A high performance DNS cache designed for Content Delivery Networks, with
built-in security mechanisms to protect origins, clients and itself.
Precompiled binaries (recommended)
- Linux ARM64 (Debian package)
- Linux ARM64 (Universal, glibc)
- Linux ARMv7 (Debian package, gnueabihf)
- Linux ARMv7 (Universal, gnueabihf)
- Linux x86 (Debian package)
- Linux x86 (Universal, glibc)
- Linux x86_64 (Debian package)
- Linux x86_64 (Universal, glibc)
- MacOS x86_64
Installation from source
EdgeDNS requires rust-nightly. Compile and install the server with:
git clone -b 0.3.0 https://github.com/jedisct1/edgedns
cd edgedns
cargo install
Quickstart
- Edit a copy of the
edgedns.toml configuration file
- Run
edgedns -c /path/to/edgedns.toml
On Linux, you may use that
sample systemd service
to start it.
EdgeDNS can protect authoritative servers ("virtual DNS" mode), or act
as a local cache for responses received from a recursive server.
EdgeDNS as a cache for authoritative servers ("virtual DNS" mode)
For this mode, set the type property in the [upstream] section to
authoritative:
[upstream]
# Type of upstream servers: "resolver" or "authoritative"
type = "authoritative"
EdgeDNS will act as a "secondary DNS server" for the zones served by
one or more "primary DNS servers". The external IP address edgedns
is listening to can be configured as a public authoritative server for
the zone.
This will reduce the load on the "primary server", mitigate common
attacks, and ensure a continuity of service even if the primary server
has temporary outages.
Binding as many ports as possible (udp_ports in the [network]
section) is recommended in this mode of operation. This may require
some adjustments to your system configuration. See below.
EdgeDNS as a local DNS cache
For this mode, set the type property in the [upstream] section to
resolver:
[upstream]
# Type of upstream servers: "resolver" or "authoritative"
type = "resolver"
And configure the local host to use 127.0.0.1 as a resolver. EdgeDNS
will cache responses, balance the load across the resolvers set, and
improve your experience by making DNS more reliable.
Operation
EdgeDNS has two modes of operation:
- In "virtual DNS" mode, it acts as an authoritative server, and
sits between authoritative DNS servers and resolvers. It ensures
that only correct queries are sent to upstream servers, balances the
load across multiple upstreams, reduces the load by caching recent and
frequent queries, mitigates DDoS attacks and does its best to respond
to critical queries even when upstream servers are slow or
unresponsive.
- In "resolver" mode, EdgeDNS can act as a simple, non-recursive DNS
cache, sitting between a recursive resolver and stub resolvers.
"virtual DNS" is the default mode, but this can be changed with the
type property in the [upstream] section.
By default, the load is distributed using jump consistent hashing,
ensuring that the upstream servers get a similar share, but queries for
a given zone always favor the same upstream server.
As an alternative, servers can be tried sequentially, and queries are
eventually sent to the first responsive server.
That behavior is controlled by the strategy property in the
[upstream] section. uniform enables consistent hashing, fallback
selects servers in sequence and minload uses the power-of-two-choices
algorithm.
A unique feature of EdgeDNS is that it uses a fixed number of UDP
sockets. Sockets designed to receive responses from upstream servers
are all open at once, and are then kept open forever. Matching
responses with queries is entirely done by the application instead of
the kernel.
As a result, the server will not start if the maximum number of UDP
ports to use is larger than the maximum number of file descriptors
allowed.
Tweaking /etc/security/limits.conf or using ulimit -n might thus
be required prior to starting the server.
By default, only 8 UDP ports are open. This is acceptable for a
local cache ("resolver mode") sending queries to a local resolver on a
trusted network. In all other scenarios, raising this number as much
as possible (up to 64511) using the udp_ports property is highly
recommended.
Live metrics
If the enabled property is set to true in the [webservice]
section, EdgeDNS will serve live metrics that can be collected by the
Prometheus time-series database.
The default URL to access these metrics is http://0.0.0.0:9090/metrics.
Note
This software is still a work in progress. More features are planned,
with a focus on automatic DDoS mitigation.
Features
Reliable
EdgeDNS is written in Rust, which by design prevents common security
and reliability issues while remaining extremely fast.
EdgeDNS can thus be used as a protection layer for DNS resolvers and
authoritative servers.
EdgeDNS has been running flawlessly on the public
scaleway-fr server since January 2016.
DNSSEC support
EdgeDNS is fully compatible with DNSSEC.
Low memory usage
In virtual DNS mode, responses are cached independently instead of
performing zone transfers, in order to favor caching of hot records.
With a large number of zones, and an uneven distribution of queries
across records, this leads to a very low memory usage compared to
secondary servers keeping entire zones.
EDNS0 support
EdgeDNS fully supports EDNS0 both to respond to clients, and to
communicate with upstream servers. This minimizes the number of
queries requiring TCP and reduces latency.
Minimal truncated responses
Responses that don't fit within the maximum payload size supported by
a client get a truncated response, whose content cannot be used by a
resolver or stub resolver.
Instead of forwarding truncated responses sent by authoritative
servers, EdgeDNS directly synthesizes the shortest possible responses.
Correct support for the dns0x20 extension
In order to improve resistance against forgery, some clients support
the dns0x20 extension, which randomizes casing in DNS names. This
shouldn't lead to distinct cache entries. The cache normalize names,
but respect the form initially sent by clients in its responses.
Coalescing of identical queries
Multiple clients can be simultaneously waiting for the same cache
entry to be filled.
Similar in-flight queries are coalesced, and the first received
response is dispatched among all waiting clients.
Latency guarantee
Slow authoritative servers can have a huge impact on clients, even if
this is a temporary situation.
EdgeDNS does its best to guarantee a maximum latency. If a response
that needs to be refreshed doesn't get a response within a given time
frame, EdgeDNS can directly respond with cached records in order to
avoid breaking the latency guarantee.
Short responses to ANY queries
ANY queries are commonly used to conduct DDoS attacks.
The ANY query type has been deprecated for a while, but not answering
queries with the ANY type breaks legacy software, namely Qmail.
Cloudflare handles ANY queries by synthesizing responses with HINFO
records. EdgeDNS implements this proposal as well. It doesn't violate
the protocol, doesn't break Qmail and mitigate abuses, while not
requiring any interactions with authoritative servers.
Query validation
Only valid queries should be sent to authoritative servers. This
mitigates common attacks exploiting vulnerabilities in resolvers
and authoritative servers.
Negative caching
The absence of data is cached. Temporary errors such as SERVFAIL
responses are also cached for a short period of time, in order to
avoid hammering upstream servers.
Automatic failover
Outages of upstream servers are quickly detected, and background
probes are sent to bring them back to the pool as soon as they get
operational again.
Consistent hashing
In order to improve cache locality, the same questions should
preferably be always sent to the same upstream servers.
Consistent hashing limits the amount of reshuffling after servers are
being flagged as down or back up, and is a strategy the proxy can use
in order to distribute queries amount authoritative servers.
As an alternative, EdgeDNS can send data to a primary upstream
servers, and fall back to a list of backup servers in case of an
outage.
Resilience against temporary outages of authoritive servers
If authoritative servers cannot be reached for a given zone, and a
previous version of the response is available, EdgeDNS serves that
version instead of returning a server failure.
If authoritative responses are received, but with a significant delay,
EdgeDNS responds with a previous version of the response, and updates
its cache as soon as the update is effectively being received.
Resilience against cache pollution
An attacker could fill the cache with entries of little relevance, or
invalid entries, in order to reduce the cache efficiency, or partly
disrupt the service.
In order to protect against cache pollution, EdgeDNS uses the
CLOCK-Pro algorithm. This algorithm separately tracks recently used
and frequently used entries.
A significant amount of new entries does not have a perceptible
impact on frequently asked DNS questions.
TCP slots reuse
The number of simultaneous connections coming from the same client IP
address is capped, and dynamically adjusted according to the total
number of free slots.
After the cap is reached, new connections recycle older connections
from the same client IP. A single client opening many TCP connections
doesn't affect the general service availablity.
