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+.. highlight:: none
+.. _Requirements:
+
+************
+Requirements
+************
+
+Hardware
+========
+
+Knot DNS requirements are not very demanding for typical
+installations, and a commodity server or a virtual solution will be
+sufficient in most cases.
+
+However, please note that there are some scenarios that will require
+administrator's attention and some testing of exact requirements before
+deploying Knot DNS to a production environment. These cases include
+deployment for a large number of zones (DNS hosting), large number
+of records in one or more zones (TLD), or large number of requests.
+
+CPU requirements
+----------------
+
+The server scales with processing power and also with the number of
+available cores/CPUs. Enabling Hyper-threading is convenient if supported.
+
+There is no lower bound on the CPU requirements, but it should support
+memory barriers and atomic instructions (i586 and newer).
+
+Network card
+------------
+
+The best results have been achieved with multi-queue network cards. The
+number of multi-queues should equal the total number of CPU cores (with
+Hyper-threading enabled).
+
+Memory requirements
+-------------------
+
+The server implementation focuses on performance and thus can be quite
+memory demanding. The rough estimate for memory requirements is
+3 times the size of the zone in the plain-text format. Again this is only
+an estimate and you are advised to do your own measurements before
+deploying Knot DNS to production.
+
+.. NOTE::
+   To ensure uninterrupted serving of the zone, Knot DNS
+   employs the Read-Copy-Update mechanism instead of locking and thus
+   requires twice the amount of memory for the duration of incoming
+   transfers.
+
+Operating system
+================
+
+Knot DNS itself is written in a portable way and can be compiled
+and run on most UNIX-like systems, such as Linux, \*BSD, and macOS.
+
+Required libraries
+==================
+
+Knot DNS requires a few libraries to be available:
+
+* libedit
+* gnutls >= 3.3
+* liburcu >= 0.5.4
+* lmdb >= 0.9.15
+
+.. NOTE::
+   The LMDB library is included with Knot DNS source code. However, linking
+   with the system library is preferred.
+
+Optional libraries
+==================
+
+International Domain Names support (IDNA2008 or IDNA2003) in :doc:`kdig<man_kdig>`:
+
+* libidn2 (or libidn)
+
+Systemd's startup notification mechanism and journald logging:
+
+* libsystemd
+
+Dnstap support in :doc:`kdig<man_kdig>` or module :ref:`dnstap<mod-dnstap>`:
+
+* fstrm (and protobuf-c if building from source code)
+
+Linux :manpage:`capabilities(7)` support, which allows the server to be started
+as a non-root user/group, binding to privileged ports (53), and giving up all
+its capabilities, resulting in a completely unprivileged process:
+
+* libcap-ng >= 0.6.4
+
+MaxMind database for **geodb** support in module :ref:`geoip<mod-geoip>`:
+
+* libmaxminddb0
+
+DNS-over-HTTPS (DoH) support in :doc:`kdig<man_kdig>`:
+
+* libnghttp2
+
+The :ref:`XDP functionality <Mode XDP>` and :doc:`kxdpgun <man_kxdpgun>`
+tool. These are only supported on Linux operating systems. See the chapter
+:ref:`Mode XDP <Mode XDP_pre-requisites>` for software and hardware
+recommendations.
+
+* libbpf
+* libxdp (if libbpf >= 1.0)
+* libmnl (for kxdpgun)
+
+DNS-over-QUIC (DoQ) support in :doc:`knotd<man_knotd>`, :doc:`kxdpgun<man_kxdpgun>`,
+and :doc:`kdig<man_kdig>`:
+
+* libngtcp2 >= 0.17.0 (or embedded one via `--enable-quic`)
+* gnutls >= 3.7.3
+* :ref:`Mode XDP` (for knotd and kxdpgun)