draft-ietf-httpapi-ratelimit-headers-02.unpg.txt		draft-ietf-httpapi-ratelimit-headers-latest.txt
	HTTPAPI Working Group R. Polli		HTTPAPI Working Group R. Polli
	Internet-Draft Team Digitale, Italian Government		Internet-Draft Team Digitale, Italian Government
	Intended status: Standards Track A. Martinez		Intended status: Standards Track A. Martinez
	Expires: May 14, 2022 Red Hat		Expires: July 30, 2022 Red Hat
	November 10, 2021		January 26, 2022
	RateLimit Fields for HTTP		RateLimit Fields for HTTP
	draft-ietf-httpapi-ratelimit-headers-02		draft-ietf-httpapi-ratelimit-headers-latest
	Abstract		Abstract
	This document defines the RateLimit-Limit, RateLimit-Remaining,		This document defines the RateLimit-Limit, RateLimit-Remaining,
	RateLimit-Reset fields for HTTP, thus allowing servers to publish		RateLimit-Reset fields for HTTP, thus allowing servers to publish
	current service limits and clients to shape their request policy and		current service limits and clients to shape their request policy and
	avoid being throttled out.		avoid being throttled out.
	Note to Readers		Note to Readers
	skipping to change at line 47 ¶		skipping to change at page 1, line 48 ¶
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at https://datatracker.ietf.org/drafts/current/.		Drafts is at https://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on May 14, 2022.		This Internet-Draft will expire on July 30, 2022.
	Copyright Notice		Copyright Notice
	Copyright (c) 2021 IETF Trust and the persons identified as the		Copyright (c) 2022 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
	(https://trustee.ietf.org/license-info) in effect on the date of		(https://trustee.ietf.org/license-info) in effect on the date of
	publication of this document. Please review these documents		publication of this document. Please review these documents
	carefully, as they describe your rights and restrictions with respect		carefully, as they describe your rights and restrictions with respect
	to this document. Code Components extracted from this document must		to this document. Code Components extracted from this document must
	include Simplified BSD License text as described in Section 4.e of		include Simplified BSD License text as described in Section 4.e of
	the Trust Legal Provisions and are provided without warranty as		the Trust Legal Provisions and are provided without warranty as
	described in the Simplified BSD License.		described in the Simplified BSD License.
	Table of Contents
	1. Introduction
	1.1. Goals
	1.2. Notational Conventions
	2. Expressing rate-limit policies
	2.1. Time window
	2.2. Service limit
	2.3. Quota policy
	3. Providing RateLimit fields
	3.1. Performance considerations
	4. Receiving RateLimit fields
	4.1. Intermediaries
	4.2. Caching
	5. Fields definition
	5.1. RateLimit-Limit
	5.2. RateLimit-Remaining
	5.3. RateLimit-Reset
	6. Security Considerations
	6.1. Throttling does not prevent clients from issuing requests
	6.2. Information disclosure
	6.3. Remaining quota-units are not granted requests
	6.4. Reliability of RateLimit-Reset
	6.5. Resource exhaustion
	6.6. Denial of Service
	7. IANA Considerations
	7.1. RateLimit Parameters Registration
	8. References
	8.1. Normative References
	8.2. Informative References
	8.3. URIs
	Appendix A. Rate-limiting and quotas
	A.1. Interoperability issues
	Appendix B. Examples
	B.1. Unparameterized responses
	B.1.1. Throttling information in responses
	B.1.2. Use in conjunction with custom fields
	B.1.3. Use for limiting concurrency
	B.1.4. Use in throttled responses
	B.2. Parameterized responses
	B.2.1. Throttling window specified via parameter
	B.2.2. Dynamic limits with parameterized windows
	B.2.3. Dynamic limits for pushing back and slowing down
	B.3. Dynamic limits for pushing back with Retry-After and slow
	down
	B.3.1. Missing Remaining information
	B.3.2. Use with multiple windows
	Appendix C. Acknowledgements
	Appendix D. FAQ
	RateLimit fields currently used on the web
	Changes
	F.1. Since draft-ietf-httpapi-ratelimit-headers-01
	F.2. Since draft-ietf-httpapi-ratelimit-headers-00
	Authors' Addresses
	1. Introduction		1. Introduction
	The widespreading of HTTP as a distributed computation protocol		The widespreading of HTTP as a distributed computation protocol
	requires an explicit way of communicating service status and usage		requires an explicit way of communicating service status and usage
	quotas.		quotas.
	This was partially addressed by the "Retry-After" header field		This was partially addressed by the "Retry-After" header field
	defined in [SEMANTICS] to be returned in "429 Too Many Requests" (see		defined in [SEMANTICS] to be returned in "429 Too Many Requests" (see
	[STATUS429]) or "503 Service Unavailable" responses.		[STATUS429]) or "503 Service Unavailable" responses.
	skipping to change at line 176 ¶		skipping to change at page 3, line 31 ¶
	include detailed quota limits and related fields in API		include detailed quota limits and related fields in API
	documentation.		documentation.
	The following features are out of the scope of this document:		The following features are out of the scope of this document:
	Authorization: RateLimit fields are not meant to support		Authorization: RateLimit fields are not meant to support
	authorization or other kinds of access controls.		authorization or other kinds of access controls.
	Throttling scope: This specification does not cover the throttling		Throttling scope: This specification does not cover the throttling
	scope, that may be the given resource-target, its parent path or		scope, that may be the given resource-target, its parent path or
	the whole Origin (see Section 7 of [RFC6454]).		the whole Origin (see Section 7 of [RFC6454]). This can be
			addressed using extensibility mechanisms such as the parameter
			registry Section 7.1.
	Response status code: RateLimit fields may be returned in both		Response status code: RateLimit fields may be returned in both
	successful (see Section 15.3 of [SEMANTICS]) and non-successful		successful (see Section 15.3 of [SEMANTICS]) and non-successful
	responses. This specification does not cover whether non		responses. This specification does not cover whether non
	Successful responses count on quota usage, nor it mandates any		Successful responses count on quota usage, nor it mandates any
	correlation between the RateLimit values and the returned status		correlation between the RateLimit values and the returned status
	code.		code.
	Throttling policy: This specification does not mandate a specific		Throttling policy: This specification does not mandate a specific
	throttling policy. The values published in the fields, including		throttling policy. The values published in the fields, including
	skipping to change at line 243 ¶		skipping to change at page 5, line 8 ¶
	requests that the server is willing to accept from one or more		requests that the server is willing to accept from one or more
	clients on a given basis (originating IP, authenticated user,		clients on a given basis (originating IP, authenticated user,
	geographical, ..) during a "time-window" as defined in Section 2.1.		geographical, ..) during a "time-window" as defined in Section 2.1.
	The "service-limit" is expressed in "quota-units" and has the		The "service-limit" is expressed in "quota-units" and has the
	following syntax:		following syntax:
	service-limit = quota-units		service-limit = quota-units
	quota-units = sf-integer		quota-units = sf-integer
	where quota-units is a non-negative sf-integer.		where "quota-units" is a non-negative sf-integer.
	The "service-limit" SHOULD match the maximum number of acceptable		The "service-limit" SHOULD match the maximum number of acceptable
	requests.		requests.
	The "service-limit" MAY differ from the total number of acceptable		The "service-limit" MAY differ from the total number of acceptable
	requests when weight mechanisms, bursts, or other server policies are		requests when weight mechanisms, bursts, or other server policies are
	implemented.		implemented.
	If the "service-limit" does not match the maximum number of		If the "service-limit" does not match the maximum number of
	acceptable requests the relation with that SHOULD be communicated		acceptable requests the relation with that SHOULD be communicated
	skipping to change at line 280 ¶		skipping to change at page 5, line 45 ¶
	This specification allows describing a quota policy with the		This specification allows describing a quota policy with the
	following syntax:		following syntax:
	quota-policy = sf-item		quota-policy = sf-item
	where the associated bare-item is a service-limit and parameters are		where the associated bare-item is a service-limit and parameters are
	supported.		supported.
	The following parameters are defined:		The following parameters are defined:
	w: The "w" parameter specifies a time window. Its syntax is a "time-		w: The REQUIRED "w" parameter specifies a time window. Its syntax is
	window" defined in Section 2.1.		a "time-window" defined in Section 2.1.
	Other parameters are allowed and can be regarded as comments. They		Other parameters are allowed and can be regarded as comments. They
	ought to be registered within the "Hypertext Transfer Protocol (HTTP)		ought to be registered within the "Hypertext Transfer Protocol (HTTP)
	RateLimit Parameters Registry", as described in Section 7.1.		RateLimit Parameters Registry", as described in Section 7.1.
	An example policy of 100 quota-units per minute.		An example policy of 100 quota-units per minute.
	100;w=60		100;w=60
	The definition of a quota-policy does not imply any specific		The definition of a quota-policy does not imply any specific
	distribution of quota-units over time. Such service specific details		distribution of quota-units over time. Such service specific details
	can be conveyed as parameters.		can be conveyed as parameters.
	Two examples of providing further details via custom parameters		Two policy examples containing further details via custom parameters
	100;w=60;comment="fixed window"		100;w=60;comment="fixed window"
	12;w=1;burst=1000;policy="leaky bucket"		12;w=1;burst=1000;policy="leaky bucket"
			To avoid clashes, implementers SHOULD prefix unregistered parameters
			with an "x-<vendor>" identifier, e.g. "x-acme-policy", "x-acme-
			burst". While it is useful to define a clear syntax and semantics
			even for custom parameters, it is important to note that user agents
			are not required to process quota policy information.
	3. Providing RateLimit fields		3. Providing RateLimit fields
	A server MAY use one or more "RateLimit" response fields defined in		A server uses the "RateLimit" response fields defined in this
	this document to communicate its quota policies.		document to communicate its quota policies according to the following
			rules:
			o "RateLimit-Limit" and "RateLimit-Reset" are REQUIRED;
			o "RateLimit-Remaining" is RECOMMENDED.
	The returned values refers to the metrics used to evaluate if the		The returned values refers to the metrics used to evaluate if the
	current request respects the quota policy and MAY not apply to		current request respects the quota policy and MAY not apply to
	subsequent requests.		subsequent requests.
	Example: a successful response with the following fields		Example: a successful response with the following fields
	RateLimit-Limit: 10		RateLimit-Limit: 10
	RateLimit-Remaining: 1		RateLimit-Remaining: 1
	RateLimit-Reset: 7		RateLimit-Reset: 7
	skipping to change at line 361 ¶		skipping to change at page 7, line 41 ¶
	Under certain conditions, a server MAY artificially lower "RateLimit"		Under certain conditions, a server MAY artificially lower "RateLimit"
	field values between subsequent requests, e.g. to respond to Denial		field values between subsequent requests, e.g. to respond to Denial
	of Service attacks or in case of resource saturation.		of Service attacks or in case of resource saturation.
	Servers usually establish whether the request is in-quota before		Servers usually establish whether the request is in-quota before
	creating a response, so the RateLimit field values should be already		creating a response, so the RateLimit field values should be already
	available in that moment. Nonetheless servers MAY decide to send the		available in that moment. Nonetheless servers MAY decide to send the
	"RateLimit" fields in a trailer section.		"RateLimit" fields in a trailer section.
			To ease the migration from existing rate limit headers, a server
			SHOULD be able to provide the "RateLimit-Limit" field even without
			the optional "quota-policy" section.
	3.1. Performance considerations		3.1. Performance considerations
	Servers are not required to return "RateLimit" fields in every		Servers are not required to return "RateLimit" fields in every
	response, and clients need to take this into account. For example,		response, and clients need to take this into account. For example,
	an implementer concerned with performance might provide "RateLimit"		an implementer concerned with performance might provide "RateLimit"
	fields only when a given quota is going to expire.		fields only when a given quota is going to expire.
	Implementers concerned with response fields' size, might take into		Implementers concerned with response fields' size, might take into
	account their ratio with respect to the payload data, or use header-		account their ratio with respect to the payload data, or use header-
	compression http features such as [HPACK].		compression http features such as [HPACK].
	skipping to change at line 1222 ¶		skipping to change at page 26, line 18 ¶
	Response:		Response:
	HTTP/1.1 200 OK		HTTP/1.1 200 OK
	Content-Type: application/json		Content-Type: application/json
	RateLimit-Limit: 5000, 1000;w=3600, 5000;w=86400		RateLimit-Limit: 5000, 1000;w=3600, 5000;w=86400
	RateLimit-Remaining: 100		RateLimit-Remaining: 100
	RateLimit-Reset: 36000		RateLimit-Reset: 36000
	{"hello": "world"}		{"hello": "world"}
	Appendix C. Acknowledgements		FAQ
	Thanks to Willi Schoenborn, Alejandro Martinez Ruiz, Alessandro
	Ranellucci, Amos Jeffries, Martin Thomson, Erik Wilde and Mark
	Nottingham for being the initial contributors of these
	specifications. Kudos to the first community implementers: Aapo
	Talvensaari, Nathan Friedly and Sanyam Dogra.
	Appendix D. FAQ		_RFC Editor: Please remove this section before publication._
	1. Why defining standard fields for throttling?		1. Why defining standard fields for throttling?
	To simplify enforcement of throttling policies.		To simplify enforcement of throttling policies.
	2. Can I use RateLimit-* in throttled responses (eg with status code		2. Can I use RateLimit-* in throttled responses (eg with status code
	429)?		429)?
	Yes, you can.		Yes, you can.
	skipping to change at line 1253 ¶		skipping to change at page 26, line 43 ¶
	No. [RFC6585] defines the "429" status code and we use it just		No. [RFC6585] defines the "429" status code and we use it just
	as an example of a throttled request, that could instead use even		as an example of a throttled request, that could instead use even
	"403" or whatever status code. The goal of this specification is		"403" or whatever status code. The goal of this specification is
	to standardize the name and semantic of three ratelimit fields		to standardize the name and semantic of three ratelimit fields
	widely used on the internet. Stricter relations with status		widely used on the internet. Stricter relations with status
	codes or error response payloads would impose behaviors to all		codes or error response payloads would impose behaviors to all
	the existing implementations making the adoption more complex.		the existing implementations making the adoption more complex.
	4. Why don't pass the throttling scope as a parameter?		4. Why don't pass the throttling scope as a parameter?
	After a discussion on a similar thread [4] we will probably add a		The word "scope" can have different meanings: for example it can
	new "RateLimit-Scope" field to this spec.		be an URL, or an authorization scope. Since authorization is out
			of the scope of this document (see Section 1.1), and that we rely
			only on [SEMANTICS], in Section 1.1 we defined "scope" in terms
			of URL.
	I'm open to suggestions: comment on this issue [5]		Since clients are not required to process quota policies (see
			Section 4), we could add a new "RateLimit-Scope" field to this
			spec. See this discussion on a similar thread [4]
			Specific ecosystems can still bake their own prefixed parameters,
			such as "acme-auth-scope" or "acme-url-scope" and ensure that
			clients process them. This behavior cannot be relied upon when
			communicating between different ecosystems.
			We are open to suggestions: comment on this issue [5]
	5. Why using delay-seconds instead of a UNIX Timestamp? Why not		5. Why using delay-seconds instead of a UNIX Timestamp? Why not
	using subsecond precision?		using subsecond precision?
	Using delay-seconds aligns with "Retry-After", which is returned		Using delay-seconds aligns with "Retry-After", which is returned
	in similar contexts, eg on 429 responses.		in similar contexts, eg on 429 responses.
	Timestamps require a clock synchronization protocol (see		Timestamps require a clock synchronization protocol (see
	Section 5.6.7 of [SEMANTICS]). This may be problematic (e.g.		Section 5.6.7 of [SEMANTICS]). This may be problematic (e.g.
	clock adjustment, clock skew, failure of hardcoded clock		clock adjustment, clock skew, failure of hardcoded clock
	skipping to change at line 1432 ¶		skipping to change at page 30, line 42 ¶
	RateLimit-Reset: 1		RateLimit-Reset: 1
	If this is the case, the optimal solution is to achieve		If this is the case, the optimal solution is to achieve
	RateLimit-Limit: 12, 12;w=1		RateLimit-Limit: 12, 12;w=1
	RateLimit-Remaining: 1 ; using 100% of throughput, that is 12 units/s		RateLimit-Remaining: 1 ; using 100% of throughput, that is 12 units/s
	RateLimit-Reset: 1		RateLimit-Reset: 1
	At this point you should stop increasing your request rate.		At this point you should stop increasing your request rate.
			Acknowledgements
			Thanks to Willi Schoenborn, Alejandro Martinez Ruiz, Alessandro
			Ranellucci, Amos Jeffries, Martin Thomson, Erik Wilde and Mark
			Nottingham for being the initial contributors of these
			specifications. Kudos to the first community implementers: Aapo
			Talvensaari, Nathan Friedly and Sanyam Dogra.
			In addition to the people above, this document owes a lot to the
			extensive discussion in the HTTPAPI workgroup, including Rich Salz,
			Darrel Miller and Julian Reschke.
	Changes		Changes
	_RFC Editor: Please remove this section before publication._		_RFC Editor: Please remove this section before publication._
	F.1. Since draft-ietf-httpapi-ratelimit-headers-01		F.1. Since draft-ietf-httpapi-ratelimit-headers-01
	o Update IANA considerations #60		o Update IANA considerations #60
	o Use Structured fields #58		o Use Structured fields #58
End of changes. 17 change blocks.
	78 lines changed or deleted		57 lines changed or added
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