What is an Application Gateway?

An application gateway, also known as an application delivery controller (ADC) or web application firewall (WAF), is a purpose-built network appliance or software solution designed to optimize, accelerate, and secure application delivery for both traditional and modern applications. Sitting between clients and application servers, they help improve overall performance and availability, remove bottlenecks, prevent denial of service (DoS) attacks, and ensure only authorized users can access applications.

Hardware vs Software Gateways
They are available as both hardware and software solutions. Hardware Application Gateway are dedicated physical devices designed specifically for high throughput and optimized performance. They use network processors, memory, and SSD storage to distribute traffic efficiently. Software gateways run as a virtual application on commodity servers and hypervisors. While they don't match dedicated hardware performance, software gateways are more cost-effective, offer easier scalability, and can be deployed as virtual appliances in private and public clouds.

Load Balancing
One of the core functions of an application gateway is load balancing. It distributes incoming application traffic evenly across backend servers to optimize resource utilization and prevent any single server from becoming overwhelmed. Advanced load balancing algorithms consider server capacity, response times, availability, and other factors to route each connection to the best server. Sticky sessions ensure requests from the same user or session are directed to the same application instance for a consistent experience.

Compression and Caching
They help accelerate application delivery through compression and caching. Compression reduces bandwidth usage and speeds up transfers by encoding content before it's sent to clients. Caching stores frequently requested static and dynamic content in memory for ultra-fast retrieval, offloading backend servers. Gateway caches can be configured based on things like URI, cookie values, headers and cache expiration policies. Cached responses are often already pre-compressed.

SSL Offloading
Terminating secure SSL/TLS connections at the gateway instead of backend servers improves performance and security. It prevents the overhead of encryption/decryption from slowing down applications. Gateways can handle thousands of encrypted connections versus much lower limits on individual application servers. Offloading also simplifies certificate and key management since there is only one point of encryption on the network.

High Availability
Large companies require highly available applications that never go down. Application gateways support various high availability configurations and features to ensure continuous operation even during server failures or maintenance. Active-active and active-standby clusters, load sharing across datacenters, automatic failover mechanisms, and health monitoring are common ways gateways provide application high availability and disaster recovery.

Web Application Firewall
They often integrate web application firewall (WAF) capabilities to inspect HTTP traffic in layers 7 and above of the OSI model. They identify and block common exploits like SQL injection attacks, cross-site scripting (XSS), file inclusion vulnerabilities, and other web app vulnerabilities before reaching backend systems. WAF rules are updated continuously based on the latest attacks and threats to fortify application defenses automatically.

Static Asset Optimization
Application gateways optimize delivery of bulky static assets like images, videos, scripts and CSS files which account for most of today's web traffic and bandwidth usage. Using HTTP/2 servers push and caching, gateways pre-load assets and only push what's necessary to minimize page load times. Brotli, Gzip and other compression algorithms shrink filesizes. Image optimizations like cropping unnecessary pixels and converting to web friendly formats also improve performance.

API Security and Management
More applications leverage RESTful APIs for building modular services and connecting internal/external systems. Gateways provide API management functions like end-to-end security with TLS encryption, throttling to prevent floods or DDoS, authorization with OAuth, monitoring performance and usage. Advanced gateways translate protocols, aggregate related APIs under a single path, add documentation and tools to securely publish, consume and manage entire API programs.

Routing and Traffic Steering
Instead of dumb load balancing, advanced gateways support complex traffic management capabilities. Request headers, URL parameters and other metadata is extracted to make intelligent routing decisions. Dynamic traffic steering routes requests between environments like dev/test and production. Geo-routing ensures users are directed to servers with the lowest latency. Gateways also support blue/green deployments, canary testing and dark launching of new code without impacting existing services.

Advanced configurations allow mapping requests to multiple pools of applications. They also check backend health and availability, have options for retries, timeouts and error management. These routing features enable sophisticated implementation of traffic shift patterns as applications evolve.

API and Microservices Integration
Modern applications leverage microservices architectures split into independently deployable units managed through APIs/protocols like REST, GraphQL, gRPC etc. Application gateways can front public APIs, handle routing and load balancing between microservices, assist service discovery, perform access control and protocol translation between services using different technologies. With dynamic routing based on real-time conditions, they form the integration layer between APIs and consuming systems.

Monitoring and Analytics
Comprehensive visibility into applications is critical for performance tuning, capacity planning and issue resolution. Leading gateways integrate robust monitoring dashboards with analytic functions like real-user monitoring (RUM), synthetic transaction monitoring, error tracking and debugging capabilities. They provide detailed logs, stats on throughput, response times, cache hits etc. to gain insights into traffic patterns and catch potential bottlenecks before users notice. Gateway metrics feed into APM and monitoring platforms.

Application gateways have evolved far beyond basic load balancing and fulfil a strategic role in modern digital experience and infrastructure delivery. With their breadth of capabilities, they help optimize, secure and future proof business critical applications for growth while simplifying management overhead. Both software and hardware options are suitable depending on performance needs, licensing models and deployment preferences.