How to use a TLS proxy with a DNS nameserver
It is of course possible to configure a TLS proxy in front of a DNS nameserver to provide DNS-over-TLS. Example configurations for nginx and haproxy are given here.
A more comprehensive setup guide using Docker has been provided by Warren Kumari: dprive-nginx-bind (Thanks Warren!)
One of the limitations of using a proxy is that without additional work this will normally mean that the client address is not visible to the nameserver, which can cause issues with NAT64, RRL, RPZ etc. There are ways round this using address re-write rules but we don't detail that here. In future a solution like https://datatracker.ietf.org/doc/draft-bellis-dnsop-xpf/ might become standard.
To use the following with BIND to offer a TLS service, configure BIND based on the following named.conf snippet
- This assumes BIND 9.12 which supports response padding (comment that line out if you are using an earlier version)
- The rncd and logging config is used to capture traffic volume stats - statistics can be dumped periodically with the 'rndc stats' command
For all but lightly loaded systems, you will need to tune the number of processes or threads available to HAProxy. Unlike the nginx configuration above, which specifies an automatic configuration of the number of worker processes, HAProxy needs to have these quantities set by hand. The simplest way is to set configuration item
nbproc to an appropriate number; we suggest the number of threads or processes used by the nameserver. For more advanced tuning options, including setting CPU affinity, see the HAProxy documentation or this blog post.
If you use HAProxy and have generated your certificates from Let's Encrypt then you need to combine the certificate chain and key into one file using a command similar to: