tahniat-ashraf / vertx-async-to-sync

Consume an async api (with callback) from sync endpoint using vert.x

vertx-async-to-sync

Problem statement

Suppose we have two services - A and B.

In a trivial and everyday scenario, client makes request to A. A then does some operations and makes a rest call request to B. B does some operations of it's own and gets back with a response to A. A receives the response from B, does some operations and sends response back to the client.

What if the api provided by B is asynchronous in nature?

For problem purpose, let's now give B some defined characteristics-

1. Expects caller's callbackUrl in request body
2. Upon receiving request from caller, performs some basic validtions of the request body.
3. If the validation is successful, returns an acknowledgement response to the caller
4. After that, it does the actual job in asynchronous manner
5. Upon completion of the job, it sends the response in caller's callbackUrl (passed during original request)

This complicates our previously mentioned trivial scenario. A will now only get the acknowledgement response in the initial rest call to B. It will receive the actual callback response in it's callbackUrl.

If we are to keep the behavior / user journey unchanged in client side (makes request to A and expects actual response) - this requires a level of engineering.

This project aims to solve the problem statement using vert.x and it's built in event bus.

Summary of Approach

Note: vertx-consumer-sync module replicates A, vertx-producer-async module replicates B

To add certain level of complexity, B service provides CRUD service based APIs on the entity class POST. MongoDB has been used as the underlying database. When client makes request to A, A then makes request to B. Upon making a request to B, A starts a timer of 29 seconds, within which both the acknowledgement and callback must reach A.

• In a happy scenario - B receives request from A, validates the request. Validation is successful. B sends acknowledgement response back to A. It then performs some MongoDB operation and sends the response in A's callbackUrl. This whole process is completed with 29 second. A sends the final response back to client.
• Not so happy scenario (1) - B receives request from A, validates the request. Validation fails. Sends failure acknowledgement response back to A. A sends the final failure message back to client.
• Not so happy scenario (2) - B receives request from A, validates the request. Validation is successful. B sends acknowledgement response back to A. It then performs some MongoDB operations and sends the response in A's callbackUrl. The whole process exceeds the limit of 29 seconds. A sends timeout response back to client.

How to Run

Pre-requisites

1. Docker
2. Java 11

Steps

1. Open terminal. Start the docker containers. Write docker-compose up -d
2. Open terminal. Start verx-consumer-sync (service A)

cd vertx-consumer-sync
mvn clean package
java -jar target/*-fat.jar

3. Similarly, start vertx-producer-async (service B)

cd ../vertx-producer-async
mvn clean package
java -jar target/*-fat.jar

4. Open terminal. Insert 100 sample posts in our mongodb collection for test purpose (thanks to jsonplaceholder)

curl --location --request POST 'localhost:9081/addBulkPosts'

Testing

CURL Commands

• Find all Posts

curl --location --request GET 'localhost:9080/posts'

• Get Post by id

curl --location --request GET 'localhost:9080/posts/1'

• Create new Post

curl --location --request POST 'localhost:9080/posts' \
--header 'Content-Type: application/json' \
--data-raw '{
    "userId": 1,
    "id": 101,
    "title": "Lorem Ipsum Title",
    "body": "Lorem Ipsum Body"
}'

• Update Post

curl --location --request PUT 'localhost:9080/posts' \
--header 'Content-Type: application/json' \
--data-raw '{
    "userId": 1,
    "id": 101,
    "title": "Lorem Ipsum Title - NEW",
    "body": "Lorem Ipsum Body - NEW"
}'

• Delete Post by id

curl --location --request DELETE 'localhost:9080/posts/101'