confluent2dnsmasq(8) -- Generate dnsmasq static DHCP reservations for nodes
===============================================================================

## SYNOPSIS

`confluent2dnsmasq [options] <noderange>`  
`confluent2dnsmasq <noderange>`  
`confluent2dnsmasq --all-options <noderange>`  
`confluent2dnsmasq -n <noderange>`  

## DESCRIPTION

`confluent2dnsmasq` generates a dnsmasq configuration fragment of static
DHCP reservations for a noderange, using the confluent database as the source
of truth.  Each `net.<network>.<attribute>` group is pulled together and one
`dhcp-host=` reservation is emitted for **every network that has a hardware
address** (`net.hwaddr`, `net.bmc.hwaddr`, `net.eth.mynetwork.hwaddr`, and so
on; the network component may itself contain several dotted parts).  Networks
without a `hwaddr` (for example InfiniBand interfaces identified only by a
GUID) are skipped.

For each reservation, `net.<network>.ipv4_address` supplies the reserved
address.  The `/prefixlen` suffix on that address is used to compute the
enclosing subnet; if the address carries no `/prefixlen`, the prefix length is
filled in from the matching directly-attached route in the host's routing
table.  One `dhcp-range=<network>,static,<netmask>,<lease>` line is emitted per
distinct subnet.  dnsmasq will not answer DHCP requests on a subnet that has no
covering `dhcp-range`, even when every address on it is statically reserved, so
these ranges are emitted by default (see `--no-range`).  An address that has
neither an explicit prefix nor a matching local route still yields a
`dhcp-host` reservation, but no subnet or `dhcp-range` is derived for it and a
warning is printed.

The reservation name is the first token of `net.<network>.hostname`, falling
back to the node name itself for the primary (unnamed) network, and omitted for
a named network that has no hostname.  Only IPv4 node addresses are used for
reservations and ranges.

By default the fragment begins with a `bind-dynamic` directive so that dnsmasq
can bind DHCP to networks confluent is using, too (see `--no-bind-dynamic`).

Also by default, a `listen-address` line is emitted for `127.0.0.1`, for
`::1`, and for this host's own address on each managed subnet (see 
`--no-listen-address`).  The per-subnet addresses are read from the routing
table of the host the command runs on, so run it on the dnsmasq host; only
subnets the host is directly attached to are added.  Besides telling dnsmasq
where to listen, the presence of any `listen-address` line disables the default
`local-service` (or `local-service=host`) restriction in `dnsmasq.conf` that
would otherwise limit dnsmasq to localhost.

Additional data can optionally be added to the DHCP reply from the confluent
database (see OPTIONS; all are off by default).  Each such option is scoped to
the subnet it belongs to using a dnsmasq tag: the `dhcp-host` lines for that
subnet are given a `set:<tag>` and the corresponding `dhcp-option` lines a
matching `tag:<tag>`.  Values are aggregated per subnet; if two nodes on the
same subnet disagree (for example two different gateways), a warning is printed
and the first value is used.

The configuration is written to `/etc/dnsmasq.d/confluent-dhcp.conf` (override
with `--target`) and regenerated on each run, replacing the file atomically.
If the existing file was generated with different content-affecting arguments
(the preview and confirmation flags `-n` and `-y` are ignored for this
comparison), you are asked to confirm before it is overwritten; the prompt is
skipped with `-y` and is refused when there is no controlling terminal.  If a
run produces no reservations at all (for example an empty noderange or a failed
read), `confluent2dnsmasq` refuses to overwrite the existing file unless
`--allow-empty` is given.

## OPTIONS

* `--target PATH`:
  Path of the configuration file to write.  Defaults to
  `/etc/dnsmasq.d/confluent-dhcp.conf`.

* `--tag-prefix PREFIX`:
  Prefix used when generating dnsmasq tag names for per-subnet options.
  Defaults to `cdhcp`, yielding tags such as `cdhcp_10_28_104_0_21`.

* `--no-bind-dynamic`:
  Do not emit the `bind-dynamic` line.  It is emitted by default. Note that
  `bind-dynamic` is a global dnsmasq directive and must not be combined with
  a `bind-interfaces` directive set elsewhere. Without it, dnsmasq may conflict
  with confluent's own DHCP unless `bind-dynamic` is set elsewhere in the
  dnsmasq configuration; a warning is printed.

* `--no-listen-address`:
  Do not autodetect or emit `listen-address` lines.  By default a
  `listen-address` line is emitted for `127.0.0.1`, for `::1`, and for this
  host's address on each managed subnet.  With this flag you must set
  `interface`, `except-interface`, or `listen-address` yourself (or disable
  `local-service`/`local-service=host` in `dnsmasq.conf`) for dnsmasq to serve
  the cluster networks alongside confluent; a warning is printed as a reminder.

* `--no-range`:
  Do not emit `dhcp-range` lines, leaving range and subnet declarations to be
  managed elsewhere.  Remember that dnsmasq will not serve DHCP on a subnet
  that has no covering `dhcp-range`.  Per-subnet options are still scoped via
  host tags, so they keep working with a range you declare yourself.

* `--lease TIME`:
  Lease time applied to the emitted `dhcp-range` lines.  Defaults to `24h`.
  Accepts any dnsmasq lease syntax (for example `1h`, `24h`, `infinite`).
  Pass an empty string to omit the lease field entirely.

* `-n`, `--stdout`:
  Write the configuration to standard output instead of the target file, which
  is left untouched.  Useful for previewing.

* `-y`, `--yes`:
  Do not prompt for confirmation when the existing configuration was generated
  with different settings; regenerate anyway.  Without it a settings change is
  confirmed interactively, and refused when there is no controlling terminal.

* `--allow-empty`:
  Write the file even when no reservations were produced.  By default an empty
  result does not overwrite the existing file, to avoid discarding a good
  configuration after an empty or failed read.

* `--all-options`:
  Enable all of the optional reply-data options below at once.

* `--gateway`, `--router`:
  Add a router (DHCP option 3) per subnet, taken from
  `net.<network>.ipv4_gateway`.

* `--dns`:
  Add DNS servers (DHCP option 6) per subnet, taken from `dns.servers`.

* `--domain`:
  Add a domain name (DHCP option 15) per subnet, taken from `dns.domain`.

* `--ntp`:
  Add NTP servers (DHCP option 42) per subnet, taken from `ntp.servers`.

* `--mtu`:
  Add an interface MTU (DHCP option 26) per subnet, taken from
  `net.<network>.mtu`.

* `-h`, `--help`:
  Show a help message and exit.

## EXAMPLES

* Generate reservations for a noderange and write the default file:
  `# confluent2dnsmasq everything`  

* Preview the configuration for one node without writing anything:
  `# confluent2dnsmasq -n node01`  

* Include all optional reply data (gateway, DNS, domain, NTP, MTU):
  `# confluent2dnsmasq --all-options everything`  

* Include only the gateway, and use an eight hour lease:
  `# confluent2dnsmasq --gateway --lease 8h everything`  

* Regenerate non-interactively (for example from cron) after changing options, without the confirmation prompt:
  `# confluent2dnsmasq --all-options -y everything`  

* Emit only reservations (no ranges) to a custom file kept beside your own range and listen interface definitions:
  `# confluent2dnsmasq --no-listen-address --no-range --target /etc/dnsmasq.d/confluent-reservations.conf everything`  

## GENERATED CONFIGURATION

Given the following confluent attributes for node `node01`:

    node01: net.hwaddr: 10:ff:e0:af:af:f5
    node01: net.ipv4_address: 10.28.90.1/21
    node01: net.ipv4_gateway: 10.28.88.1
    node01: net.bmc.hwaddr: 10:ff:e0:a4:cf:b6
    node01: net.bmc.hostname: node01-bmc
    node01: net.bmc.ipv4_address: 10.28.106.1/21
    node01: net.bmc.ipv4_gateway: 10.28.104.1
    node01: net.ib0.hostname: node01-ib0
    node01: net.ib0.ipv4_address: 10.28.101.1/21

`confluent2dnsmasq node01`, run on a dnsmasq host whose own addresses on the
two managed subnets are `10.28.88.250` and `10.28.104.250`, writes the file
below.  The `ib0` network is skipped because it has no `hwaddr`; the two
remaining networks each yield a subnet (with its `dhcp-range`) and a
reservation, and a `listen-address` line is emitted for localhost and for this
host's address on each subnet:

    # Managed by confluent2dnsmasq -- DO NOT EDIT BY HAND.
    # Regenerate: confluent2dnsmasq node01
    # Generated 2026-06-28 12:00:00 +0000

    # Allow confluent and dnsmasq to share the same network for DHCP
    bind-dynamic

    # Listen on localhost plus this host's address on each managed subnet,
    # so dnsmasq serves these networks alongside confluent and bind-dynamic
    # (a listen-address line also overrides local-service in dnsmasq.conf).
    listen-address=127.0.0.1
    listen-address=::1
    listen-address=10.28.88.250
    listen-address=10.28.104.250

    # subnet 10.28.88.0/21
    dhcp-range=10.28.88.0,static,255.255.248.0,24h
    dhcp-host=10:ff:e0:af:af:f5,10.28.90.1,node01

    # subnet 10.28.104.0/21
    dhcp-range=10.28.104.0,static,255.255.248.0,24h
    dhcp-host=10:ff:e0:a4:cf:b6,10.28.106.1,node01-bmc

Adding `--gateway` scopes a router option to each subnet through a tag, and the
matching `dhcp-host` lines gain a `set:` tag so the option reaches them:

    # subnet 10.28.88.0/21
    dhcp-range=10.28.88.0,static,255.255.248.0,24h
    dhcp-option=tag:cdhcp_10_28_88_0_21,option:router,10.28.88.1
    dhcp-host=10:ff:e0:af:af:f5,set:cdhcp_10_28_88_0_21,10.28.90.1,node01

    # subnet 10.28.104.0/21
    dhcp-range=10.28.104.0,static,255.255.248.0,24h
    dhcp-option=tag:cdhcp_10_28_104_0_21,option:router,10.28.104.1
    dhcp-host=10:ff:e0:a4:cf:b6,set:cdhcp_10_28_104_0_21,10.28.106.1,node01-bmc

## NOTES

`bind-dynamic` is a global dnsmasq option; if it is set here it must not be
contradicted by a `bind-interfaces` directive elsewhere in the configuration.

The autodetected `listen-address` lines double as the mechanism that relaxes
dnsmasq's default `local-service`/`local-service=host` restriction (any
`interface`, `except-interface`, or `listen-address` line does), which is what
lets dnsmasq answer on the cluster networks instead of only localhost.
Detection only covers subnets the host running the command is directly attached
to, so run it there; with `--no-listen-address` you must supply `interface`,
`except-interface`, or `listen-address` yourself, or disable `local-service`.

After (re)generating the file, validate it with `dnsmasq --test` and restart
dnsmasq (for example `systemctl restart dnsmasq`); a reload (SIGHUP) does not
re-read `listen-address` or interface bindings.

## FILES

* `/etc/dnsmasq.d/confluent-dhcp.conf`:
  Default output file (override with `--target`).

## SEE ALSO

nodeattrib(8), noderange(5), dnsmasq(8)
