dnsdist 1.3.0 released

We are very happy to announce the 1.3.0 release of dnsdist, with a huge emphasis on privacy and scalability.

Privacy

A lot of users were interested in DNS over TLS support in dnsdist, to protect the privacy and integrity of queries and responses in transit between the client and dnsdist. We have been supporting DNSCrypt since 1.0.0, and improved it in this release by adding support for multiple active certificates and the new xchacha20 algorithm, but DNS over TLS is getting more traction and it made complete sense to support it as well in dnsdist. Our implementation can use either OpenSSL or GnuTLS, and we advise to enable both backends during compilation in order to be able to quickly switch from one to another should a serious vulnerability in one of them be found.

Scalability

As dnsdist is deployed on huge setups, we noticed that it did not scale as well as we expected over a large number of CPU cores. We investigated and found several points of contention, which we addressed by going lock-less whenever possible, and by reducing the granularity of the involved locks when it was not. This led to the optional sharding of the packet cache and our in-memory ring buffers, as well as a new per-pool mutex replacing the global Lua one for non-Lua load-balancing policies.

We had known for a while that dnsdist opening a single socket towards each backend was not performing too well in some scenarios, for example in front of a PowerDNS Recursor with multiple threads, reuseport support enabled and pdns-distribute-queries set to no, because the kernel would then not distribute queries evenly over the different threads. A known work-around was to add the same backend several times in the configuration, but it made metrics hard to understand and caused an unnecessary amount of contexts switching. Starting with 1.3.0, dnsdist supports opening a configurable amount of sockets towards a single backend.

Finally we observed that CPU pinning made a huge difference on some setups, especially on NUMA architecture, so we added the possibility to pin client and backend facing threads to specific CPU cores.

XPF

The solution to pass the client IP on to the backend in dnsdist has always been to add an EDNS Client Subnet option to the query. While it does work nicely, ECS was not designed for this use case and thus lacks some relevant information like the original source and destination ports, as well as the original destination IP. It also makes it impossible to keep any existing ECS information and forward the original source IP.
In coordination with the nice people from ISC, PowerDNS is working on a new solution called XPF, whose current draft is now implemented in dnsdist.

dnstap

In addition to our existing protocol buffer-based solution to export live information on queries and responses processed by dnsdist, Justin Valentini and Chris Hofstaedtler contributed support for exporting queries and responses over the dnstap protocol, which is supported by several other open source DNS servers and can be processed by third party tools.

Older versions

With the release of 1.3.0 today, we are also announcing that the 1.0 and 1.1 branches of dnsdist are now end of life and will not receive any updates, not even security fixes.
Note: Users with a commercial agreement with PowerDNS.COM BV or Open-Xchange can receive extended support for releases which are End Of Life. If you are such a user, these EOL statements do not apply to you.

Other Changes

As a final note, please be aware of three noteworthy changes in this new version:

  • First we removed the –daemon option, in which we kept finding new bugs. Very few users were actually using it, and since most OS provide at least one supervisor we decided to simply remove it ;
  •  Secondly we added the possibility to restrict access to the console using an ACL when it’s bound to a non-loopback IP. The default ACL allows connections from 127.0.0.1 and ::1 only, so you might need to update it to keep using the console over the network. Please make sure that you have enabled encryption before doing so ;
  • We finally removed some functions that were deprecated in 1.2.0 because they were redundant and made it harder to understand how the rules and actions actually work. Please have a look at the documentation to update your configuration.

Please see the dnsdist website for the more complete changelog and the current documentation.

Release tarballs are available on the downloads website.

Several packages are also available on our repository.

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