specific instance of a
service. Those would occur on a per-address basis in a resolving plugin's configuration
down in the "plugins" stanza, and the plugin's configuration would then reference a named
service type to be used when monitoring said address.
A service monitored through these mechanisms is always in either the "UP" or "DOWN" state
at runtime from a monitoring perspective. The "UP" state is maintained in the face of
intermittent or isolated failures until the anti-flap thresholds are crossed and the state
moves to "DOWN".
Any services monitored for plugins also have their state reported alongside the standard
gdnsd statistics report, served by the built-in HTTP server (default port is 3506).
The following are the generic parameters for all service_types:
up_thresh
Integer, default 20, min 1, max 65535. Number of monitoring requests which must
succeed in a row without any failures to transition a given resource from the "DOWN"
state to the "UP" state.
ok_thresh
Integer, default 10, min 1, max 65535. See below.
down_thresh
Integer, default 10, min 1, max 65535. The "ok_thresh" and "down_thresh" parameters
control the transition from the "UP" state to the "DOWN" state while trying to prevent
flappy behavior. Their behavior is best described in terms of an internal failure
counter for a resource which is currently in the "UP" state. The failure counter
starts at zero on state transition into the "UP" state.
Every state poll that results in a failed response, even if other successful responses
are interleaved between them, increments the failure counter. If the failure counter
reaches "down_thresh" the resource is transitioned to the "DOWN" state. However, if
"ok_thresh" successes occur in a row with no failures between them, the failure
counter is reset back to zero.
So with the default values, the expected behavior is that if an "UP" resource
experiences 10 (possibly isolated or intermittent) monitor-polling failures over any
length of time, without a string of 10 successes in a row somewhere within the
sequence to reset the counter, it will transition to the "DOWN" state. Once "DOWN",
it will require 20 successes in a row before transitioning back to the "UP" state.
interval
Integer seconds, default 10, min 1, max 255. Number of seconds between successive
monitoring requests for a given resource.
timeout
Integer seconds, default interval/2, min 1, max 255. Maximum time the monitoring code
will wait for a successful response before giving up and considering the request to be
a failure. Defaults to half of the "interval", and must be less than "interval".
plugin
String, required. This indicates which specific plugin to use to execute the
monitoring requests. Any parameters other than the generic ones listed here are
consumed by the plugin.
There are six monitoring plugins included with gdnsd that can be used in a service_types
definition, each of which may have additional, plugin-specific configuration options in
addition to the generic ones above. Each of these is documented in detail in its own
manpage e.g. "gdnsd-plugin-FOO":
tcp_connect
Checks TCP basic connectivity on a given port. Only supports address resources, not
CNAMEs.
http_status
Checks HTTP connectivity, with options for the port, URL, and vhost to use in the
request, and the acceptable HTTP status codes in the response. Only supports address
resources, not CNAMEs.
extmon
Periodically executes a custom external commandline program to poll for the status of
a resource. Supports both address and CNAME resources.
extfile
Reads the contents of a file on disk to import state monitoring data from another
source. Supports both address and CNAME resources.
static
Configures a static monitoring result, mostly for testing / example code. Supports
both address and CNAME resources.
null
Configures an always-down static result, mostly for testing / example code. Supports
both address and CNAME resources.
PLUGINS
The plugins hash is optional, and contains one key for every dynamic resolution plugin you
wish to load and use. The value must be a hash, and the contents of that hash are
supplied to the plugin to use in configuring itself. If the plugin requires no
configuration, the empty hash "{}" will suffice. It is up to the plugin to determine
whether the supplied hash of configuration data is legal or not.
Monitoring-only plugins can also be given plugin-global level configuration here if the
plugin author deemed it necessary.
gdnsd ships with eight different monitoring plugins, all of which have their own separate
manpage documentation (e.g. "man gdnsd-plugin-FOO"):
reflect
Reflects DNS client source IP and/or edns-client-subnet information back to the
requestor as address data for debugging.
simplefo
Simple primary->secondary failover of monitored addresses
multifo
All-active failover of monitored round-robin address groups
weighted
Weighted-round-robin responses with a variety of behavioral flavors, for both
monitored addresses and CNAMEs.
metafo
Static-ordered address(-group) meta-failover between 'datacenters', which are
resources defined in terms of other plugins. Supports both address and CNAME data.
geoip
Combines metafo's functionality with MaxMind GeoIP databases to select different
datacenter address(-group) preference/failover orderings for different clients based
on approximate geographic location. Supports both address and CNAME data.
null
Returns all-zeros addresses or the CNAME "invalid." - mostly for testing and as simple
example code.
static
Configures static mappings of resources names to IP addresses or CNAMEs - mostly for
testing and as simple example code.
A configuration example showing the trivial plugins, as well as demonstrating the
service_types described earlier:
service_types => {
corpwww_type => {
plugin => http_status
vhost => www.corp.example.com
url_path => /check_me
down_thresh => 5
interval => 5
}
}
plugins => {
null => {},
reflect => {},
static => {
foo = 192.0.2.2
bar = 192.0.2.123
somehost = somehost.example.net.
},
multifo => {
web-lb =>
service_types => [ corpwww_type, xmpp ],
lb01 => 192.0.2.200,
lb02 => 192.0.2.201,
lb03 => 192.0.2.202,
}
}
}
And then in your example.com zonefile, you could have (among your other RRs):
zeros 600 DYNA null
reflect 10 DYNA reflect
reflect-both 10 DYNA reflect!both
pointless 42 DYNA static!foo
acname 400 DYNC static!somehost
www 300/45 DYNA multifo!web-lb
LOW-LEVEL SYNTAX
At the lowest level, the syntax of gdnsd config files roughly resembles an anonymous Perl
data structure (using reference syntax). There are three basic data types for values:
ordered hashes (associative arrays mapping keys to values), ordered arrays of values, and
simple strings. Hashes and arrays can be nested to arbitrary depth. Generally speaking,
whitespace is optional. Single-line comments in both shell ("#") and DNS zonefile styles
(";") are allowed. They run to the end of the current line and are considered to be
whitespace by the parser.
A hash is surrounded by curly braces ("{" and "}"). Keys are separated from their values
by either "=>" or "=" (at your stylistic discretion). Hash keys follow the same rules as
simple string values. Hash values can be simple strings, arrays, or hashes. Key/value
pairs can optionally have a trailing comma for stylistic clarity and separation.
An array is surrounded by square braces ("[" and "]"). Values can be simple strings,
arrays, or hashes. Values can optionally have a trailing comma for style.
Strings (and thus keys) can be written in both quoted and unquoted forms. In the quoted
form, the string is surrounded by double-quotes ("""), and can contain any literal byte
value (even binary/utf-8 stuff, or NUL) other than """ or "\". Those two characters must
be escaped by "\", i.e. "\"" and "\\".
In the unquoted form, there are no surrounding quotes, and the allowed set of unescaped
characters is further restricted. The following are not allowed: "][}{;#,"=\" (that is,
square brackets, curly brackets, semicolons, octothorpes, commas, double quotes, equal
signs, and backslashes). Additionally, the first character cannot be a "$" (dollar sign).
Both forms use the same escaping rules, which are the same RFC-standard escaping rules
used in zone files. The escapes always start with "\". "\" followed by any single byte
other than a digit (0 - 9) is interepreted as that byte. "\" followed by exactly 3 digits
interprets those digits as the unsigned decimal integer value of the desired byte (the 3
digit value cannot exceed 255).
To illustrate the escaping and quoting, the following sets of example strings show
different encodings of the same parsed value:
example
"example"
ex\097mpl\e
"ex\097mpl\e"
internal\"doublequote
"internal\"doublequote"
white\ space
"white space"
"braces{every[where]oh}my"
braces\{every\[where\]oh\}my
"\\==="
"\092==="
"\092\=\=\="
\\\=\=\=
\092\=\=\=
The top level of the config file is an implicit hash with no bracing by default, but can
also be an array bounded by square brackets. This is not legal for the primary gdnsd
configuration file, but could be useful in includefiles (see below).
As a general rule, anywhere the higher-level syntax allows an array of values, you can
substitute a single value. The code will treat it as if it were an array of length 1.
When we refer in other sections above to a value as being an "Integer" (or other specific
scalar type), we're referring to constraints on the content of the character string value.
All scalar values are character strings. "Boolean" values are characters strings which
have the value "true" or "false", in any mix of upper or lower case.
The following 3 example configuration files are identical in their parsed meanings, and
should clarify anything miscommunicated above:
Example 1 (simple and clean):
options = {
listen = [ 192.0.2.1, 192.0.2.2 ],
}
Example 2 (fat arrows, no commas, some arbitrary quoting):
"options" => {
listen => [ 192.0.2.1 192.0.2.2 ]
}
Example 3 (compressed and ugly):
options={listen=[192.0.2.1 192.0.2.2]}
INCLUDING OTHER FILES
vscf now has a mechanism for config includefiles. The syntax is
$include{dir/file} # single file must exist
$include{dir/*} # not ok if no matching files
$include{dir} # ok if no files in dir
where the path can use the same kinds of escaping and/or double-quoting as normal scalar
string data. Whitespace between the path and the surrounding brackets is optional.
Whitespace between $include and the following "{" is not allowed. If the path is relative
(does not begin with /), it is interpreted as relative to the directory containing the
parent file. Includes can nest other includes to arbitrary depth.
The path is normally treated as a glob, allowing the inclusion of multiple files. When
used as a glob, there must be at least one match - it will be an error if there are no
matching files. However, if "path" is not a glob and names an existing directory
explicitly, it will be treated like it was a glob of all files within that directory by
appending "/*", and it will not be an error if there are no files within that directory
(no matches for the glob).
Keep in mind that at the top level of any given vscf file (even include files), the file
must syntactically be either an implicit hash or an explicit, square-bracket-bounded,
array.
The include statement can be used in two distinct contexts within the syntax structure of
a config file:
Value Context
The include statement can replace any whole value (that is, the right hand side of a
hash map entry or a member of an array) with its own contents, which are either a hash
or an array. Note that there is no mechanism for flattening an include-file's array
into the parent array (the whole included array would be a single array item within
the parent array). Also, including multiple files in a single statement (directory
name or glob pattern) are not allowed in value context. Examples:
main config:
options => { listen => $include{foo} }
foo:
[ 127.0.0.1, 127.0.0.2 ]
main config:
plugins => $include{ "bar" }
bar:
geoip => { ... }
extmon => { ... }
Hash-Merge Context
The include statement can also appear in a hash where a key would normally be
expected. In this case, the included file must be in hash (rather than array) form at
the top level, and its contents are merged into the parent hash. The merge is
shallow, and conflicting keys are not allowed. Example:
main config:
options => { ... },
plugins => {
extmon => { ... },
$include{geoip.cfg},
$include{plugins.d},
}
geoip.cfg:
geoip => { ... }
plugins.d/foo:
weighted => { ... }
simplefo => { ... }
plugins.d/bar:
metafo => { ... }
SEE ALSO
gdnsd(8), gdnsd.zonefile(5), gdnsd-plugin-simplefo(8), gdnsd-plugin-multifo(8),
gdnsd-plugin-weighted(8), gdnsd-plugin-metafo(8), gdnsd-plugin-geoip(8),
gdnsd-plugin-extmon(8), gdnsd-plugin-extfile(8)
The gdnsd manual.
COPYRIGHT AND LICENSE
Copyright (c) 2012 Brandon L Black <blblack@gmail.com>
This file is part of gdnsd.
gdnsd is free software: you can redistribute it and/or modify it under the terms of the
GNU General Public License as published by the Free Software Foundation, either version 3
of the License, or (at your option) any later version.
gdnsd is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without
even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with gdnsd. If
not, see <http://www.gnu.org/licenses/>.