使用微服务和Spring Boot进行分布式事务

Question

currently i'm working on migrating a monolith app into microservices and the first issue i encountered is the famous distributed transactions problem.

i have a micro-service called authentication microservice having as a mission to authenticate users using Oauth2.

my problem is as follows :

the front-end is filling a form and sending a lot of data, some of it belong to the employee microservice and the other to the authentification service

so when i receive this data i must add at once a user and an employee. imagine now that the user was added but the employee not due to some sort of failure ? or even worse imagine when i'm deleting a user and the employee won't get deleted ?

so you may have in mind the 2PC or saga pattern, i invested 2 days reading and weighing the possibilities of using those solutions but it complicates things and i think that my problem is not worth it.

i posted the question in order to seek any new ideas or maybe there's some new technology i'm missing.

thank you

Answer 1

Adding a user doesn't need to be the job of authentication service. Insert both the employee and the user in the same service, and notify the auth service of the new user. (using one of many events/messaging systems)

Answer 2

There are in general two ways to achieving the same:

1. SAGA Pattern - You read it
2. You make transaction in one service , then another service listen to the event and perform update. Like on user removal , generate a event UserRemoved and Employee service listen to it and remove employee.

This is very important to understand in microservices:

Sometimes the api that you expose lets say create employee, it should create the user and employee both and return employee id and user id at the same time so these things could not be handled in any async transaction.

For these type of things we need to make system to auto correct such inconsistencies. For eg:

Lets say in CreateEmployee , first user id created the employee was not created because of some error, then again if somebody create a employee with same username what should id do. In this case if create employee handle such case that if already a user exists for that check whether employee also exists if not create employee and return.

There will be more such cases, so in microservices system should be auto correctable and eventual consistent. Trying everyting completely consistent everytime is not the right goal.