Event Framework

The purpose of the Event Framework is to provide a standard unified architecture to capture all Mojaloop events.

Disclaimer: This is experimental and is being implemented as a PoC. As such the design may change based on the evolution of the PoC's implementation, and any lessons learned.

1. Requirements

  • Events will be produced by utilising a standard common library that will publish events to a sidecar component utilising a light-weight highly performant protocol (e.g. gRPC).
  • Sidecar module will publish events to a singular Kafka topic that will allow for multiple handlers to consume and process the events as required.
  • Kafka partitions will be determined by the event-type (e.g. log, audit, trace, errors etc).
  • Each Mojaloop component will have its own tightly coupled Sidecar.
  • Event messages will be produced to Kafka using the Trace-Id as the message key. This will ensure that all the messages part of the same trace (transaction) are stored in the same partition in order.

2. Architecture

2.1 Overview

Event Framework Architecture

2.2 Micro Service Pods

Pod Architecture

2.3 Event Flow

Tracing Architecture

3. Event Envelope Model

3.1 JSON Example

{
    "from": "noresponsepayeefsp",
    "to": "payerfsp",
    "id": "aa398930-f210-4dcd-8af0-7c769cea1660",
    "content": {
        "headers": {
            "content-type": "application/vnd.interoperability.transfers+json;version=1.0",
            "date": "2019-05-28T16:34:41.000Z",
            "fspiop-source": "noresponsepayeefsp",
            "fspiop-destination": "payerfsp"
        },
        "payload": "data:application/vnd.interoperability.transfers+json;version=1.0;base64,ewogICJmdWxmaWxtZW50IjogIlVObEo5OGhaVFlfZHN3MGNBcXc0aV9VTjN2NHV0dDdDWkZCNHlmTGJWRkEiLAogICJjb21wbGV0ZWRUaW1lc3RhbXAiOiAiMjAxOS0wNS0yOVQyMzoxODozMi44NTZaIiwKICAidHJhbnNmZXJTdGF0ZSI6ICJDT01NSVRURUQiCn0"
    },
    "type": "application/json",
    "metadata": {
        "event": {
            "id": "3920382d-f78c-4023-adf9-0d7a4a2a3a2f",
            "type": "trace",
            "action": "span",
            "createdAt": "2019-05-29T23:18:32.935Z",
            "state": {
                "status": "success",
                "code": 0,
                "description": "action successful"
            },
            "responseTo": "1a396c07-47ab-4d68-a7a0-7a1ea36f0012"
        },
        "trace": {
            "service": "central-ledger-prepare-handler",
            "traceId": "bbd7b2c7-3978-408e-ae2e-a13012c47739",
            "parentSpanId": "4e3ce424-d611-417b-a7b3-44ba9bbc5840",
            "spanId": "efeb5c22-689b-4d04-ac5a-2aa9cd0a7e87",
            "startTimestamp": "2015-08-29T11:22:09.815479Z",
            "finishTimestamp": "2015-08-29T11:22:09.815479Z",
            "tags": {
              "transctionId": "659ee338-c8f8-4c06-8aff-944e6c5cd694",
              "transctionType": "transfer",
              "parentEventType": "bulk-prepare",
              "parentEventAction": "prepare"
            }
        }
    }
}

3.2 Schema Definition

3.2.1 Object Definition: EventMessage

Name Type Mandatory (Y/N) Description Example
id string Y The id references the related message.
from string N If the value is not present in the destination, it means that the notification was generated by the connected node (server).
to string Y Mandatory for the sender and optional in the destination. The sender can ommit the value of the domain.
pp string N Optional for the sender, when is considered the identity of the session. Is mandatory in the destination if the identity of the originator is different of the identity of the from property.
metadata object <MessageMetadata> N The sender should avoid to use this property to transport any kind of content-related information, but merely data relevant to the context of the communication. Consider to define a new content type if there's a need to include more content information into the message.
type string Y MIME declaration of the content type of the message.
content object \ Y The representation of the content.
3.2.1.1 Object Definition: MessageMetadata
Name Type Mandatory (Y/N) Description Example
event object <EventMetadata> Y Event information.
trace object <EventTraceMetaData> Y Trace information.
3.2.1.2 Object Definition: EventMetadata
Name Type Mandatory (Y/N) Description Example
id string Y Generated UUIDv4 representing the event. 3920382d-f78c-4023-adf9-0d7a4a2a3a2f
type enum <EventType> Y Type of event. [log, audit, error trace]
action enum <LogEventAction, AuditEventAction, TraceEventAction, NullEventAction> Y Type of action. [ start, end ]
createdAt timestamp Y ISO Timestamp. 2019-05-29T23:18:32.935Z
responseTo string N UUIDv4 id link to the previous parent event. 2019-05-29T23:18:32.935Z
state object <EventStateMetadata> Y Object describing the state.
3.2.1.3 Object Definition: EventStateMetadata
Name Type Mandatory (Y/N) Description Example
status enum <EventStatusType> Y The id references the related message. success
code number N The error code as per Mojaloop specification. 2000
description string N Description for the status. Normally used to include an description for an error. Generic server error to be used in order not to disclose information that may be considered private.
3.2.1.4 Object Definition: EventTraceMetaData
Name Type Mandatory (Y/N) Description Example
service string Y Name of service producing trace central-ledger-prepare-handler
traceId 32HEXDIGLC Y The end-to-end transaction identifier. 664314d5b207d3ba722c6c0fdcd44c61
spanId 16HEXDIGLC Y Id for a processing leg identifier for a component or function. 81fa25e8d66d2e88
parentSpanId 16HEXDIGLC N The id references the related message. e457b5a2e4d86bd1
sampled number N Indicator if event message should be included in the trace 1. If excluded it will be left the consumer to decide on sampling. 1
flags number N Indicator if event message should be included in the trace flow. ( Debug 1 - this will override the sampled value ) 0
startTimestamp datetime N ISO 8601 with the following format yyyy-MM-dd'T'HH:mm:ss.SSSSSSz. If not included the current timestamp will be taken. Represents the start timestamp of a span. 2015-08-29T11:22:09.815479Z
finishTimestamp datetime N ISO 8601 with the following format yyyy-MM-dd'T'HH:mm:ss.SSSSSSz. If not included the current timestamp will be taken. Represents the finish timestamp of a span 2015-08-29T11:22:09.815479Z
tags object <EventTraceMetaDataTags> Y The id references the related message. success

Note: HEXDIGLC = DIGIT / "a" / "b" / "c" / "d" / "e" / "f" ; lower case hex character. Ref: WC3 standard for trace-context.

3.2.1.5 Object Definition: EventTraceMetaDataTags
Name Type Mandatory (Y/N) Description Example
transactionId string N Transaction Id representing either a transfer, quote, etc 659ee338-c8f8-4c06-8aff-944e6c5cd694
transactionType string N The transaction type represented by the transactionId. E.g. (transfer, quote, etc) transfer
parentEventType string N The event-type of the parent Span. bulk-prepare
parentEventAction string N The event-action of the parent Span. prepare
<string> string N Arbitary Key-value pair for additional meta-data to be added to the trace information. n/a
3.2.1.6 Enum: EventStatusType
Enum Description
success Event was processed successfully
fail Event was processed with a failure or error
3.2.1.7 Enum: EventType
Enum Description
log Event representing a general log entry.
audit Event to be signed and persisted into the audit store.
trace Event containing trace context information to be persisted into the tracing store.
3.2.1.8 Enum: LogEventAction
Enum Description
info Event representing an info level log entry.
debug Event representing a debug level log entry.
error Event representing an error level log entry.
verbose Event representing a verbose level log entry.
warning Event representing a warning level log entry.
performance Event representing a performance level log entry.
3.2.1.9 Enum: AuditEventAction
Enum Description
default Standard audit action.
start Audit action to represent the start of a process.
finish Audit action to represent the end of a process.
ingress Audit action to capture ingress activity.
egress Audit action to capture egress activity.
3.2.1.10 Enum: TraceEventAction
Enum Description
span Event action representing a span of a trace.

4. Tracing Design

4.1 HTTP Transports

Below find the current proposed standard HTTP Transport headers for tracing.

Mojaloop has yet to standardise on either standard, or if it will possible support both.

4.1.1 WC3 Http Headers

Refer to the following publication for more information: https://w3c.github.io/trace-context/

Header Description Example
traceparent Dash delimited string of tracing information: \-\-\-\ 00-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7-00
tracestate Comma delimited vendor specific format captured as follows: \=\ congo=t61rcWkgMzE,rojo=00f067aa0ba902b7

Note: Before this specification was written, some tracers propagated X-B3-Sampled as true or false as opposed to 1 or 0. While you shouldn't encode X-B3-Sampled as true or false, a lenient implementation may accept them.

4.1.2 B3 HTTP Headers

Refer to the following publication for more information: https://github.com/apache/incubator-zipkin-b3-propagation

Header Description Example
X-B3-TraceId Encoded as 32 or 16 lower-hex characters. a 128-bit TraceId header might look like: X-B3-TraceId: 463ac35c9f6413ad48485a3953bb6124. Unless propagating only the Sampling State, the X-B3-TraceId header is required.
X-B3-SpanId Encoded as 16 lower-hex characters. a SpanId header might look like: X-B3-SpanId: a2fb4a1d1a96d312. Unless propagating only the Sampling State, the X-B3-SpanId header is required.
X-B3-ParentSpanId header may be present on a child span and must be absent on the root span. It is encoded as 16 lower-hex characters. A ParentSpanId header might look like: X-B3-ParentSpanId: 0020000000000001
X-B3-Sampled An accept sampling decision is encoded as 1 and a deny as 0. Absent means defer the decision to the receiver of this header. A Sampled header might look like: X-B3-Sampled: 1.
X-B3-Flags Debug is encoded as 1. Debug implies an accept decision, so don't also send the X-B3-Sampled header.

4.2 Kafka Transports

Refer to Event Envelope Model section. This defines the message that will be sent through the Kafka transport.

Alternatively the tracing context could be stored in Kafka headers which are only supports v0.11 or later. Note that this would break support for older versions of Kafka.

4.3 Known limitations

  • Transfer tracing would be limited to each of the transfer legs (i.e. Prepare and Fulfil) as a result of the Mojaloop API specification not catering for tracing information. The trace information will be send as part of the callbacks by the Switch, but the FSPs will not be required to respond appropriately with a reciprocal trace headers.

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