Chapter 16. Building Scalable Applications

Most production applications require more than one application instance. For example, a chat room system may have several lobby application instances running at the same time, as well as many chat room instances. In fact, instances of an application may be running on more than one server. Some of the good reasons to partition an application across multiple instances on one or more servers are as follows:

Performance

Each instance has a single ActionScript thread, which can constitute a bottleneck. Using multiple instances allows for multiple simultaneous threads.

Separation of resources

Clients that need common access to the same shared objects and streams can be grouped into separate instances.

Scalability

As the number of clients increases, a single server may not be able to handle the load. Adding CPUs, RAM, and network cards to a single server increases its capacity to handle more clients, but only up to a point. Placing separate instances on different servers allows applications to scale to accommodate as many clients as necessary.

Failover

When an instance or server fails, instances on another server can take over so that clients can reconnect and continue working.