tdns

A DNS client command-line tool, with aspirations to become a swiss army knife when it has grown up.

tdns aims to grow into a replacement for the nsupdate and dig commands distributed as part of the ISC bind suite, adding features such as propagation checking for updates and a more convenient (and "standard") command-line interface.

tdns is implemented in Rust, taking advantage of the terrific trust-dns DNS client library, and uses a single-threaded, non-blocking runtime. Translated from developer speak, this means that tdns-udpate should be very light on system resources, and cope well even with unreasonably large tasks, such as monitoring a record in a zone that is served by hundreds of authoritative nameservers.

Note that tdns is currently in its initial development phase. The usual caveats apply. If you're still interested, read on for more information of what is currently working, and what is planned.

Installation

As tdns is written in Rust, you need a Rust toolchain. Rust 1.37 or newer is required. To obtain the latest release from crates.io, use:

cargo install tdns-cli

Alternatively, you can run it directly from the source checkout:

cargo run -- --help

To install from locally checked-out source, use cargo install --path ., which will end up installing the executable in ~/.cargo/bin/tdns, which should already be in your PATH environment variable, if you followed the Rust toolchain installations instructions.

Static build

For deployment to a Linux target, an attractive option is to create a statically linked binary using Rust's MUSL target. This will result in a completely standalone binary, which depends only on the Linux kernel's system call ABI.

# If you haven't installed the MUSL target already, let's do that now:
rustup target add x86_64-unknown-linux-musl
# Build against the MUSL libc target
cargo build --target x86_64-unknown-linux-musl --release
# Let's check it's really a static binary
file target/x86_64-unknown-linux-musl/release/tdns \
  | grep -q 'statically linked' || echo "nope"

Documentation

The documentation for the tdns and its subcommands are provided in the form of Unix man pages, rendered from markdown source files, which can be turned in to troff format for viewing with the man command using pandoc. Note that to the markdown sources are tailored toward producing good output when fed through pandoc, and will not be rendered that nicely on github or alike, and is not ideal to read in plain, either.

You can generate the manpages using the included Makefile, and view the man page using the Unix man command:

make man
man -l tdns.1
man -l tnds-query.1
man -l tnds-update.1

HTML renderings of the manpages are also created when running make, these are also available online:

• tdns.1, providing an overview.
• tdns-query.1, documenting the tdns query subcommand.
• tdns-update.1, documenting the tdns update subcommand.

Available subcommands

tdns query

This subcommand can be used as a partial substitute for dig +short; extending the functionality is planned.

tdns update

A dynamic DNS updater and update checker, using the mechanism described in RFC 2136.

tdns update updates and/or monitors an entry in a DNS zone. The updating functionality is currently a limited subset of what the nsupdate utility from the ISC BIND provides, but providing both updates and monitoring in a single native executable is novel, at least to the author's knowledge. There are doubtlessly numerous shell scripts around that provide similar functionality, with varying degrees of sophistication. tdns update aims to its job correctly and efficiently, taking no shortcuts.

With a single tnds update invocation, you can both perform a DNS update operation, and wait for all the authoritative nameservers in the zone to provide the updated records.

Missing features

Without those, tdns update cannot function reliably, or can be considered not doing the job properly:

• If no --resolver option is provided, make use of all the resolvers specified in /etc/resolv.conf, not just the first one.
• Probe all addresses an NS entry resolves to.
• IPv6 support; the code is largely agnostic of IP address family, but IPv6 support has not yet been actively worked on.

Planned features

• To become a full replacement for nsupdate, a more elaborate way for describing the update, similar to the nsupdate "scripts" is needed; adapting the command-line interface is not suitable for more complex update operations.
• Once a mechanism for describing an update in some kind of DSL is added, it should be quite easy to allow updating multiple zones concurrently in a single run. This functionality is probably not that useful in practice, but who knows...
• Increase the test coverage of the test suite; the infrastructure and some basic tests are present, but coverage is quite limited currently.

Example use case

This is the scenario which prompted the development of tdns update.

When obtaining TLS certificates from letsencrypt using the DNS-01 protocol, it is necessary to ensure that letsencrypt is only told to verify the challenge after it can be reliably retrieved. With secondary DNS servers, it can take a while until the update is completely rolled out to all of them. tdns update can be used as part of the hook script to deploy the letsencrypt challenge to DNS.

License

Copyright © 2019 Andreas Rottmann

This program 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.

This program 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 this program; if not, see https://www.gnu.org/licenses.

Additional permission under GNU GPL version 3 section 7

If you modify this Program, or any covered work, by linking or combining it with OpenSSL (or a modified version of that library), containing parts covered by the terms of OpenSSL License, the licensors of this Program grant you additional permission to convey the resulting work. Corresponding Source for a non-source form of such a combination shall include the source code for the parts of OpenSSL used as well as that of the covered work.

Contributions

Unless explicitly indicated otherwise, any contribution intentionally submitted for inclusion in this crate:

• Will be licensed under the GNU GPL version 3.0, or later, with the additional permissions listed above.
• The contributor additionally grants the crate maintainer the right to re-license parts or all of the crate's code, including the contribution, to the dual MIT/Apache-2.0 license. This is provision is for the case that some part of the crate's code turns out to be of general utility, such that it would benefit from being split out and being given a more liberal, non-copyleft license.