Monitoring system resources and microservices is becoming vital for realizing the original benefits of MSA. There are service and application monitoring tools. As most microservices are being containerized, container monitoring tools have gained prominence recently. There are even monitoring tools for Kubernetes, which has gained the top slot and spot as the container life cycle management platform. As this chapter has been specially prepared to explain everything about API gateways, it is logical to write about API gateway monitoring. API gateways are paramount and pertinent for the intended success of microservices in delivering a variety of functionalities. Every service request/response gets routed through them. The monitoring and measurement of the API's operation, performance, health condition, scalability, security, and log data are critical for meeting the agreed SLA and OLA parameters. The much-insisted health monitoring is done to make sure the gateway is up and running all the time. Monitoring is indispensable for ensuring service reliability and stability. The aspect of observability is vital for service availability, adaptability, and analytics. For minutely monitoring the health of systems, resource parameters such as processing power, memory capacity, and I/O rates (network and storage) are the main focus. The other important things to be precisely monitored and measured are the connectivity (network), security alerts, secure backups, recovery (data and disaster), and so on. Finally, logging data plays a very important role in supplying a lot of useful and usable information to the concerned in solidifying and shaping up the distinct goal of business continuity.  

The other important factor is nothing but the traffic monitoring. Gathering and deeply analyzing traffic data will enable the operations team to consider, contemplate, and carry out correct  measures in time, with all the clarity and confidence. The essential metrics to be faithfully considered include the total number of requests being sent out for an API for a period of time, the performance/throughput value, the number of successful and exception messages received, the number of blocked messages by API gateway, and so on. Also, request categorization is taken into consideration. This deeper and deft analysis helps to easily predict traffic situations with greater accuracy so that any kind of spike and surge can be taken care of without any kind of breakdown or slowdown.