What is an Application Gateway?
An application gateway acts as a reverse proxy server that sits in front of web servers and applications. It intercepts all incoming traffic to applications, terminating the incoming connections, and establishing new connections to applications servers. This allows it to offload processing of certain requests and responses to improve performance and add several security functions.
Application Traffic Management
One of the core functions of it is Application Gateway traffic management. It handles load balancing of incoming requests across multiple backend servers. This ensures no single server is overutilized and provides high availability. It can also implement features like caching static content, compression, SSL offloading etc to optimize application performance.
Requests are distributed across servers based on server health, load, and other metrics. Unhealthy servers are automatically taken out of load balancing rotation. Advanced routing rules can also be configured to match URI patterns and direct traffic to specific applications or versions.
Access Control and Authentication
Application gateways implement access control and user authentication to applications. Granular role and policy-based access controls can be configured based on user, group, IP address or other attributes. This restricts access to only authorized users for each application.
Authentication is also handled at the gateway before traffic reaches applications. Popular authentication protocols like Basic, Digest, NTLM, OAuth, OpenID Connect etc can be supported. Single Sign-On (SSO) allows users to access multiple applications with one set of credentials. Detailed authentication logs help with audit and compliance reporting.
Security Hardening
As the first point of contact for all inbound traffic, application gateways play a critical role in security hardening. They filter, inspect and validate all incoming requests to detect and block common exploits, vulnerabilities, malware and other threats.
Built-in web application firewall (WAF) rules and signatures identify common vulnerabilities like SQL injection, cross-site scripting (XSS) etc. Threat models, allow-lists and isolation policies only permit known good traffic further protecting backend applications. Malformed requests are rejected prior to application processing for additional protection.
Data and Traffic Encryption
Application gateways support TLS/SSL offloading where encryption and decryption of traffic happens at the gateway rather than application servers. This avoids costly cryptographic processing on applications. The gateway acts as a TLS endpoint terminating secure connections while backends communicate in plaintext.
Sensitive data traversing between clients and applications or even between gateway and backends can be further encrypted using options like IPsec, DTLS etc. Even if traffic is intercepted, it remains encrypted providing data-in-transit security. Encryption keys are managed centrally at the gateway.
Logging and Analytics
As a central access point, they have full visibility into all application traffic. Detailed logs capturing every request, response, session and security event provide a single source of truth. Logs are analyzed to gather insights, detect anomalies, troubleshoot issues and for regulatory compliance.
Customizable log formats and filters allow extracting specific fields. Logs are then forwarded to central log collection and analytics platforms for long-term storage and reporting. Pre-built as well as custom detections can also analyze logs to identify and alert on suspicious application behaviors in real-time.
Deployment Flexibility
Application gateways are designed for flexibility whether deployed on-premises, in public or private clouds or as a hybrid architecture. Their lightweight footprints make them suitable for virtual or container-based environments as well. Multiple deployment options exists ranging from dedicated appliances to virtual instances and containers.
High availability can be achieved through active-active or active-standby clustering. Redundancy ensures continuity of operations in the event of planned or unplanned outages. Centralized management provides a unified view and control across distributed deployment topologies for day-1 and day-2 operations.
In summary, they act as a critical part of the defense-in-depth strategy securing modern applications. Their abilities in traffic management, security hardening, encryption and analytics provide comprehensive visibility and protection needed for robust application security posture. With their flexibility of deployment and extensive feature-sets, application gateways continue scaling up to deliver application security at scale within enterprise environments.
