Saga Pattern Realization With MicroProfile LRA

This project includes an example implementation of the Saga pattern using MicroProfile LRA. The example application represents a travel application that consists of three backend services: TravelService, HotelService and FlightService. For simplicity reasons, only the workflow for booking a trip has been implemented.

Start the Application

Run ./gradlew clean build
Execute docker-compose up

Requesting trip bookings is now possible. Either use curl commands, the provided TravelApplication.json insomnia file, which includes different trip booking requests, or access the Swagger UI of the different services:

Service	URL to Swagger UI
TravelService	http://localhost:8090/openapi/ui/
LRA Coordinator (included in TravelService)	http://localhost:8090/openapi/ui/
HotelService	http://localhost:8081/openapi/ui/
FlightService	http://localhost:8082/openapi/ui/

An example for such a request:

TravelRequest

{
    "duration":
    {
        "start":"2021-12-01",
        "end":"2021-12-12"
    },
    "start":
    {
        "country":"Scotland",
        "city":"Stirling"
    },
    "destination":
    {
        "country":"Sweden",
        "city":"Stockholm"
    },
    "travellerName": "Max Mustermann",
    "boardType":"breakfast",
    "customerId":"1"
}

To simulate a Saga that fails because no hotel or no flight is available, use one of the following Strings as destination country in the trip booking request:

"Provoke hotel failure"

"Provoke flight failure"

The services also provide a general health endpoint that shows information about the system whether it is up and running. These endpoints can be accessed via:

Service	URL to health endpoint
TravelService	http://localhost:8090/health
HotelService	http://localhost:8081/health
FlightService	http://localhost:8082/health

If you are on Windows or Mac, you sometimes have to replace localhost with the default IP of your docker machine (use docker-machine ip default to get this default IP).

Stop the Application

To stop the application and remove the created containers, execute the following command:

docker-compose down --remove-orphans

General Saga Characteristics

External Compensation Trigger

In order to start the compensation of a currently running Saga externally, the LRA coordinator offers an endpoint to trigger the compensation of a specific LRA. To achieve that, an empty PUT request has to be sent to the LRA coordinator at: http://localhost:8090/lrac/lra-coordinator/{lraId}/cancel

The TravelApplication.json insomnia file also includes this request within the ExternalCompensationTrigger directory.

Monitor the Application

Log Files

Each service provides a log that contains some information about it. The logs can be accessed using the name of the relevant container. The different logs can be accessed using the following commands:

Log of	Command to execute
TravelService	`docker logs travelservice_microProfile`
HotelService	`docker logs hotelservice_microProfile`
FlightService	`docker logs flightservice_microProfile`

By using the --follow supplement, it will be continued to stream the service's output to the console.

The logging level can be changed in the respective application.properties file.

Tracing

The services include the necessary gradle dependencies as well as the feature within the server.xml to enable distributed tracing with Zipkin or with Jaeger. If tracing with Jaeger is enabled, Zipkin will not work. Information on how to activate/deactivate the respective tracing technology is described in the following two subsections. The default is that Zipkin is activated and Jaeger deactivated. Here, the main difference between Zipkin and Jaeger is that only Zipkin also shows the traces for requests to the LRA Coordinator.

a) Zipkin

The Zipkin UI can be accessed via http://localhost:9411/zipkin/

The following shortly describes how to activate and deactivate tracing with Zipkin:

Activate Zipkin [default]: Go to the respective server.xml and uncomment the following line within the featureManager section
```
    <feature>usr:opentracingZipkin-0.33</feature>
```
The following line must also be uncommented within the server.xml:
```
    <opentracingZipkin host="${zipkin.host}" port="9411"/>
```
Additionally, the following line should be active within the respective build.gradle:
```
    compile "WASdev:sample.opentracing.zipkintracer:2.0.1@zip"
```
Additionally, make sure that the Zipkin service is active within the docker-compose.yml and that the following environment variable is set for each microservice:
```
    ZIPKIN_URI: zipkin
```
Deactivate Zipkin: Go to the respective server.xml and comment the following line out within the featureManager section
```
    <feature>usr:opentracingZipkin-0.33</feature>
```
Additionally, the following line must also be commented out within the server.xml:
```
    <opentracingZipkin host="${zipkin.host}" port="9411"/>
```

b) Jaeger

The Jaeger UI can be accessed via http://localhost:16686/

The following shortly describes how to activate and deactivate tracing with Jaeger:

Activate Jaeger: Go to the respective build.gradle files and activate within the dependencies section the following line:
```
  compile "io.jaegertracing:jaeger-client:1.6.0"
```
Additionally, make sure that the Jaeger service is active within the docker-compose.yml and that the following four environment variables are set and active for each microservice:
```
      JAEGER_AGENT_HOST: jaeger
      JAEGER_AGENT_PORT: 6831
      JAEGER_SAMPLER_TYPE: const
      JAEGER_SAMPLER_PARAM: 1
```
Deactivate Jaeger [default]: Go to the respective build.gradle files and comment out, within the dependencies section, the following line:
```
  compile "io.jaegertracing:jaeger-client:1.6.0"
```

Metrics

The individual microservices are publishing some metrics like the number of executed requests to a specific endpoint. Additionally, the LRA Coordinator publishes some metrics like the maximum duration time of closing an LRA. These metrics are also published by the TravelService since the TravelService includes the coordinator.

Service	URL to Swagger UI
TravelService	http://localhost:8090/metrics/
LRA Coordinator (included in TravelService)	http://localhost:8090/metrics/
HotelService	http://localhost:8081/metrics/
FlightService	http://localhost:8082/metrics/

Code Link

MicroProfile_Implementations/MicroProfile

Last update: 2022-02-15