In this chapter, we learned how containers communicate with each other. We also introduced how pod-to-pod communication works. A service is an abstraction that routes traffic to any of the pods underneath it if the label selectors match. We also learned how a service works with a pod using iptables. We also familiarized ourselves with how packet routes from external services to a pod using DNAT and un-DAT packets. In addition to this, we looked at new API objects such as ingress, which allows us to use the URL path to route to different services in the backend. In the end, another NetworkPolicy object was introduced. This provides a second layer of security, and acts as a software firewall rule. With the network policy, we can make certain pods communicate with certain other pods. For example, only data retrieval services can talk to the database container. In the last section, we got a glimpse at Istio, one of the popular implementations of service mesh. All of these things make Kubernetes more flexible, secure, robust, and powerful. 

Before this chapter, we covered the basic concepts of Kubernetes. In Chapter 7, Monitoring and Logging, we'll get a clearer understanding of what is happening inside your cluster by monitoring cluster metrics and analyzing applications and system logs for Kubernetes. Monitoring and logging tools are essential for every DevOps, which also plays an extremely important role in dynamic clusters such as Kubernetes. Consequently, we'll get an insight into the activities of the cluster, such as scheduling, deployment, scaling, and service discovery. Chapter 7, Monitoring and Logging, will help you to better understand the act of operating Kubernetes in the real world.