What is API

It’s like a humans conversation interface, but for the digital world.

At my previous company, we were talking about few Java developers that they have a “heavy interface” -> meaning “they are not most communicative, and close to a cave man”

Do you like when people call you Mr/Mrs/Miss/Sir?
What is your pronoun?
Do you care about your titles, should we say doctor or professor
Are you in the mood for a talk?
Do you like to start with small talk?

Wouldn’t it be nice to have it documented and publicly available? Oh wait -> Solid Project

Sync vs Async

What is a Protocol

Good real-life example is the dyplomatic protocol

New mission establishment
Credentials handover
Appointing new representatives

Example protocol implementation is the United Nations manual of protocol.

On technical side: It is a set of rules that describe how information is transmited.

HTTP protocol on example of AsyncAPI website :

Specifications

HTTP protocol:
- OpenAPI for REST API (although 3.1 no longer mentions it)
- GraphQL
Async-related protocols:

Event Driven Architecture (EDA)

Q: Why do you do event-driven API, is REST API not enough?

A1: Because I want to know what is happening in real-time without asking for an update constantly.

A2: When you send a message, and definitely do not expect a response.

there are many other patterns: Messaging Patterns

EDA is pretty old

Just look at the browser and mouseover event:

Microservices brought event-driven into renesance. Serverless puts it to the moon.

EDA protocols

amqp, http, ibmmq, jms, kafka, anypointmq, mqtt, solace, stomp, websocket, mercure

EDA Docs

Most complex to document because of different protocols
Not widely visible as REST API
- Programmableweb - 24,471 (Async APIs around 170)
- RapidAPI - Thousands!
- APIs Guru - 2,529 OpenAPI examples!
APITracker - 7 AsyncAPI examples…
REMEMBER: spec is not all you need

EDA Setup - Simplified

These two perspectives cause some headache in AsyncAPI

Clients & Server

  graph TD
    server1[Server -> ws://flypoland.pl/travel/status]
    user1[Client -> Browser]
    user1 --> server1
    user2[Client -> Mobile]
    user2 --> server1

Producers, consumers and message broker in the middle -> fire and forget
Step 1

  graph TD
    NotificationSubscribeUI[Subscribe-Me-For-Flight-Status UI]
    NotificationSubscribeUI -- HTTP POST --> FlightSubscriberService

Step 2

  graph TD
    server1{mqtt://flypoland.pl:1883}
    NotificationSubscribeUI[Subscribe-Me-For-Flight-Status UI]
    NotificationSubscribeUI -- HTTP POST --> FlightSubscriberService
    FlightSubscriberService[Flight Subscriber Service]
    FlightSubscriberService -- flight/queue --> server1

Step 3

  graph TD
    server1{mqtt://flypoland.pl:1883}
    NotificationSubscribeUI[Subscribe-Me-For-Flight-Status UI]
    FlightMonitorService[Flight Monitor Service]
    NotificationSubscribeUI -- HTTP POST --> FlightSubscriberService
    FlightMonitorService -- flight/status --> server1
    FlightSubscriberService[Flight Subscriber Service]
    FlightSubscriberService -- flight/queue --> server1
    server1 -- flight/queue --> FlightMonitorService

Step 4

  graph TD
    server1{mqtt://flypoland.pl:1883}
    NotificationSubscribeUI[Subscribe-Me-For-Flight-Status UI]
    FlightMonitorService[Flight Monitor Service]
    NotificationSubscribeUI -- HTTP POST --> FlightSubscriberService
    FlightMonitorService -- flight/status --> server1
    FlightNotifierService[User Notifier Service]
    server1 -- flight/status --> FlightNotifierService
    FlightSubscriberService[Flight Subscriber Service]
    FlightSubscriberService -- flight/queue --> server1
    server1 -- flight/queue --> FlightMonitorService
    SMSService[External SMS Service]
    FlightNotifierService -- HTTP POST --> SMSService

Final

  graph TD
      NotificationSubscribeUI[Subscribe-Me-For-Flight-Status UI]
      NotificationSubscribeUI -- HTTP POST --> FlightSubscriberService
    subgraph EDA World
      FlightMonitorService[Flight Monitor Service]
      server1{mqtt://flypoland.pl:1883}
      FlightMonitorService -- flight/status --> server1
      FlightNotifierService[User Notifier Service]
      server1 -- flight/status --> FlightNotifierService
      FlightSubscriberService[Flight Subscriber Service]
      FlightSubscriberService -- flight/queue --> server1
      server1 -- flight/queue --> FlightMonitorService
    end
    SMSService[External SMS Service]
    FlightNotifierService -- HTTP POST --> SMSService