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Network Working Group E. Wilde
Internet-Draft CA Technologies
Intended status: Standards Track November 12, 2017
Expires: May 16, 2018
The Sunset HTTP Header
draft-wilde-sunset-header-04
Abstract
This specification defines the Sunset HTTP response header field,
which indicates that a URI is likely to become unresponsive at a
specified point in the future. It also defines a sunset link
relation type that allows linking to resources providing information
about an upcoming resource or service sunset.
Note to Readers
This draft should be discussed on the ART mailing list
(<https://www.ietf.org/mailman/listinfo/art>).
Online access to all versions and files is available on GitHub
(<https://github.com/dret/I-D/tree/master/sunset-header>).
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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and may be updated, replaced, or obsoleted by other documents at any
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This Internet-Draft will expire on May 16, 2018.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Temporary Resources . . . . . . . . . . . . . . . . . . . 3
1.2. Migration . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3. Retention . . . . . . . . . . . . . . . . . . . . . . . . 3
1.4. Deprecation . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. The Sunset HTTP Response Header . . . . . . . . . . . . . . . 4
4. Sunset and Caching . . . . . . . . . . . . . . . . . . . . . 4
5. The Sunset Link Relation Type . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6.1. The Sunset Response Header . . . . . . . . . . . . . . . 6
6.2. The Sunset Link Relation Type . . . . . . . . . . . . . . 6
7. Implementation Status . . . . . . . . . . . . . . . . . . . . 6
8. Security Considerations . . . . . . . . . . . . . . . . . . . 7
9. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
10.1. Normative References . . . . . . . . . . . . . . . . . . 8
10.2. Informative References . . . . . . . . . . . . . . . . . 9
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
As a general rule, URIs should be stable and persistent, so that
applications can use them as stable and persistent identifiers for
resources. However, there are many scenarios where for a variety of
reasons, URIs have a limited lifetime. In some of these scenarios,
this limited lifetime is known in advance. In this case, it can be
useful for clients if resources make this information about their
limited lifetime known. This specification defines the Sunset HTTP
response header field, which indicates that a URI is likely to become
unresponsive at a specified point in the future.
This specification also defines a link relation type "sunset" that
allows to provide information about a resource's or a service's
sunset policy, and/or upcoming sunsets, and/or possible mitigation
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scenarios for resource/service users. This specification does not
place any constraints on the nature of the linked resource, which can
be targeted at humans, at machines, or a combination of both.
Possible scenarios for known lifetimes of resources include, but are
not limited to the following scenarios.
1.1. Temporary Resources
Some resources may have a limited lifetime by definition. For
example, a pending order represented by a resource may already list
all the details of the order, but may only exist for a limited time
unless it is confirmed and only then becomes permanent. In such a
case, the service managing the pending order can make this limited
lifetime explicit, allowing clients to understand that the pending
order, unless confirmed, will disappear at some point in time.
1.2. Migration
If resources are changing identity because a service migrates them,
then this may be known in advance. While it may not yet be
appropriate to use HTTP redirect status codes (3xx), it may be
interesting for clients to learn about the service's plan to take
down the original resource.
1.3. Retention
There are many cases where regulation or legislation require that
resources are kept available for a certain amount of time. However,
in many cases there also is a requirement for those resources to be
permanently deleted after some period of time. Since the deletion of
the resource in this scenario is governed by well-defined rules, it
could be made explicit for clients interacting with the resource.
1.4. Deprecation
For Web APIs one standard scenario is that an API or specific subsets
of an API may get deprecated. If this is planned in advance, then
for the time before the actual deprecation is rolled out, the
resources that will be affected by the deprecation can make the date
of their deprecation known. This allows consumers of the API to be
notified of the upcoming deprecation.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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3. The Sunset HTTP Response Header
The Sunset HTTP response header field allows a server to communicate
the fact that a resource is expected to become unresponsive at a
specific point in time. It provides information for clients which
they can use to control their usage of the resource.
The Sunset header contains a single timestamp which advertises the
point in time when the resource is expected to become unresponsive.
The Sunset value is an HTTP-date timestamp, as defined in
Section 7.1.1.1 of [RFC7231], and SHOULD be a timestamp in the
future.
Timestamps in the past SHOULD be considered to mean the present time,
meaning that the resource is expected to become unavailable at any
point in time.
Sunset = HTTP-date
For example
Sunset: Sat, 31 Dec 2018 23:59:59 GMT
Clients SHOULD treat Sunset timestamps as hints: It is not guaranteed
that the resource will in fact be available until that time, and will
not be available after that time. However, since this information is
provided by the resource itself, it does have some credibility.
After the Sunset time has arrived, it is likely that interactions
with the resource will result in client-side errors (HTTP 4xx status
codes), redirect responses (HTTP 3xx status codes), or the client
might not be able to interact with the resource at all. The Sunset
header does not expose any information about which of those behaviors
can be expected.
Clients not interpreting an existing Sunset header field can operate
as usual and simply may experience the resource becoming unavailable
without getting any notification about it beforehand.
4. Sunset and Caching
It should be noted that the Sunset HTTP response header field serves
a different purpose than HTTP caching [RFC7234]. HTTP caching is
concerned with making resource representations (i.e., represented
resource state) reusable, so that they can be more efficiently used.
This is achieved by using header fields that allow clients and
intermediaries to better understand when a resource representation
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can be reused, or when resource state (and thus the representation)
may have changed.
The Sunset header field is not concerned with resource state at all.
It only signals that a resource is expected to become unavailable at
a specific point in time. There are no assumptions about if, when,
or how often a resource may change state in the meantime.
For these reasons, the Sunset header field and HTTP caching should be
seen as complementary, and not as overlapping in scope and
functionality.
5. The Sunset Link Relation Type
The Sunset HTTP header field indicates the upcoming retirement of a
resource or a service. In addition, resource may want to make
information available that provides additional information about how
retirement will be handled for resources or services. This
information can be broadly described by the following three topics:
Sunset policy: The policy for which resources and in which way
sunsets may occur may be published as part of service's
description. Sunsets may only/mostly affect a subset of a
service's resources, and may be exposed according to a certain
policy (e.g., one week in advance).
Upcoming sunset: There may be additional information about an
upcoming sunset, which can be published as a resource that can be
consumed by those looking for this additional information.
Sunset mitigation: There may be information about possible
mitigation/migration strategies, such as possible ways how
resource users can switch to alternative resources/services.
Any information regarding the above issues (and possibly additional
ones) can be made available through a URI that then can be linked to
using the sunset link relation type. This specification places no
constraints on the scope or the type of the linked resource. The
scope can be for a resource or for a service. The type is determined
by the media type of the linked resource, and can be targeted at
humans, at machines, or a combination of both.
6. IANA Considerations
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6.1. The Sunset Response Header
The Sunset response header should be added to the permanent registry
of message header fields (see [RFC3864]), taking into account the
guidelines given by HTTP/1.1 [RFC7231].
Header Field Name: Sunset
Applicable Protocol: Hypertext Transfer Protocol (HTTP)
Status: Standard
Author/Change controller: IETF
Specification document(s): RFC XXXX
6.2. The Sunset Link Relation Type
The sunset link relation type should be added to the permanent
registry of link relation types according to Section 4.2 of RFC 8288
[RFC8288]:
Relation Name: sunset
Description: Linking to a resource providing information about a
resource's or service's retirement policy and/or information.
Reference: RFC XXXX
7. Implementation Status
Note to RFC Editor: Please remove this section before publication.
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in RFC 6982
[RFC6982]. The description of implementations in this section is
intended to assist the IETF in its decision processes in progressing
drafts to RFCs. Please note that the listing of any individual
implementation here does not imply endorsement by the IETF.
Furthermore, no effort has been spent to verify the information
presented here that was supplied by IETF contributors. This is not
intended as, and must not be construed to be, a catalog of available
implementations or their features. Readers are advised to note that
other implementations may exist.
According to RFC 6982, "this will allow reviewers and working groups
to assign due consideration to documents that have the benefit of
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running code, which may serve as evidence of valuable experimentation
and feedback that have made the implemented protocols more mature.
It is up to the individual working groups to use this information as
they see fit".
Name: https://github.com/hskrasek/guzzle-sunset
Licensing: MIT
Organization: WeWork
Name: https://github.com/wework/faraday-sunset
Licensing: MIT
Description: A Ruby gem adding HTTP client middleware for Sunset
to Faraday
Organization: WeWork
Name: https://github.com/wework/rails-sunset
Licensing: MIT
Description: Create shortcuts for backend developers to use Sunset
(The Rails Way).
8. Security Considerations
The Sunset header field should be treated as a resource hint, meaning
that the resource is indicating its potential retirement. The
definitive test whether or not the resource in fact is available or
not will be to attempt to interact with it. Applications should
never treat an advertised Sunset date as a definitive prediction that
is going to happen at the specified point in time. The Sunset
indication may have been inserted by an intermediary, or the
advertised date may get changed or withdrawn by the resource owner.
The main purpose of the Sunset header field is to signal intent, so
that applications using resources may get a warning ahead of time and
can react accordingly. What an appropriate reaction is (such as
switching to a different resource or service), what it will be based
on (such as machine-readable formats that allow the switching to be
done automatically), and when it will happen (such as ahead of the
advertised date or only when the resource in fact becomes
unavailable) is outside the scope of this specification.
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9. Example
Assuming that a resource has been created in an archive that for
management or compliance reasons only stores resources for two years,
and permanently deletes them afterwards, then the Sunset header field
can be used to expose this information. If such a resource has been
created on November 11, 2014, then the following header field can be
included in responses:
Sunset: Fri, 11 Nov 2018 11:11:11 GMT
This allows clients that are aware of the Sunset header field to
understand that the resource likely will become unavailable at the
specified point in time. Clients can decide to ignore this
information, adjust their own behavior accordingly, or alert
applications or users about this timestamp.
Even though the Sunset header information is made available by the
resource itself, there is no guarantee that the resource indeed will
become unavailable, and if so, how the response will look like for
requests made after that timestamp. In case of the archive used as
an example here, the resource indeed may be permanently deleted, and
requests for the URI after the Sunset timestamp may receive a "410
Gone" HTTP response. (This is assuming that the archive keeps track
of the URIs that it had previously assigned; if not, the response may
be a more generic "404 Not Found".)
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90, RFC 3864,
September 2004.
[RFC7231] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
(HTTP/1.1): Semantics and Content", RFC 7231, June 2014.
[RFC8288] Nottingham, M., "Web Linking", RFC 8288,
DOI 10.17487/RFC8288, October 2017,
<https://www.rfc-editor.org/info/rfc8288>.
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10.2. Informative References
[RFC6982] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", RFC 6982, July
2013.
[RFC7234] Fielding, R., Nottingham, M., and J. Reschke, "Hypertext
Transfer Protocol (HTTP/1.1): Caching", RFC 7234, June
2014.
Appendix A. Acknowledgements
Thanks for comments and suggestions provided by Phil Sturgeon and
Asbjoern Ulsberg.
Author's Address
Erik Wilde
CA Technologies
Email: erik.wilde@dret.net
URI: http://dret.net/netdret/
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