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Endpoint Registry Service - Version 1.0-rc1

Abstract

This specification defines an endpoint registry extension to the xRegistry document format and API specification.

Table of Contents

Overview

This specification defines a registry of metadata definitions for abstract and concrete network endpoints to which messages can be produced, from which messages can be consumed, or which make messages available for subscriptions.

For easy reference, the JSON serialization of an Endpoint Registry adheres to this form:

{
  "specversion": "STRING",
  "registryid": "STRING",
  "self": "URL",
  "xid": "XID",
  "epoch": UINTEGER,
  "name": "STRING", ?
  "description": "STRING", ?
  "documentation": "URL", ?
  "labels": {
    "STRING": "STRING" *
  }, ?
  "createdat": "TIMESTAMP",
  "modifiedat": "TIMESTAMP",

  "model": { ... }, ?

  "endpointsurl": "URL",
  "endpointscount": UINTEGER,
  "endpoints": {
    "KEY": {
      "endpointid": "STRING",                   # xRegistry core attributes
      "self": "URL",
      "xid": "XID",
      "epoch": UINTEGER,
      "name": "STRING", ?
      "description": "STRING", ?
      "documentation": "URL", ?
      "labels": { "STRING": "STRING" * }, ?
      "createdat": "TIMESTAMP",
      "modifiedat": "TIMESTAMP",

      # Start of default Version's attributes
      "usage": "STRING",                        # subscriber, consumer, producer
      "channel": "STRING", ?
      "deprecated": {
        "effective": "TIMESTAMP", ?
        "removal": "TIMESTAMP", ?
        "alternative": "URL", ?
        "docs": "URL"?
      }, ?

      "envelope": "STRING", ?                   # e.g. CloudEvents/1.0
      "envelopeoptions": {
        "STRING": JSON-VALUE *

        # CloudEvents/1.0 options
        "mode": "STRING", ?                     # binary, structured
        "format": "STRING" ?                    # e.g. application/json
      },

      "protocol": "STRING", ?                   # e.g. HTTP/1.1
      "protocoloptions": {
        "STRING": JSON-VALUE *

        # Common protocol options
        "endpoints": [
          {
            "url": "URL"                        # plus endpoint extensions
          } *
        ], ?
        "authorization": {
          "type": "STRING", ?
          "resourceuri": "URI", ?
          "authorityuri": "URI", ?
          "grant_types": [ "STRING" * ] ?
        }, ?
        "deployed": BOOLEAN, ?

        # "HTTP" protocol options
        "method": "STRING", ?                          # Default: POST
        "headers": [ { "name": "STRING", "value": "STRING" } * ], ?
        "query": { "STRING": "STRING" * } ?

        # "AMQP/1.0" protocol options
        "node": "STRING", ?
        "durable": BOOLEAN, ?                          # Default: false
        "linkproperties": { "STRING": "STRING" * }, ?
        "connectionproperties": { "STRING": "STRING" * }, ?
        "distributionmode": "move" | "copy" ?          # Default: move

        # "MQTT/3.1.1" protocol options
        "topic": "STRING", ?
        "qos": UINTEGER, ?                             # Default: 0
        "retain": BOOLEAN, ?                           # Default: false
        "cleansession": BOOLEAN, ?                     # Default: true
        "willtopic": "STRING", ?
        "willmessage": "STRING" ?

        # "MQTT/5.0" protocol options
        "topic": "STRING", ?
        "qos": UINTEGER, ?                             # Default: 0
        "retain": BOOLEAN, ?                           # Default: false
        "cleansession": BOOLEAN, ?                     # Default: true
        "willtopic": "STRING", ?
        "willmessage": "STRING" ?

        # "KAFKA" protocol options
        "topic": "STRING", ?
        "acks": INTEGER, ?                             # Default: 1
        "key": "STRING", ?
        "partition": INTEGER, ?
        "consumergroup": "STRING", ?
        "headers": { "STRING": "STRING" * } ?

        # "NATS" protocol options
        "subject": "STRING" ?
      }, ?

      "messagegroups": [ URI * ], ?
      # End of default Version's attributes

      "messagesurl": "URL", ?
      "messagescount": UINTEGER, ?
      "messages": {
        "KEY": {                                # messageid
          # See Message Definition spec for details
        } *
      } ?
    } *
  } ?
}

Notations and Terminology

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.

For clarity, OPTIONAL attributes (specification-defined and extensions) are OPTIONAL for clients to use, but the servers' responsibility will vary. Server-unknown extension attributes MUST be silently stored in the backing datastore. Specification-defined, and server-known extension, attributes MUST generate an error if corresponding feature is not supported or enabled. However, as with all attributes, if accepting the attribute would result in a bad state (such as exceeding a size limit, or results in a security issue), then the server MAY choose to reject the request.

In the pseudo JSON format snippets ? means the preceding attribute is OPTIONAL, * means the preceding attribute MAY appear zero or more times, and + means the preceding attribute MUST appear at least once. The presence of the # character means the remaining portion of the line is a comment. Whitespace characters in the JSON snippets are used for readability and are not normative.

Terminology

This specification defines the following terms:

Endpoint

An "endpoint" is a logical or physical network location to which messages can be produced, from which messages can be consumed, or which makes messages available via subscription for delivery to a consumer-designated endpoint.

Endpoint Registry

The Endpoint Registry is a registry of metadata definitions for abstract and concrete network endpoints to which messages can be produced, from which messages can be consumed, or which makes messages available via subscription and delivery to a consumer-designated endpoint.

As discussed in CloudEvents Registry overview, endpoints are supersets of message definition groups and MAY contain inlined messages. Therefore, the Resources in the meta-model for the Endpoint Registry are likewise messages as defined in the message catalog specification.

The resource model for endpoints can be found in model.json.

Endpoints

Endpoints are a Group type with a plural name (GROUPS) of endpoints, and a singular name (GROUP) of endpoint.

The following attributes are defined for Endpoints:

usage

  • Type: String (Enum: subscriber, consumer, producer)

  • Description: The usage attribute is a string that indicates the intended usage of the endpoint by communicating parties. In other words, the role of a client talking with the endpoint.

    Each of these parties will have a different perspective on an endpoint. For instance, a producer endpoint is seen as a "target" by the originator of messages, and as a "source" by the party that accepts the messages. The nomenclature used for the usage field is primarily oriented around the common scenario of network endpoints being provided by some sort of intermediary like a message broker. The term producer primarily describes the relationship of a client with that intermediary.

    In a direct-delivery scenario where the originator of messages connects directly to the target (e.g. a "WebHook" call), the target endpoint implements the accepting end of the producer relationship.

    Some of these perspectives are mentioned below for illustration, but not formally defined or reflected in the metadata model. Perspectives depend on the context in which the endpoint metadata is used and this metadata model is intentionally leaving perspectives open to users.

    The following values are defined for usage

    • subscriber: The endpoint offers managing subscriptions for delivery of messages to another endpoint, using the CloudEvents Subscriptions API.

      Some perspectives that might exist on a subscriber endpoint:

      • Application from which messages originate
      • Application which accepts messages from the delivery agent
      • Application which manages subscriptions for delivery of messages to the target application. This might be a message broker subscription manager.

    • consumer: The endpoint offers messages being consumed (pulled) from it.

      Some perspectives that might exist on a consumer endpoint:

      • Message store or source which makes messages available for consumption; this might be a message broker topic or a queue.
      • Proxy or other intermediary which solicits messages from the source and forwards them to the target endpoint.
      • Application which consumes messages

    • producer: The endpoint offers messages being produced (pushed) to it.

      Some perspectives might exist on a producer endpoint:

      • Application from which messages originate
      • Reverse proxy or other intermediary which accepts messages from the originator and forwards them to the target endpoint.
      • Application which accepts messages. This might be a message broker topic or a queue. This might be an HTTP endpoint that directly accepts and handles messages.

    Any endpoint can be seen from different role perspectives:

    There might also be further perspectives such as pipeline stages for pre-/post-processing, etc.

  • Constraints:

    • REQUIRED
    • MUST be one of "subscriber", "consumer", or "producer".

channel

  • Type: String

  • Description: A string that can be used to correlate Endpoints. Any Endpoints within an instance of an Endpoint Registry that share the same non-empty channel value MUST have some relationship. This specification does not define that relationship or the specific values used in this property. However, it is expected that the usage value in combination with this channel property will provide some information to help determine the relationship.

    For instance, a message broker queue "queue1" might be represented with a producer endpoint and a consumer endpoint, both with the same channel attribute value of "queue1".

    An event processing pipeline might have a sequence of stages, each with a producer endpoint and a consumer endpoint, all with the same channel attribute value of "pipeline1", or some further qualification like "pipeline1-stage1", etc.

    This specification does not make any statement about whether two endpoints that do not share the same non-empty value have any relationship or not. They might, but how this is determined is out of scope of this specification. Additionally, while it is expected that this attribute's value will be a single value, given this specification does not place any constraints on its syntax or semantic meaning, implementations might choose to "encode" multiple values within this single string. That would then imply that the comparison algorithm of two channel values might need to be more complicated than a "string compare" in those cases.

    When this property has no value it MUST either be serialized as an empty string or excluded from the serialization entirely.

  • Constraints:

    • OPTIONAL
    • When specified, the value MUST be a non-empty string

  • Examples:

    • queue1

deprecated

See the deprecated attribute in the core xRegistry specification.

envelope

  • Type: String
  • Description: The name of the specification that defines the Resource stored in the registry. Often it is difficult to unambiguously determine what a Resource is via simple inspect of its serialization. This attribute provides a mechanism by which it can be determined without examination of the Resource at all
  • Constraints:
    • At least one of envelope and protocol MUST be specified
    • MUST be a non-empty string of the form SPEC[/VERSION], where SPEC is the non-empty string name of the specification that defines the Resource. An OPTIONAL VERSION value SHOULD be included if there are multiple versions of the specification available
    • For comparison purposes, this attribute MUST be considered case sensitive
    • If a VERSION is specified at the Group level, all Resources within that Group MUST have a VERSION value that is at least as precise as its Group, and MUST NOT expand it. For example, if a Group had a envelope value of myspec, then Resources within that Group can have envelope values of myspec or myspec/1.0. However, if a Group has a value of myspec/1.0 it would be invalid for a Resource to have a value of myspec/2.0 or just myspec. Additionally, if a Group does not have a envelope attribute then there are no constraints on its Resources envelope attributes
    • This specification places no restriction on the case of the SPEC value or on the syntax of the VERSION value
  • Examples:
    • CloudEvents/1.0

envelopeoptions

  • Type: Map

  • Description: Configuration details of the endpoint with respect to the envelope format use to transmit the messages.

  • Constraints:

    • OPTIONAL

  • Examples:

    • For an endpoint using an envelope value of CloudEvents/1.0: { "mode": "binary", "format": "application/json" }

This specification defines the following envelope options for the indicated envelope values:

CloudEvents/1.0

  • mode : indicates whether the CloudEvent generated will use binary or structured (mode)[https://github.com/cloudevents/spec/blob/main/cloudevents/spec.md#message]. When specified, its value MUST be one of: binary or structured. When not specified, the endpoint is indicating that either mode is acceptable.
  • format : indicates the format of the CloudEvent when sent in structured mode. This attribute MUST NOT be specified when mode is binary. The value used MUST match the expected content type of the message (e.g. for HTTP the Content-Type header value).

protocol

  • Type: String

  • Description: The transport or application protocol used by the endpoint. This specification defines a set of common protocol names that MUST be used for respective protocol endpoints, but implementations MAY define and use additional protocol names.

    An example for an extension protocol identifier might be "BunnyMQ/0.9.1".

    Predefined protocols SHOULD be referred to by name and version as {NAME}/{VERSION}. If the version is not specified, the default version of the protocol is assumed. The version number format is determined by the protocol specification's usage of versions.

    The predefined protocol names are:

    • "HTTP" - Used for HTTP/1.1, HTTP/2, HTTP/3.
    • "AMQP/1.0" - Use the AMQP 1.0 protocol. MAY be shortened to "AMQP". AMQP draft versions before 1.0 (e.g. 0.9) are not AMQP.
    • "MQTT/3.1.1", "MQTT/5.0" - Use the MQTT 3.1.1 or 5.0 protocol. The shorthand "MQTT" maps to "MQTT/5.0".
    • "NATS" - Use the NATS protocol.
    • "KAFKA" - Use the Apache Kafka protocol.

    All messages inside an Endpoint MUST use this same protocol

  • Constraints:

    • At least one of envelope and protocol MUST be specified
    • MUST be a non-empty string
    • SHOULD follow the naming convention {NAME}/{VERSION}, whereby {NAME} is the name of the protocol and {VERSION} is the version of protocol.

  • Examples:

    • MQTT/3.1.1
    • AMQP/1.0
    • KAFKA

protocoloptions

  • Type: Map

  • Description: Configuration details of the endpoint related to the protocol used to transmit the messages. An endpoint MAY be defined without detail configuration. In this case, the endpoint is considered to be "abstract".

  • Constraints:

    • OPTIONAL

protocoloptions.endpoints

  • Type: Array of Objects
  • Description: An array of objects map where each object contains a uri attribute with the the network address to which clients can communicate with the endpoint. The object MAY contain extension attributes that can be used by clients to determine which URI to use, or to configure access to the specific URI. Whether the URI identifies a network host or links directly to a resource managed by the network host is protocol specific.
  • Constraints:
    • OPTIONAL
    • Each object key MUST contain a uri attribute with a valid, absolute URI (URL)
  • Examples:
    • [ {"uri": "https://example.com" } ]
    • [
  { "uri": "tcp://example.com" },
  { "uri": "wss://example.com" }
]

    • [
  {
    "uri": "tcp://example.com",
    "priority": 1,
    "status": "down"
  },
  {
    "uri": "wss://example.com",
    "priority": 2,
    "status": "up"
  }
]

protocoloptions.authorization

  • Type: Map

  • Description: OPTIONAL authorization configuration details of the endpoint. When specified, the authorization configuration MUST be a map of non-empty strings to non-empty strings. The configuration keys below MUST be used as defined. Additional, endpoint-specific configuration keys MAY be added.

  • Constraints:

    • OPTIONAL
    • MUST only be used for authorization configuration
    • MUST NOT be used for credential configuration

protocoloptions.authorization.type

  • Type: String

  • Description: The type of the authorization configuration. The value SHOULD be one of the following:

    • OAuth2: OAuth 2.0 authorization is used.
    • Plain: The client uses username with a plaintext password for authentication and authorization.
    • X509Cert: The client uses client certificate authentication and authorization.
    • APIKey: The client uses an API key for authentication and authorization.

  • Constraints:

    • OPTIONAL
    • MUST be a non-empty string if used

protocoloptions.authorization.resourceuri

  • Type: URI

  • Description: The URI of the resource for which the authorization is requested. The format of the URI depends on the authorization type.

  • Constraints:

    • OPTIONAL
    • MUST be a non-empty URI if used

protocoloptions.authorization.authorityuri

  • Type: URI

  • Description: The URI of the authorization authority from which the authorization is requested. The format of the URI depends on the authorization type.

  • Constraints:

    • OPTIONAL
    • MUST be a non-empty URI if used

protocoloptions.authorization.grant_types

  • Type: Array of Strings

  • Description: The supported authorization grant types. The value SHOULD be a list of strings.

  • Constraints:

    • OPTIONAL
    • MUST be a non-empty array if used

protocoloptions.deployed

  • Type: Boolean
  • Description: If true, the endpoint metadata represents a public, live endpoint that is available for communication and a strict validator MAY test the liveness of the endpoint.
  • Constraints:
    • OPTIONAL.
    • When not specified, the default value is MUST be false.

protocoloptions.options

  • Type: Map
  • Description: Additional configuration options for the endpoint. The configuration options are protocol specific and described in the protocol options section below.
  • Constraints:
    • OPTIONAL
    • When specified, MUST be a map of non-empty strings to ANY type values.
    • If protocoloptions.protocol is a well-known protocol, the options MUST be compliant with the protocol's options.

messagegroups

The messagegroups attribute is an array of URI-references to message definition groups. The messagegroups attribute is used to reference message definition groups that are not inlined in the endpoint definition.

Example:

{
  "protocol": "HTTP/1.1",
  "protocoloptions": {
    "method": "POST"
  },
  "messagegroups": [
    "https://example.com/registry/messagegroups/mygroup"
  ]
}

messages

Endpoints are supersets of message definition groups and MAY contain inlined messages. See Message Definitions.

Example:

{
  "protocol": "HTTP/1.1",
  "protocoloptions": {
    "method": "POST"
  },

  "messagesurl": "...",
  "messagescount": 1,
  "messages": {
    "myevent": {
      "envelope": "CloudEvents/1.0",
      "envelopemetadata": {
        "attributes": {
          "type": {
            "value": "myevent"
          }
        }
      }
    }
  }
}

When this specification, and the message specification, are used with specifications such as CloudEvents, where a semantically unique identifier is used in a runtime message (e.g. CloudEvent's type attribute), it is STRONGLY RECOMMENDED that the messageid values of the message definitions for an Endpoint match that unique identifier and therefore be unique across all messages within the messages collection and the messages referenced by the messagegroups attribute. This will allow for an easily "lookup" from an incoming runtime message to it's related message definition.

However, there are times when this is not possible. For example, take the case where an Endpoint might have the same semantic message defined twice, once for a JSON serialization and once for an XML serialization. Using the same messageid value is not possible (even though the CloudEvent type attribute would be the same for both runtime messages), so one (or both) message definition's messageid values might not match the runtime message's type value. In those cases, finding the appropriate message definition will need to be done via examination of some other metadata - such as the message's envelopemetadata.type value along with its envelopeoptions.format value. These details are of scope for this specification to define and are left as an implementation detail.

Implementations MAY choose to generate an error if it detects duplicate messageid values across the messages collection message definitions and the messagegroups referenced message definitions, if that is the desired constraints for their users.

Protocol Options

The following protocol options (protocoloptions.options) are defined for the respective protocols. All of these are OPTIONAL.

HTTP options

The endpoint URIs for "HTTP" endpoints MUST be valid HTTP URIs using the "http" or "https" scheme.

The following options are defined for HTTP:

  • method: The HTTP method to use for the endpoint.
    • When not specified the default value MUST be POST.
    • The value MUST be a valid HTTP method name.
  • headers: An array of HTTP headers to use for the endpoint. HTTP allows for duplicate headers. The objects in the array have the following attributes:
    • name: The name of the HTTP header. The value MUST be a non-empty string.
    • value: The value of the HTTP header. The value MUST be a non-empty string.
  • query: A map of HTTP query parameters to use for the endpoint. The value MUST be a map of non-empty strings to non-empty strings.

The values of all query and headers MAY contain placeholders using the RFC6570 Level 1 URI Template syntax. When the same placeholder is used in multiple properties, the value of the placeholder is assumed to be identical.

Example:

{
  "protocol": "HTTP/1.1",
  "protocoloptions": {
    "method": "POST",
    "headers": [
      {
        "name": "Content-Type",
        "value": "application/json"
      }
    ],
    "query": {
      "operation": "send"
    }
  }
}

AMQP options

The endpoint URIs for "AMQP" endpoints MUST be valid AMQP URIs using the "amqp" or "amqps" scheme. If the path portion of the URI is present, it MUST be a valid AMQP node name.

The following options are defined for AMQP endpoints.

  • node: The name of the AMQP node (a queue or topic or some addressable entity) to use for the endpoint.
    • When specified, the value overrides the path portion of the Endpoint URI.
  • durable: If true, the AMQP durable flag is set on transfers.
    • When not specified, the default value MUST be false.
    • This option only applies to usage:producer endpoints.
  • linkproperties: A map of AMQP link properties to use for the endpoint.
    • The value MUST be a map of non-empty strings to non-empty strings.
  • connection-properties: A map of AMQP connection properties to use for the endpoint.
    • The value MUST be a map of non-empty strings to non-empty strings.
  • distributionmode: Either move or copy.
    • When not specified, the default value MUST be move.
    • The distribution mode is AMQP's way of expressing whether a receiver operates on copies of messages (it's a topic subscriber) or whether it moves messages from the queue (it's a queue consumer). This option only applies to usage:consumer endpoints.

The values of all linkproperties and connection-properties MAY contain placeholders using the RFC6570 Level 1 URI Template syntax. When the same placeholder is used in multiple properties, the value of the placeholder is assumed to be identical.

Example:

{
  "usage": "producer",
  "protocol": "AMQP/1.0",
  "protocoloptions": {
    "node": "myqueue",
    "durable": true,
    "linkproperties": {
      "mylinkproperty": "mylinkpropertyvalue"
    },
    "connection-properties": {
      "my-connection-property": "my-connection-property-value"
    },
    "distributionmode": "move"
  }
}

MQTT options

The endpoint URIs for "MQTT" endpoints MUST be valid MQTT URIs using the (informal) "mqtt" or "mqtts" scheme. If the path portion of the URI is present, it MUST be a valid MQTT topic name. The informal schemes "tcp" (plain TCP/1883), "ssl" (TLS TCP/8883), and "wss" (Websockets/443) MAY also be used, but MUST NOT have a path.

The following options are defined for MQTT endpoints.

  • topic: The MQTT topic to use for the endpoint.
    • When specified, the value overrides the path portion of the Endpoint URI.
    • The value MAY contain placeholders using the RFC6570 Level 1 URI Template syntax.
  • qos: The MQTT Quality of Service (QoS) level to use for the endpoint.
    • The value MUST be an integer between 0 and 2.
    • When not specified, the default value MUST be 0.
    • The value is overidden by the qos property of the MQTT message format.
  • retain: If true, the MQTT retain flag is set on transfers.
    • When not specified, the default value is false.
    • The value is overidden by the retain property of the MQTT message format. This option only applies to usage:producer endpoints.
  • cleansession: If true, the MQTT cleansession flag is set on connections.
    • When not specified, the default value MUST be true.
  • willtopic: The MQTT willtopic to use for the endpoint.
    • The value MUST be a non-empty string.
    • The value MAY contain placeholders using the RFC6570 Level 1 URI Template syntax.
  • willmessage: This is URI and/or JSON Pointer that refers to the MQTT willmessage to use for the endpoint.

Example:

{
  "usage": "producer",
  "protocol": "MQTT/5.0",
  "protocoloptions": {
    "topic": "mytopic",
    "qos": 1,
    "retain": false,
    "cleansession": false,
    "willtopic": "mytopic",
    "willmessage": "#/messagegroups/mygroup/messages/mywillmessage"
  }
}

KAFKA options

The endpoint URIs for "Kafka" endpoints MUST be valid Kafka bootstrap server addresses. The scheme follows Kafka configuration usage, e.g. SSL://{host}:{port} or PLAINTEXT://{host}:{port}.

The following options are defined for Kafka endpoints.

  • topic: The Kafka topic to use for the endpoint.
    • When specified, the value MUST be a non-empty string.
    • The value MAY contain placeholders using the RFC6570 Level 1 URI Template syntax.
  • acks: The Kafka acks setting to use for the endpoint.
    • The value MUST be an integer between -1 and 1.
    • When not specified, the default value MUST be 1.
    • This option only applies to usage:producer endpoints.
  • key: The fixed Kafka key to use for this endpoint.
    • When specified, the value MUST be a non-empty string.
    • This option only applies to usage:producer endpoints.
    • The value MAY contain placeholders using the RFC6570 Level 1 URI Template syntax.
  • partition: The fixed Kafka partition to use for this endpoint.
    • When specified, the value MUST be an integer.
    • This option only applies to usage:producer endpoints.
  • consumergroup: The Kafka consumer group to use for this endpoint.
    • When specified, the value MUST be a non-empty string.
    • This option only applies to usage:consumer endpoints.
    • The value MAY contain placeholders using the RFC6570 Level 1 URI Template syntax.

Example:

{
  "usage": "producer",
  "protocol": "Kafka/2.0",
  "protocoloptions": {
    "topic": "mytopic",
    "acks": 1,
    "key": "mykey",
  }
}

NATS options

The endpoint URIs for "NATS" endpoints MUST be valid NATS URIs. The scheme MUST be "nats" or "tls" or "ws" and the URI MUST include a port number, e.g. nats://{host}:{port} or tls://{host}:{port}.

The following options are defined for NATS endpoints.

  • subject: The NATS subject to use.
    • The value MAY contain placeholders using the RFC6570 Level 1 URI Template syntax.

Example:

{
  "usage": "producer",
  "protocol": "NATS/1.0.0",
  "protocoloptions": {
    "subject": "mysubject"
  }
}

References