This book contains a number of specific terms that you might not have come across before, and here is a brief glossary to help you while reading this book:

• Ingress gateway: In Kubernetes, an ingress is an object that allows external access to internal microservices. An ingress is a collection of rules to route external traffic to services inside the Kubernetes cluster. In Istio, the ingress gateway sits at the edge of the cluster and allows the creation of multiple ingress gateways to configure access to the cluster.
• Egress gateway: The egress gateway is a feature of Istio that allows external access to the microservices running inside a Kubernetes cluster. This gateway also sits on the edge of the service mesh.
• Polyglot programming: This is the practice of writing code in multiple languages for services. For example, we can write different microservices in different languages, such as Go, Java, Ruby, and Python, and yet they can still communicate with one another.
• A/B testing: This is testing between two versions (A and B) of a microservice while both are in production.
• Canary release: This entails moving faster for cloud-native applications. Canary release is about a new version of a microservice available to a small subset of users in a production environment along with the old version. Once the new version can be used with confidence, the old version can be taken out of service without any ensuing disruption. 
• Circuit breaker: A failure of communication between microservices may occur due to latency or faults. The circuit breaker breaks the connection between microservices following the detection of latency/faults. The incoming traffic then reroutes to other microservices to avoid partial or cascading failures. The circuit breaker helps to attain load balancing and to prevent the continual overloading of a particular system.