An e-commerce website has a huge user base. If all users were upgraded immediately, a major bug would have a significant impact on all users. To minimize this impact, during the version upgrade…

An e-commerce website has a huge user base. If all users were upgraded immediately, a major bug would have a significant impact on all users. To minimize this impact, during the version upgrade, some users were assigned to the higher-level version while others continued to use the lower-level version. Once the higher-level version stabilized, all user traffic was gradually migrated to the higher-level version, achieving a smooth upgrade. Which of the following features of a microservices solution is used here?