A beginning guide to Vert.x, the main elements, and the main features, like Event Loop, Verticles, and Event Bus. Includes a link to a GitHub repository with samples.

1. Vert.x – Event Driven Non Blocking Reactive Toolkit
Brian S Paskin, Senior Application Architect, R&D Services, IBM Cloud Innovations Lab
6 April 2020
WebSphere Liberty Lunch and Learn

2. Introduction
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 Vert.x is an open source project by the Eclipse Foundation
 Is a reactive toolkit that can used as a serverless implementation or in an application
 Used for writing asynchronous network applications
 Supported under multiple Java based languages (polyglot)
– Java, Kotlin, JavaScript, Groovy, Ruby, Scala
 Has two programming methods, with or without Verticles (spelled that way)
 There are different libraries for databases, monitoring, logging, et cetera
 Non blocking and event driven that is scalable using an Event Bus
– Uses an Event Loop to process requests
– Event Bus to handle communications between Verticles
– Can span multiple JVMs and systems
 Can be used with Quarkus and GraalVM
 Requires Maven Shade to create a fat jar

3. Introduction
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4. Event Loop
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 Implementation of the multi Reactor design pattern
– Continuously checking for new events and pass it to the proper Handler
– Normal Reactor is single threaded, but Vert.x is multi-threaded
 Number of threads for the Event Loop depends on the number of processors
– Is equal to 2 * number of processors
– Not based on the number of Verticles deployed
– Threads are assigned in a round robin method for Verticles
 Verticles will always execute on the assigned thread
 Worker Verticles have their own thread pools
 The Context is passed to the Verticle from the Event Loop
– All Handlers in an Event Loop run using the same Context
– Each Context has its own error handler
– Maintains thread safety
 Never block the event loop

5. Event Loop, Contexts, and Verticles
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6. Verticles
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 A Verticle is a unit of deployment
 Assigned a Thread in an Event Loop
 Each Verticle has an isolated classloader and cannot share global state
 Verticles can be passed configuration information
 2 Different Types of Verticles
– Standard
– Workers
 A standard Verticle should be quick and a non blocking unit of work
 A worker Verticle is like a standard Verticle but using a different Thread pool
– Can call blocking code
– Used for limiting number of executions of code (ie. calling backend system)
 Can be run in high available mode
– Deploys new Verticle if it dies abruptly

7. Event Bus
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 The Event Bus is used for Verticles to communicate with each other by sending messages
– Single instance per Vert.x instance
– Asynchronous
 Can be used with Verticles in the same JVM or across multiple JVMs and systems
– Outside of a single JVM Hazelcast is used to transport messages
 Can be used to communicate with JavaScript
 Three types of messaging
– Publish and subscribe
– Point to point
– Request – response
 Failures in all or part of the Event Bus may lead to lost messages

8. Introduction
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9. Common Libraries Highlights
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 Core
– Deploy Verticles
– HTTP Server
– Basic Event Bus
– Logging
– JSON and Parser
– Datagrams
– Metrics
– High availability and failover
– Timer events
– Buffers
 Web
– Route requests to Handlers and sub routers
– Routing based on criteria (HTTP Method, MIME type, etc.)
– Authentication (OAuth, Basic)
– Serve web pages
– CORS
– Uploads
– Cookie Handling
– Form handling
– Virtual hosts
– SockJS support

10. Common Libraries Highlights
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 Configuration
– Multiple formats (JSON, Properties, YAML, HOCON, System Props, Environment Entries, etc.)
– Can read default configuration file or specify file
– Different configurations can be passed to different Verticles
 JDBC Client
 MongoDB Client
 SQL Common
– Used in conjunction of one of the other data access libraries
 Reactive
– Uses RxJava
 Circuit Breaks for Micro Services
 MQTT
 Kafka Client
 Mail Client

11. More information
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 Sample code on GitHub
 Libraries
 Build a starter application