CloudEvents¶

CloudEvents is a specification for describing event data in a common way. We want to support this vendor-neutral specification.

Currently we depend on the CloudEvents specification v0.2.

Attributes¶

Context Attributes (REQUIRED):

type – cloud event definition
specversion – cloud event definition
source – cloud event definition
id – change id if message was changed significantly (data translation, ignoring addition only changes) if id changed add previous message id as createdFrom to message (overwriting previous createdFrom)

Context Attributes (OPTIONAL):

time – cloud event definition Change to current time if id changed
schemaurl – cloud event definition
contenttype – cloud event definition, contenttype + schemaurl define the complete message format
subject - definition of CloudEvents spec v0.3: Identifying the subject of the event in context metadata (opposed to only in the data payload) is particularly helpful in generic subscription filtering scenarios where middleware is unable to interpret the data content. In the above example, the subscriber might only be interested in blobs with names ending with ‘.jpg’ or ‘.jpeg’ and the subject attribute allows for constructing a simple and efficient string-suffix filter for that subset of events.
createdfrom – id of the message this message was directly created from
correlationid – always keep if set, even in answers to this message (often the id of first message in a createdfrom chain)
route – list of topics and functions the message was sent to (updated by sender), keep until destination of message The entrys are json objects with a type, id and timestamp attribute. The type is either "topic" or "faas-function". The id is either the topic name or the function id. The timestamp is the time when the entry was added (before sending the message to the topic or function).
routingslip – stack of topics the message should be routed to (last entry is the next destination) The stack is represented as a json list. The entrys are lists of topic names (["topic1", "topic2"]). The message is routed to ALL topics in the same list simultaneously.
istestmessage – boolean flag for test messages
filteroutbeforetopic – only applies to test messages. Message should never be sent to specified topic but instead be routed to the collection topic for test messages to be inspected by a user.
iserrormessage – boolean flag for error messages The message that caused this error should be added as data in the error message. The id of the message causing the error should be used as the createdfrom value in the error message.
errormessage – string containing the (short) error message
errortrace – string containing additional information about the error. This could be a full stacktrace, part of a log or even json containing structured information about the error.
expirydate – for messages that should be considered stale after this date. Stale messages should not be consumed. They can be routed to the error message collection topic or a special topic for stale messages only.
sequenceid – message id for messages split into a sequence of messages
sequencenumber – the position of this message in the sequence as an Integer. The sequence MUST start with a value of 1 increase by 1 for each subsequent value.
sequencesize – the number of messages in the sequence as an Integer (only if known, this attribute is not required)
returntopic – the return address for replies to this message (implementation details to be decided by the user)
dataref – cloud event v0.3 extension
partitionkey – used as key when sending a kafka message. cloud event v0.3 extension

Data Attribute:

data – cloud event definition

Examples¶

Minimal:

{
    "specversion" : "0.2",
    "type" : "io.github.ust.mico.result",
    "source" : "/router",
    "id" : "A234-1234-1234",
    "time" : "2019-05-08T17:31:00Z",
    "contenttype" : "application/json",
    "data" : {
        "key" : "value"
    }
}

With routing fields:

{
    "specversion" : "0.2",
    "type" : "io.github.ust.mico.result",
    "source" : "/router",
    "id" : "A234-1234-1234",
    "correlationid": "A234-1234-1234",
    "time" : "2019-05-08T17:31:00Z",
    "contenttype" : "application/json",
    "data" : {
        "key" : "value"
    },
    "route": [
        {
            "type": "topic",
            "id": "first-topic",
            "timestamp": "2019-05-08T17:31:30Z"
        },
        {
            "type": "faas-function",
            "id": "xmlToJson",
            "timestamp": "2019-05-08T17:31:55Z"
        }
    ],
    "routingslip": [
        ["final-destination"],
        ["filter", "debug-topic"],
        ["next-destination"]
    ]
}