Important Concepts and Options
When managing Web or Web Service applications, it is important to understand
the concepts of sessions and persistence
and how to take advantage of the various scalability options at you disposal.
Process Pooling allows you to
use your existing server resources much more efficiently. Load
Balancing allows you to extend your resources over multiple servers.
Security, Performance, Load
Balancing and Failover for our Web Applications
“SPLF” stands for Security, Performance, Load Balancing and Failover.
This special server is used as a manager and application collaborator
that provides services and resources to one or more DataFlex WebApp Servers
executing web applications.
The SPLF Server is the HTTP interface for DataFlex web and mobile applications.
It intercepts users’ HTTP requests and directs them to one or more connected
application servers. The application server(s) return application pages
and data through the SPLF server. The four valuable functions provided
by an SPLF server are:
- Security – The network
connection between the SPLF server and the application servers attached
to it can be configured using non-internet, Network Address Translation
(NAT) addresses and other firewall mechanisms. In such a configuration,
the SPLF server is internet connected – it has a public IP address.
The application server(s) connected to the SPLF server will have internal,
non-internet-exposed, NAT addresses that preclude direct access by
internet users. With this configuration, applications and, just as
importantly, application data, are never accessible from the internet
thereby providing a highly secure environment.
- Performance – When IIS
and DataFlex Web Framework applications are run on the same server
instance, a significant portion of the computing capacity of the server
is used by IIS – the Microsoft HTTP server program. This can materially
limit the computing capacity of the server available for applications
(sometimes as little as 50% of the server’s resources are available
for application processing). By moving the overhead of IIS to a separate
SPLF server, the majority of an application server’s resources can
be devoted to processing user requests. More server capacity = more
performance and more application processing power per application
server instance.
- Load Balancing – An SPLF
server can distribute or “balance” user requests among 2 to 255 clustered
DataFlex WebApp Servers for high-capacity application processing.
Each DataFlex WebApp Server will have the security and performance
benefits described above so the effect of multiple application servers
is cumulative.
- As load grows, overall application processing capacity can
scale easily and transparently by simply adding another application
server instance to the cluster and including it in the SPLF Server’s
list of available servers.
- If application server maintenance or upgrades are required,
temporarily removing an application server from the cluster stops
incoming requests to it and distributes the requests to other
available servers so offline operations can been performed.
- This flexible cluster design allows for the use of application
servers of varying capacities, for example older and newer systems,
and the assigning each server in the cluster with a load that
it is capable of processing.
- Failover - In addition
to distributing load, in the event that an application server in the
cluster fails, the SPLF server will automatically sense the failure,
remove the failed server from the cluster and distribute incoming
requests to or among the remaining active server(s).
A DataFlex SPLF server runs on its own dedicated server instance. To
keep licensing simple, the entitlement to connect to an SPLF server is
licensed as a low-cost add-on fee to the application server license price.
SPLF Servers can be connected to DataFlex WebApp Servers using either
Web Client or Web Application licensing.