Domain Name System Operations A. Gavrichenkov
Internet-Draft Qrator Labs
Intended status: Standards Track March 05, 2018
Expires: September 6, 2018
Domain Name System Service Application Programming Interface
draft-gavrichenkov-dnsop-dnssapi-00
Abstract
Managed DNS services are widely used to maintain DNS zones.
Virtually all of them have an API of some sort, in most cases an XML-
RPC or JSON-RPC API, while most of them lack the support of zone
transfers. The latter is unlikely to change any time soon due to the
reasons outlined below. This document describes a protocol, a common
denominator of existing API protocols, that both a service provider
and its customer can use to exchange information about DNS zones and
policies.
Status of This Memo
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This Internet-Draft will expire on September 6, 2018.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Functionality supported by managed DNS service providers . . 3
2.1. Failover . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Location-based DNS routing . . . . . . . . . . . . . . . 4
2.3. Firewalling . . . . . . . . . . . . . . . . . . . . . . . 4
2.4. Load balancing . . . . . . . . . . . . . . . . . . . . . 4
2.5. Rate limiting . . . . . . . . . . . . . . . . . . . . . . 5
2.6. Statistics . . . . . . . . . . . . . . . . . . . . . . . 5
3. General policy on additional extensions . . . . . . . . . . . 5
4. DNSSAPI protocol specification . . . . . . . . . . . . . . . 5
5. Normative References . . . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
Today, managed DNS services are a common solution for setting up and
maintaining a DNS infrastructure for an enterprise. Those services
often offer convenient functionality out of the box, e.g. failover,
granular load balancing or geotargeting, while being more resilient
to distributed denial-of-service attacks than a simple in-house
solution could be.
However, the main challenge with managed DNS services is managing
them. In case there's an update in the DNS setup, an enterprise
would want it to be propagated to the managed service as soon as
possible. However, existing mechanisms like zone transfer [RFC5936]
or dynamic updates [RFC2136] are rarely implemented by managed DNS
service providers, leaving an enterprise with an uncomfortable choice
of either using a Web interface to manually set up zones and
policies, or using an API of that provider.
There are reasons why existing mechanisms fail to gain popularity
among service providers and their customers. First, zone transfer
doesn't support virtually any of the features a customer might want
from a service provider, except for a trivial name resolution. For
instance, it is impossible to propagate a geography-based policy
towards a service provider using zone transfer itself, with
accordance to standard; this can be achieved ad hoc if both a
customer and a provider agree on a particular zone naming policy,
however, as this is not supported by an Internet standard, it makes
changing a service provider or adding a new one a touch challenge.
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Second, an enterprise which is using a managed DNS service might not
be operating its own primary DNS server at all, sticking with simple
deployment database exports. An XML-RPC or JSON-RPC API fits that
model rather well, as handlers for those are highly likely to be
implemented by a personnel quite familiar with the concepts of XML
and/or JSON-RPC. However, implementing a binary protocol might be
viewed as another challenge.
Next, both zone transfers and dynamic updates go in one direction,
while an enterprise generally might want a feedback, including, but
not limited to, traffic statistics overview, average response time,
query type statistics, and so on. This is, once again, usually
incorporated in a managed DNS service API.
However, the main issue with the latter is that there's currently no
Internet standard providing a guidance for the API design. As the
result, each DNS provider implements and maintains its own API, with
its own naming schemes and type layouts, once again making migration
from one provider to another - or operating more than one provider
simultaneously - a challenge for network and system operations
departments.
This might be viewed by some as a sort of a vendor lock-in, however,
this issue alone is highly unlikely to really help retaining a
customer who is somehow dissatisfied with the service and is eager to
change the provider. What is beyond doubt is that a customer will
just be further disappointed after they will face all the projected
issues while moving to another service.
This way, it might be useful to agree on a common API protocol, JSON-
RPC-based, with a built-in support for all the features offered by
managed DNS services today, and extensible in order to add more
features in future. The purpose of this document is to provide a
description of such a protocol. This protocol might then be viewed
as a guidance for new DNS providers which are going to implement
their API, or for existing providers refactoring their code.
2. Functionality supported by managed DNS service providers
Here is the list of features implemented by managed DNS service
providers (MDNSSP) today.
2.1. Failover
Enterprises are often in a high demand for online business
continuency, and as the result, they opt for some redundancy. E.g.
if they operate a Web site, they often have more than one server, on
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more than one IP address, serving the Web content. There are mainly
two options to implement that redundancy:
o Those servers may be put in an anycast IP prefix, announced from
different locations, so that if a location goes down, its traffic
is then served by nearest network locations
o Those servers may operate simultaneously, on a round-robin basis,
all being put in a DNS A record entry.
The issue with the latter approach is that one has to set up
monitoring and keep-alive checks of some sort to take a failing
server out of round-robin as soon as possible. MDNSSP often offer
convenient built-in features to do that.
2.2. Location-based DNS routing
Geography-based DNS routing, known also as geo-balancing, is a widely
used method to reduce the latency between network clients and
services by looking at the IP source of a DNS query and returning an
answer with an IP address which is as close to a client as possible
in terms of geolocation. The distance between a client and each in
the set of servers may be measured in different ways, including
looking at the country a source IP address belongs to, a region or
city, or even comparing latitude and longitude.
However, due to routing policies of network operators and also due to
the reported inaccuracy of regional internet registries' databases
(which are the only officially recognized source of the mapping
between IP addresses and countries and geographic regions), there
might be latency issues now with geography-based DNS routing. Some
MDNSSP handle that by allowing more specific policies to be set up,
e.g. ASN-based or prefix-based policies.
2.3. Firewalling
Firewall access rules might be viewed as a subset of location-based
policies, except for a simpler policy of just dropping the traffic
instead of processing it. However, sometimes further requirements
may take place, e.g. forcing a challenge towards a source IP address,
and so on. Those features are a subject of a different extension
than location-based routing, being applied before it.
2.4. Load balancing
There are a lot of things a DNS server can do to balance traffic
towards a set of servers. The simplest example would be shuffling
answers based on their weight.
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2.5. Rate limiting
An MDNSSP may limit the amount of requests coming towards a single
server by returning intentionally wrong reponse to an A query, e.g.
NXDOMAIN. This might help to keep a server running in case of a
sudden traffic spike.
The exact amount of queries triggering that condition must be
specified as an argument during the setup.
2.6. Statistics
Generally, an MDNSSP offers metrics regarding the overall inbound and
outbound network traffic, query count, average and/or median response
time, and all or some of this data for different query names, types,
response codes and so on.
3. General policy on additional extensions
The API is designed to be extensible. An MDNSSP SHOULD implement
functionality in a way specified by this document in case this
functionality can be handled by methods described in this
specification. However, an MDNSSP MAY implement its own private
extension if the standard functionality doesn't fit their needs.
An extension for the DNSSAPI protocol must either follow the naming
structure for the private extensions' domain or use an IANA-allocated
extension name.
4. DNSSAPI protocol specification
...
5. Normative References
[RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound,
"Dynamic Updates in the Domain Name System (DNS UPDATE)",
RFC 2136, DOI 10.17487/RFC2136, April 1997,
<https://www.rfc-editor.org/info/rfc2136>.
[RFC5936] Lewis, E. and A. Hoenes, Ed., "DNS Zone Transfer Protocol
(AXFR)", RFC 5936, DOI 10.17487/RFC5936, June 2010,
<https://www.rfc-editor.org/info/rfc5936>.
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Author's Address
Artyom Gavrichenkov
Qrator Labs
Email: ag@qrator.net
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