Azure Application Gateway features
The following list outlines the main features of the Azure Application Gateway. These features help explain how this service can be a key component of any web application design:
■ Web application firewall (WAF) The Azure Application Gateway can act as a WAF, monitoring incoming traffic from clients and intercepting any malicious activities to provide centralized protection from well-known vulnerabilities for multiple web applications in your environment. You can host an application behind the WAF even if you have not yet been able to patch the vulnerabilities on the web servers themselves. You can centrally protect an application or even a large server farm that needs patching from a known vulnerability by patching the WAF. This serves as an interim solution until the application or server farm itself can be updated.
■ Multiple-site hosting Azure Application Gateway supports the use of multiple host, domain, or subdomain names on the same application gateway. So, you can use a single application gateway to handle web traffic for multiple web applications. This enables you to maximize your investment in the service by using each instance to its fullest capacity. You can map more than 100 web applications to a single application gateway. And, by using multi-site listeners, you can route traffic sent to a single public IP to different back-end server pools based on the URL request or host header.
■ Web-traffic redirection By redirecting web traffic meant for one port to another, you can mask the application ports used internally on the web application servers, which can improve the security of your web applications. Traffic redirection also enables you to centrally route HTTP traffic to HTTPS, ensuring that no unencrypted communication occurs between your clients and web services. Web-traffic redirection supports the following scenarios:
■ Global traffic redirection This type of redirection enables you to redirect all traffic from HTTP to HTTPS on a site or to any other non-standard port required by the web application.
■ Path-based redirection With this type of redirection, you can redirect HTTP to HTTPS or any other non-standard port only on specific site areas, such as traffic to /videos/* or /checkout/*.
■ Redirection to an external site This type of redirection allows you to redirect traffic to an external site.
Secure Sockets Layer/Transport Layer Security (SSL/TLS) termination You can use Azure Application Gateway to offload SSL/TLS processing for your web applications. This helps reduce the overhead of SSL/TLS encryption/decryption as well as server resource consumption. Traffic between the application gateway to the web application hosted internally behind it can be unencrypted. In some scenarios, however, you might need the back-end traffic to be encrypted for compliance or application-design reasons. Azure Application Gateway supports these types of end-to-end encryption scenarios, too.
Session affinity handling You can set up Azure Application Gateway to support cookie-based session affinity, thereby ensuring that any sessions that are interrupted or dropped will reconnect to the same server as before. This can be a critical requirement for some applications where a user’s session state is stored locally on the server.
Static virtual IP (VIP) assignment The Standard_v2 version of Azure Application Gateway supports the use of static VIP addresses, ensuring the VIP is maintained as-is for the lifetime of the application gateway.
Zone redundancy You can set up Azure Application Gateway to span multiple availability zones, thereby improving the gateway’s SLA and resiliency.
■ Path-based routing This enables you to analyze and route traffic based on the path indicated in the incoming web request. You can set up the application gateway to route traffic to different back-end servers or server pools based on the paths found in the request. So, content for different paths of a URL can be hosted on different servers or server pools, and the content itself can be optimized to deliver the best end-user experience possible.
■ Automatic scaling You can set up Azure Application Gateway to automatically scale up or down based on traffic load at any given time. You need not select the “perfect” size for the application gateway when you provision it, because the gateway can scale as needed as traffic grows over time.
■ Support for WebSocket and HTTP/2 traffic Azure Application Gateway natively supports WebSocket and HTTP/2 protocols. WebSocket is enabled by default and cannot be turned off. It allows full duplex communication between the web application server and client over long-running TCP connections, which can be optimized and used for multiple requests and responses. HTTP/2 protocols can be used only for client-to-application gateway communications. HTTP/2 is designed to function more efficiently than HTTP-based communications by eliminating the need for the constant polling required by HTTP to keep long-running sessions alive, which reduces the application gateway’s overhead with client communications. Both protocols are designed to work over ports 80 and 443, so you can easily incorporate them into an environment without making firewall changes.