In the last decade, we saw a significant shift in how modern, internet-scale applications are being built. Cloud computing (infrastructure as a service) and containerization technologies (popularized by Docker) enabled a new breed of distributed system designs commonly referred to as microservices (and their next incarnation, FaaS). Successful companies like Twitter and Netflix have been able to leverage them to build highly scalable, efficient, and reliable systems, and to deliver more features faster to their customers.
While there is no official definition of microservices, a certain consensus has evolved over time in the industry. Martin Fowler, the author of many books on software design, argues that microservices architectures exhibit the following common characteristics [1]:
Componentization via (micro)services: The componentization of functionality in a complex application is achieved via services, or microservices, that are independent processes communicating over a network. The microservices are designed to provide fine-grained interfaces and to be small in size, autonomously developed, and independently deployable.
Smart endpoints and dumb pipes: The communications between services utilize technology-agnostic protocols such as HTTP and REST, as opposed to smart mechanisms like the Enterprise Service Bus (ESB).
Organized around business capabilities: Products not projects: the services are organized around business functions ("user profile service" or "fulfillment service"), rather than technologies. The development process treats the services as continuously evolving products rather than projects that are considered to be completed once delivered.
Decentralized governance: Allows different microservices to be implemented using different technology stacks.
Decentralized data management: Manifests in the decisions for both the conceptual data models and the data storage technologies being made independently between services.
Infrastructure automation: The services are built, released, and deployed with automated processes, utilizing automated testing, continuous integration, and continuous deployment.
Design for failure: The services are always expected to tolerate failures of their dependencies and either retry the requests or gracefully degrade their own functionality.
Evolutionary design: Individual components of a microservices architecture are expected to evolve independently, without forcing upgrades on the components that depend on them.
Because of the large number of microservices involved in building modern applications, rapid provisioning, rapid deployment via decentralized continuous delivery, strict DevOps practices, and holistic service monitoring are necessary to effectively develop, maintain, and operate such applications. The infrastructure requirements imposed by the microservices architectures spawned a whole new area of development of infrastructure platforms and tools for managing these complex cloud-native applications. In 2015, the Cloud Native Computing Foundation (CNCF) was created as a vendor-neutral home for many emerging open source projects in this area, such as Kubernetes, Prometheus, Linkerd, and so on, with a mission to "make cloud-native computing ubiquitous."
"Cloud native technologies empower organizations to build and run scalable applications in modern, dynamic environments such as public, private, and hybrid clouds. Containers, service meshes, microservices, immutable infrastructure, and declarative APIs exemplify this approach.
These techniques enable loosely coupled systems that are resilient, manageable, and observable. Combined with robust automation, they allow engineers to make high-impact changes frequently and predictably with minimal toil."
-- Cloud Native Computing Foundation Charter [2]
At the time of writing, the list of graduated and incubating projects at CNCF [3] contained 20 projects (Figure 1.1). They all have a single common theme: providing a platform for efficient deployment and operation of cloud-native applications. The observability tools occupy an arguably disproportionate (20 percent) number of slots:
CNCF sandbox projects, the third category not shown in Figure 1.1, include two more monitoring-related projects: OpenMetrics and Cortex. Why is observability in such high demand for cloud-native applications?
Figure 1.1: Graduated and incubating projects at CNCF as of January 2019. Project names and logos are registered trademarks of the Linux Foundation.