One document matched: draft-nottingham-http-stale-controls-00.txt
Network Working Group M. Nottingham
Internet-Draft Yahoo! Inc.
Intended status: Informational November 29, 2008
Expires: June 2, 2009
HTTP Cache-Control Extensions for Stale Content
draft-nottingham-http-stale-controls-00
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on June 2, 2009.
Abstract
This document defines two independent HTTP Cache-Control extensions
that allow control over the use of stale responses by caches.
Nottingham Expires June 2, 2009 [Page 1]
Internet-Draft HTTP stale controls November 2008
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 3
3. The stale-while-revalidate Cache-Control Extension . . . . . . 3
3.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. The stale-if-error Cache-Control Extension . . . . . . . . . . 4
4.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
7. Normative References . . . . . . . . . . . . . . . . . . . . . 6
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 6
Intellectual Property and Copyright Statements . . . . . . . . . . 8
Nottingham Expires June 2, 2009 [Page 2]
Internet-Draft HTTP stale controls November 2008
1. Introduction
HTTP [RFC2616] requires that caches "respond to a request with the
most up-to-date response held... that is appropriate to the request,"
although "in carefully controlled circumstances" a stale response is
allowed to be returned. This document defines two independent Cache-
Control extensions that allow for such control, stale-if-error and
stale-while-revalidate.
The stale-if-error HTTP Cache-Control extension allows a cache to
return a stale response when an error -- e.g., a 500 Internal Server
Error, a network segment, or DNS failure -- is encountered, rather
than returning a "hard" error. This improves availability.
The stale-while-revalidate HTTP Cache-Control extension allows a
cache to immediately return a stale response while it revalidates it
in the background, thereby hiding latency (both in the network and on
the server) from clients.
2. Notational Conventions
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].
This specification uses the augmented Backus-Naur Form of RFC2616
[RFC2616], and includes the delta-seconds rule from that
specification.
3. The stale-while-revalidate Cache-Control Extension
When present in an HTTP response, the stale-while-revalidate Cache-
Control extension indicates that caches MAY serve the response it
appears in after it becomes stale, up to the indicated number of
seconds.
stale-while-revalidate = "stale-while-revalidate" "=" delta-seconds
If a cached response is served stale due to the presence of this
extension, the cache SHOULD attempt to revalidate it while still
serving stale responses (i.e., without blocking).
Note that "stale" implies that the response will have a non-zero Age
header and a warning header, as per HTTP's requirements.
If delta-seconds passes without the cached entity being revalidated,
Nottingham Expires June 2, 2009 [Page 3]
Internet-Draft HTTP stale controls November 2008
it SHOULD NOT continue to be served stale, absent other information.
3.1. Example
A response containing:
Cache-Control: max-age=600, stale-while-revalidate=30
indicates that it is fresh for 600 seconds, and it may continue to be
served stale for up to an additional 30 seconds while an asynchronous
validation is attempted. If validation is inconclusive, or if there
is not traffic that triggers it, after 30 seconds the stale-while-
revalidate function will cease to operate, and the cached response
will be "truly" stale (i.e., the next request will block and be
handled normally).
Generally, servers will want to set the combination of max-age and
stale-while-revalidate to the longest total potential freshness
lifetime that they can tolerate. For example, with both set to 600,
the server must be able to tolerate the response being served from
cache for up to 20 minutes.
Since asynchronous validation will only happen if a request occurs
after the response has become stale, but before the end of the stale-
while-revalidate window, the size of that window and the likelihood
of a request during it determines how likely it is that all requests
will be served without delay. if the window is too small, or traffic
too sparse, some requests will fall outside of it, and block until
the server can validate the cached response.
4. The stale-if-error Cache-Control Extension
The stale-if-error Cache-Control extension indicates that when an
error is encountered, a cached stale response MAY be used to satisfy
the request, regardless of other freshness information.
stale-if-error = "stale-if-error" "=" delta-seconds
When used as a request Cache-Control extension, its scope of
application is the request it appears in; when used as a response
Cache-Control extension, its scope is any request applicable to the
cached response it occurs in.
Its value indicates the upper limit to staleness; when the cached
response is more stale than the indicated amount, the cached response
SHOULD NOT be used to satisfy the request, absent other information.
Nottingham Expires June 2, 2009 [Page 4]
Internet-Draft HTTP stale controls November 2008
In this context, an error is any situation which would result in a
500, 502, 503 or 504 HTTP response status code being returned.
Note that this directive does not affect freshness; stale cached
responses that are used SHOULD still be visibly stale when sent
(i.e., have a non-zero Age header and a warning header, as per HTTP's
requirements.).
4.1. Example
A response containing:
HTTP/1.1 200 OK
Cache-Control: max-age=600, stale-if-error=1200
Content-Type: text/plain
success
indicates that it is fresh for 600 seconds, and that it may be used
if an error is encountered after becoming stale for an additional
1200 seconds.
Thus, if the cache attempts to validate 900 seconds afterwards and
encounters:
HTTP/1.1 500 Internal Server Error
Content-Type: text/plain
failure
the successful response can be returned instead:
HTTP/1.1 200 OK
Cache-Control: max-age=600, stale-if-error=1200
Age: 900
Content-Type: text/plain
succcess
After the age is greater than 1800 seconds (i.e., it has been stale
for 1200 seconds), the cache must write the error message through.
HTTP/1.1 500 Internal Server Error
Content-Type: text/plain
failure
Nottingham Expires June 2, 2009 [Page 5]
Internet-Draft HTTP stale controls November 2008
5. Security Considerations
The stale-while-revalidate extension provides origin servers with a
mechanism for dictating that stale content should be served from
caches under certain circumstances, with the expectation that the
cached response will be revalidated in the background. It is
suggested that such validation be predicated upon an incoming
request, to avoid the possibility of an amplification attack (as can
be seen in some other pre-fetching and automatic refresh mechanisms).
Cache implementers should keep this in mind when deciding the
circumstances under which they will generate a request that is not
directly initiated by a user or client.
The stale-if-error provides origin servers and clients a mechanism
for dictating that stale content should be served from caches under
certain circumstances, and does not pose additional security
considerations over those of RFC2616, which also allows stale content
to be served.
6. IANA Considerations
This document has no actions for IANA.
7. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
Appendix A. Acknowledgements
Thanks to Ben Drees, John Nienart, Henrik Nordstrom, Evan Torrie, and
Chris Westin for their suggestions. The author takes all
responsibility for errors and omissions.
Nottingham Expires June 2, 2009 [Page 6]
Internet-Draft HTTP stale controls November 2008
Author's Address
Mark Nottingham
Yahoo! Inc.
Email: mnot@yahoo-inc.com
URI: http://www.mnot.net/
Nottingham Expires June 2, 2009 [Page 7]
Internet-Draft HTTP stale controls November 2008
Full Copyright Statement
Copyright (C) The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Nottingham Expires June 2, 2009 [Page 8]
| PAFTECH AB 2003-2026 | 2026-04-24 13:33:19 |