Microservices can be less stable than other options. While an individual microservice may be well-tested, perhaps in conjunction with some common microservices and programs, it’s virtually impossible to test every configuration of microservices. As you combine them, they may interact in unforeseen ways.

They can also be less secure. It’s not always easy to tell where microservices reside, which can make securing them a headache. And with different microservices interacting with each other, this gives hackers more opportunities to penetrate the system. Savvy DevOps teams are moving to a more granular security policy called microsegmentation to get around this problem — but the solution isn’t universal yet.

It can be difficult to make the transition. If a company has been producing and maintaining a monolithic application, it will take time and discipline to replace it with a microservices architecture — although many companies have successfully accomplished this, and found the investment worthwhile.

https://dzone.com/articles/microservices-benefits-and-challenges