I have 5 instances of account microservice which transfers the money from account A to account B and then updates the data in the Postgres database. My problem is
A user sent five requests to the account service and all of my microservices are working in parallel each request went to all 5 services way but now the user doesn't have enough balance in the account and I am already checking if the user is having enough balance or not.
but after 2 requests user doesn't have enough balance so I am in confusion how to check this and implement data consistency first before the request goes to another instance of the same microservice.
I would love to have suggestions and other approaches also
It's hard problem to solve. You can make load balancer use sticky sessions so that single user requests always go to single instance. Either way, you need to make sure db locking is implemented so that at any time only one instance can update one row in a application consistent manner.