An API gateway acts as a reverse proxy, sitting between client applications and the backend microservices. It provides a single entry point and hides the complexities of services in the backend. The gateway handles routing requests to the appropriate services, aggregating data from multiple services, and applying policies consistently across all microservices.

Key responsibilities

• Some key responsibilities handled by a microservices API gateway include:
• Routing - Forwards requests to the appropriate microservice based on URL, content, business rules
• Security - Applies authentication, access control, threat protection 
• Traffic control - Load balancing, caching, rate limiting, etc. 
• Orchestration - Service discovery, failure handling like retries and circuit breaking
• Observability - Logging, monitoring and tracing
• Transformation - Protocol translation, response formatting, etc.

By handling these cross-cutting concerns, an API gateway simplifies building individual microservices to focus on core business capabilities.

Microservices architecture delivers immense advantages for building complex, scalable applications. By breaking an application down into small, independent services focused on discrete capabilities, teams can develop, deploy and scale these services faster. Microservices also aid innovation by decentralizing decisions around technology selection, data ownership, and development lifecycles. However, this distributed approach also introduces significant challenges from both a technical and organizational perspective that API gateways are purpose-built to address.

The decentralized nature of microservices means there are many more moving parts to manage. Instead of a single application, development teams must now track dozens or hundreds of separate microservices. This explosion of services exponentially increases the complexity of dependencies, networking, deployment topologies, data flows, and failure domains to model and optimize.

Additionally, microservices teams tend to have higher degrees of organizational independence and move at different paces. However, their output still needs to harmonize collectively for a smooth end-user experience. Without careful coordination, poor visibility between teams can quickly lead to conflicts, technical debt, and solution sprawl.

API gateways create a structural paradigm to tame this complexity. They provide standardization and governance across all microservices regardless of the implementation technology. Gateways handle cross-cutting capabilities that would otherwise need duplication across services, such as security, traffic controls, and failure handling strategies. Instead of this logic existing in a fragmented way, gateways centralize it consistently.

Client applications can no longer rely on a single hostname or IP address to access essential application services. Microservices may deploy to ephemeral containers or serverless functions spread across multiple internal networks and cloud providers. However, callers should not have to lookup locations for each backend service through complex service discovery mechanisms.

API gateways solve this problem by providing a unified domain name to consolidate access to all internal microservices. Teams can migrate services to different regions, clouds, or containers without affecting the caller experience. The gateway handles routing to the appropriate location dynamically while presenting a single entry point.

Similarly, microservices built in different programming languages can each expose their own unique protocols. But requiring client apps to integrate varied APIs creates expensive coupling that hinders agility. Gateways placed in front of microservices can handle protocol translations such that callers only need to use a single standardized protocol like GraphQL or REST.

Microservices depend on extensive redundancy and efficient failover between service instances to meet availability expectations. However, developing sophisticated health checks, load balancing algorithms, cascading failovers, and retries across each service is operationally demanding.

API gateways provide these resiliency capabilities consistently across all microservices out of the box. Teams can focus on coding business logic rather than rebuilding foundational patterns. Gateways introducing a standards-based resiliency layer for the entire backend.

The expansive surface area of numerous microservices exposes far more internal assets to potential compromise. Attack vectors multiply as more ports open to integrate various services, protocols, and diagnostic tools. Unprotected traffic between microservices likewise increases threats from unauthorized access or injection attacks.

API gateways implement a key API security paradigm by funneling all inbound integration through a single intermediary. This consolidated entry point is easier to comprehensively fortify against protocol and application-level exploits using authentication, access controls, threat intelligence, and WAF capabilities. Gateways can also encrypt inter-service traffic flows to secure critical communication channels inside a microservice mesh.

Using an API gateway strategically positions organizations to realize the transformational potential of microservices. Gateways fill a profoundly essential role as the glue that binds together decentralized services into holistic business applications. They not only help overcome technical hurdles introduced by distribution but also create order for organizational governance.

Microservices promise more agile delivery of new capabilities through independently developable units aligned to business domains. However, teams still face cross-cutting operational concerns like security, traffic management, and failure handling that divert focus from coding differentiating business logic.

API gateways promote velocity by providing these functionalities out of the box as reusable services. Developers avoid reinventing non-core modules and can dedicate more strategic attention to mission-critical code. Enterprises can consolidate scarce skills like security architects onto gateway administration rather than fragmented duplication across microservices teams.

Front-end applications no longer need to integrate directly with numerous backend microservices. Gateways minimize complexity for client developers by standardizing access through a single entry point and consistent interfaces. This simplifies building intuitive user experiences.

Teams can easily bind new microservices to customized gateway APIs optimized for particular app channels like mobile, web, devices, or partners. Backend migrations also cause no disruption as the gateway insulates callers from underlying implementation changes.

The promise of infinite horizontal scale relies on efficiently routing requests across ephemeral service instances. Microservices depend intrinsically on advanced load balancing, health checking, and resilient failover capabilities to deliver availability and handle spikes.

API gateways provide these scalability patterns consistently across all services so developers avoid having to rebuild the foundations before coding business logic. Teams can focus on rapid innovation rather than operational redundancy.

The decentralized ownership and control of microservices can quickly spiral into fragmented architectural entropy without careful governance. Gateways create a paradigm for coherent cross-cutting policies, standards, and controls by funneling all interaction through a single intermediary.

This consolidation point is perfectly positioned to enforce consistent security, compliance, performance monitoring, and documentation standards across all backend services regardless of internal technology or ownership. Gateways transform anarchy into order.

Here are best practices to effectively implement an API Gateway:

Plan for high availability: Architect the gateway for redundancy to avoid becoming a single point of failure.

Align with DevOps practices: Automate gateway configuration and manage it using infrastructure-as-code techniques.

Secure the gateway: Harden the gateway host and carefully manage access to administer the gateway software itself. 

Monitor performance: Collect metrics to monitor gateway latency impact and optimize configuration.

Leverage capabilities gradually: Start small and incrementally add gateway features to meet emerging needs.

Kong Gateway is a leading open-source API gateway and service mesh made for hybrid and multi-cloud environments. Kong provides essential features for secure, scalable microservices:

• Service discovery and routing
• Load balancing algorithms 
• Authentication & access control
• Rate limiting & throttling
• Logging & metrics
• Request tracing

Built on scalable architecture

Its high-performance architecture easily scales across nodes without bottlenecks. Kong uses a decentralized datastore for configuration. This aligns with scalability and resilience principles of microservices.

Extendibility 

Kong's plugin architecture lets you extend functionality for security, transformations, analytics and more.

Optimized for modern infrastructure

Kong easily integrates with orchestrators like Kubernetes and automation tools like Ansible and Terraform. This fits cloud-native development workflows. 

Adding an API gateway strategically positions organizations to unlock the full benefits of microservices architecture while mitigating common pitfalls. Kong Gateway is specifically designed to provide these microservices capabilities for modern application environments.