Netflix took 7 years to completely transform to microservices. The traditional approach that was followed was that developers contributed to their individual jars/wars which would go through the regular sprint iteration.
As can be seen above that there are issues with the velocity for delivery and reliability.
Any one change in one service it would reflect into the other services which was very difficult to handle. This caused too many bugs and single point database. Few years back the production database of netflix got corrupted and the users/customers saw the following message.
At netflix they want their services to isolate single point failures so here comes Hystrix. Hystrix is a latency and fault tolerance library designed to isolate points of access to remote systems, services and 3rd party libraries, stop cascading failure and enable resilience in complex distributed systems where failure is inevitable.
They test their system with fault injection test framework (FIT).