Considerations for selecting a topology
Advanced topologies involve deploying your application on multiple machines or logical partitions. Multiple machine environments extend basic single machine WebSphere Application Server configurations and increase the processing power and availability of the application server. In addition, you can upgrade applications from one machine to all machines in the configuration. The topics below discuss the major factors to consider when you choose a toplogy.
If availability is a concern, your primary goal is to avoid single points of failure. High availability topologies require both process redundancy and hardware redundancy. In addition, they typically use workload management to distribute the client workload across two or more physically separated machines that host multiple application server processes. In a single machine environment, you can use vertical scaling to create additional application servers, which improves application availability on a single machine. Each of these sample topologies provides one or more of the elements required to improve availability:
- HTTP server transport sample topology
- Reverse proxy (IP forwarding) sample topology
- Demilitarized zone sample topology
- Vertical scaling sample topology
- Horizontal scaling sample topology
- Horizontal scaling with high-availability Apache Web server
- Horizontal scaling with Network Dispatcher sample topology
- Multiple WebSphere Application Server cells sample topology
- Sample combined topology
Note: Vertical scaling on a single machine provides process redundancy and can improve the overall efficiency of your applications. However, the machine becomes a single point of failure. As a result, vertical scaling alone does not ensure high availability.
If you are concerned about security, you can use firewalls to separate the Web server from the application server. Logical partitioning (LPAR) on iSeries provides the process isolation necessary to support the use of firewalls on a single iSeries server. See Firewalls and demilitarized zone (DMZ) configurations for more information. These sample topologies outline the basic DMZ configuration:
- Demilitarized zone (DMZ) sample topology
- HTTP server transport sample topology
- Reverse proxy (IP forwarding) sample topology
With WebSphere Application Server for iSeries, a single application server is adequate for most workloads. If you experience performance or throughput bottlenecks, you can add application servers to increase the processing speed and power of your application. These sample topologies improve performance and throughput:
- Vertical scaling sample topology
- Horizontal scaling sample topology
- Horizontal scaling with high-availability Apache Web server
- Horizontal scaling with Network Dispatcher sample topology
- Multiple WebSphere Application Server cells sample topology
- Sample combined topology
The topology of the system affects how easily you can update its hardware and software. If your topology includes multiple machines, you can take individual machines offline to perform hardware and software upgrades without interrupting your application. These sample topologies allow you to maintain your application server environment without compromising application availability:
- Horizontal scaling sample topology
- Horizontal scaling with high-availability Apache Web server
- Horizontal scaling with Network Dispatcher sample topology
- Multiple WebSphere Application Server cells sample topology
- Sample combined topology
For stateful applications and applications that run on multiple machines or application servers, it is important to maintain session state between client HTTP requests. Multiple multiple application server processes can share session state information if you save that information. See Sessions for more information.