Advanced Message Queuing Protocol (AMQP) Enforcing Connection Uniqueness. Version 1.0

Advanced Message Queuing Protocol (AMQP) Enforcing Connection Uniqueness Version 1.0

The Advanced Message Queuing Protocol (AMQP) is an open internet protocol for business messaging. This document defines a mechanism by which two processes communicating using AMQP v1.0 can ensure and enforce that there exists only a single open AMQP connection between the two of them.

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←1 Introduction

←1.1 IPR Policy

←1.2 Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this specification are to be interpreted as described in [RFC2119] and [RFC8174] when, and only when, they appear in all capitals, as shown here.

The authoritative form of this specification consists of a set of XML source documents. These documents are transformed into PDF and HTML representations for readability. The machine readable version of the AMQP DTD describes the XML used for the authoritative source documents. This DTD includes the definition of the syntax used any excerpts of XML presented in the PDF and HTML representations.

←1.3 Normative References

[AMQP]
Godfrey, Robert; Ingham, David; Schloming, Rafael, Advanced Message Queuing Protocol (AMQP) Version 1.0. October 2012, OASIS Standard.
<http://docs.oasis-open.org/amqp/core/v1.0/os/amqp-core-overview-v1.0-os.html>

[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP14, RFC2119, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>

[RFC8174]
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC2119 Key Words", BCP14, RFC8174, DOI 10.17487/RFC8174, May 2017,
<http://www.rfc-editor.org/info/rfc8174>

←1.4 Non Normative References

[AMQPCONNCAP]
AMQP Capabilities Registry: Connection Capabilities
http://www.amqp.org/specification/1.0/connection-capabilities

[AMQPCONNPROP]
AMQP Capabilities Registry: Connection Properties
http://www.amqp.org/specification/1.0/connection-properties

←2 Overview

AMQP connections are established between containers. On sending the initial open performative, each peer indicates its own container-id in the container-id field of open. The container-id is intended to uniquely identify the container amongst all containers that may establish connections to each other.

It is permitted for multiple connections to be open between two given containers at any given time. While this behavior is generally useful (for instance to allow load balancing across multiple network paths), in certain use cases it is important for the communicating peers to ensure that there is at most one open connection between them.

This document defines how an AMQP container may advertise its ability to detect multiple connections from the same peer, and how its partner may use this ability to request action to remedy the situation such that only one connection remains.

←2.1 Dealing With Duplicates

There are essentially two behaviors that a container can implement to deal with unexpected duplicate connections from the same source:

refuse the new attempt to connect to the container
close the existing connection and admit the new connection

A container complying with this specification MUST be capable of supporting both these behaviors. The behavior the container detecting the duplicates uses MUST be determined by the behavior desired by its partner.

←3 Duplicate Connection Detection

Within this section we shall use the term requesting container to denote the container which is requesting that its partner detect duplicate connections. We shall use the term enforcing container to denote the container which will detect the duplicate connections and perform any necessary enforcement actions.

Note that it is technically possible (though of dubious functional value) for both containers involved in the connection to be acting as both the requesting container and enforcing container simultaneously. Each container independently indicates its ability to perform the role of enforcer and its desire for its partner to do so.

←3.1 Connection Capabilities

Name Description

sole-connection-for-container If present in the desired-capabilities field of open then the sender of open desires to act as the requesting container.

If present in the offered-capabilities field of open then the sender of open performative supports detecting whether multiple connections from the same source container have been opened (i.e. the container is capable of acting as the enforcing container).

The behavior the enforcing container MUST take on detecting a duplicate is determined by the value (if any) associated with the property sole-connection-enforcement-policy in the properties field of open sent by the requesting container.

Name	Description
sole-connection-for-container	If present in the `desired-capabilities` field of `open` then the sender of `open` desires to act as the requesting container. If present in the `offered-capabilities` field of `open` then the sender of `open` performative supports detecting whether multiple connections from the same source container have been opened (i.e. the container is capable of acting as the enforcing container). The behavior the enforcing container MUST take on detecting a duplicate is determined by the value (if any) associated with the property sole-connection-enforcement-policy in the `properties` field of `open` sent by the requesting container.

←3.2 Connection Properties

Name Description

sole-connection-enforcement-policy If present in the properties field of open sent by the requesting container the value determines the action the enforcing container MUST take upon detecting that this connection is a duplicate. The value associated with this property MUST be of type sole-connection-enforcement-policy. If the property is not present, the enforcing container MUST use the sole-connection-enforcement-policy policy.

sole-connection-detection-policy If present in the properties field of open sent by the enforcing container the value indicates its behavior when not all connections from the requesting container indicate the same requirements with regard to duplicate detection. The value associated with this property MUST be of type sole-connection-detection-policy. If the property is not present in the properties field of open sent by the enforcing container then the requesting container can assume sole-connection-detection-policy detection.

Name	Description
sole-connection-enforcement-policy	If present in the `properties` field of `open` sent by the requesting container the value determines the action the enforcing container MUST take upon detecting that this connection is a duplicate. The value associated with this property MUST be of type sole-connection-enforcement-policy. If the property is not present, the enforcing container MUST use the sole-connection-enforcement-policy policy.
sole-connection-detection-policy	If present in the `properties` field of `open` sent by the enforcing container the value indicates its behavior when not all connections from the requesting container indicate the same requirements with regard to duplicate detection. The value associated with this property MUST be of type sole-connection-detection-policy. If the property is not present in the `properties` field of `open` sent by the enforcing container then the requesting container can assume sole-connection-detection-policy detection.

←3.2.1 Sole Connection Enforcement Policy

Defines the action the enforcing container MUST take if it detects that there is an already existing connection between the two containers.

refuse-connection		0
Upon detecting the existence of an existing connection, the enforcing container will refuse the opening of a new connection. If the enforcing container has not already sent the `open` for the connection, it MUST add the property amqp:connection-establishment-failed to the `properties` field of `open` having boolean value true. The enforcing container MUST then immediately send a `close` and the `error` field of `close` MUST have an `error` with the `condition` field of `error` being `invalid-field` and the `info` field of `error` having the `symbol` key invalid-field taking the `symbol` value container-id.
close-existing		1
Upon detecting the existence of an existing connection, the enforcing container will close the existing connection before opening the new one. The existing connection MUST be closed with the `error` field of `close` having the `condition` field of `error` being `resource-locked`. Further the `info` field of `error` MUST contain the `symbol` key sole-connection-enforcement taking the `boolean` value true.

←3.2.2 Sole Connection Detection Policy

Defines the action the enforcing container takes if not all connections between the two containers establish the same sole connection enforcement.

strong		0
If the enforcing container uses the strong detection policy then for every connection which is established, the enforcing container will check to see if a connection already exists between the two containers which has a sole connection enforcement requirement (even if the new connection does not state such a requirement). In such cases, the policy of the existing connection will be enforced. If any connections do exist between the two containers, but they do not have a sole connection enforcement requirement, then any sole connection enforcement policy of the new connection will be applied (if present).
weak		1
If the enforcing container uses the weak detection policy then duplicate detection is only carried out when the new connection requires sole connection enforcement. In this case it is possible that an existing connection which was established with a sole connection detection requirement will no longer be the sole connection between the two containers, as a subsequent connection may not trigger duplicate detection.

Revision	Date	Editor	Changes Made
WD01	23-Mar-2017	Rob Godfrey	Initial Revision
WD02	13-Apr-2017	Rob Godfrey	AMQP-113 : Fix typos, and add clarification
WD03	6-Oct-2017	Rob Godfrey	AMQP-123 : Fix typos AMQP-125 : Add a (minimal) conformance section AMQP-126 : Clarify the strong sole-connection-detection-policy
WD04	20-Apr-2018	Rob Godfrey	AMQP-123 : Fix typos Update conformance section
WD05	15-Jun-2018	Rob Godfrey	Fix typos remove reference to the undefined 'AMQP Network'

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