Part of John Thompson's Microservices course

For microservices to use JMS Messaging on localhost, Docker must be installed and localhost must be connected to an ActiveMQ Server

https://github.com/vromero/activemq-artemis-docker

defaults for this docker image - github.com/vromero/activemq-artemis

spring.artemis.user=artemis spring.artemis.password=simetraehcapa

Docker ActiveMQ

Beer Service is responsible for generating the Beer objects used in the application and stores that Beer object data in a database. Beer Order Service and Beer Inventory make calls to Beer Service to get information about the Beer objects.

Beer object example:

• UUID id = '026cc3c8-3a0c-4083-a05b-e908048c1b08'
• String beer_name = 'Pinball Porter'
• String beer_style = 'PORTER'
• Timestamp created_date = CURRENT_TIMESTAMP
• Timestamp last_modified_date = CURRENT_TIMESTAMP
• Integer min_on_hand = 12
• Integer quantity_to_brew = 200
• BigDecimal price = 12.95
• String upc = '0083783375213'
• Long version = 1

Default Port Mappings - For Single Host

Service Name	Port
Brewery Beer Service	8080
Brewery Beer Order Service	8081
Brewery Beer Inventory Service	8082

Micro Beer Order Service

Steps for Deconstruction into Microservices

1. Dependency Management

2. (Local) MySQL Configuration

3. JMS Messaging

4. JMS with Microservices

5. Spring State Machine

6. Using Sagas with Spring

7. Integration Testing Sagas

8. Compensating Transactions

9. Spring Cloud Gateway

10. Service Registration

11. Service Discovery

12. Circuit Breaker

• Refactoring Model to Common Package

  • Goal - refactor package structure in all 3 microservices to share a common 'Brewery' package for all the Java objects that are shared between the microservices

    • When microservices are working with identical objects between them, avoids a lot of headaches with conversions, object manipulations, etc.
    • much cleaner, safer, etc.

  • Model - Objects exposed to JSON

    • things that we will send out to the Client as JSON, changing them, and bring them back in to the back-end as JSON, convert to Java objects and perform business logic and database operations from there

  • Problem - In Spring, serialization / de-serialization expects same package / object name

    • Could address w/ additional Jackson configuration

  • Solution - Move model objects to package - 'com.kwgdev.brewery.model'

    • All services are related under the 'Brewery' set of services

  • Problem - Lombok Builders with parent classes problematic

    • Solution - flatten classes

• Notes on Agile Software Development Process

  • Agile Software Development is an iterative development process

    • Software is developed in small increments
    • Widely adopted by companies
      • Often poorly implemented!
    • Agile is a VERY large topic!

  • Companies that use Agile often use SCRUM

  • SCRUM is a process framework

    • Tasks are planned in a backlog
    • Tasks are planned into a "Sprint"

  • A Sprint is typically a 2-4 week period of work for 5 to 9 people

    • Length and team size are highly debated

  • At the end of a Sprint, a Retrospective is held

    • Purpose is to reflect and improve for next iteration

  • A Typical Sprint Retrospective Model

    • What worked well?

      • Planning Issues in GitHub
        • Allows better visibility of what source code was changed
      • Having CI Builds to catch problems
        • 3 failures detected

    • What could be improved?

      • Ideally should not have had 3 CI build failures
        • Testing is VERY light
      • Need better examples of Compensating Transactions

    • What will we commit to doing in the next Sprint?

      • Improve Test Coverage
        • Testing has not been a focus
        • Saga's clearly have a lot of moving parts!
          • Verify the Saga with Saga Integration Tests
        • Improve examples of Compensating Transactions

    • Scrum Team members make actionable commitments

      • Integration Tests

        • Unit Tests typically target a single class
        • Integration tests will test the interactions between components
        • In our microservice, we want to test:
          • Receiving a new order
          • Sending / Receiving JMS messages
          • Persistence
          • State Changes in the State Machine

      • Compensating Transactions

        • Problem - current 'non-happy' path events end in a terminal state
        • need example of compensating transactions
          • Non-happy path - call service to 'undo' action

• Deconstruction Process - 12/28/2020

  • Where We Are At

    • Beer Monolith has been broken down into 3 independent microservices
      • Beer Service, Beer Inventory and Beer Order Service
    • Each microservice is using its own in-memory database, its own repository
    • Setup inter-service communication for read operations
      • the Beer API is dependent on Beer Inventory to get inventory data
      • the Beer Order Service is dependent on Beer Service to get data about the Beer objects themselves (descriptions, properties, etc.)
      • So we can see how these services are starting to work together

  • What's Not Working

    • Order Allocation is not working
    • Beer 'Brewing" is not working
    • Monolith was using Spring Events and scheduled jobs for these features
      • Events and consumers of events is broken
    • The 3 services are using Maven, but there is a high degree of duplication in Maven POM files

  • Next Steps

    • Establish a Maven BOM (Bill of Materials) to reduce duplication in Maven POMs
      • Also - good technique for standardization and compliance across the enterprise
      • By making all subsystems and microservice POMs dependent on a BOM, don't have to go in and update each one every time some version is updated or patched
    • Setup MySQL for database - will help with trouble shooting, and configuration for target deployment
    • Transaction to JMS (Java Message Service) to publish events as messages
    • Build Saga's to coordinate microservice actions for events
      • ie Order Allocation

Docker ActiveMQ

5. Running the image

There are different methods to run a Docker image, from interactive Docker to Kubernetes and Docker Compose. This documentation will cover only Docker with an interactive terminal mode. You should refer to the appropriate documentation for more information around other execution methods.

To run ActiveMQ with AMQP, JMS and the web console open (if your are running 2.3.0 or later), run the following command:

MAC

docker run -it --rm
-p 8161:8161
-p 61616:61616
vromero/activemq-artemis

WINDOWS docker run -it --rm -p 8161:8161 -p 61616:61616 vromero/activemq-artemis

After a few seconds you'll see in the output a block similar to:

---

/ \ | | ___ __ __() _____
/ _ | _ \ __|/ _ \ / | |/ __/
/ ___ \ | / |/ / |/| | |_ \
// _| __|| |||/__ /
Apache ActiveMQ Artemis x.x.x

HH:mm:ss,SSS INFO [...] AMQ101000: Starting ActiveMQ Artemis Server

At this point you can open the web server port at 8161 and check the web console using the default username and password of artemis / simetraehcapa.