Clustering

PopChart Server User Guide 4.0.5

HTTP Redirector Configuration

The PopChart HTTP redirectors are often an integral part of PopChart Cluster implementations. For the most part, configuration of the redirectors is covered in greater detail in Chapter 12, "HTTP Redirection." However, clustering may affect the value that you set the server address to in the initialization parameters or the configuration file.

When using the PopChart Cluster, PopChart Embedder will encode a primary and backup PopChart Server address into the image request that it embeds in a web page. When the redirector sees this request for an image, instead of forwarding it to the address in its configuration settings, it first tries to contact the primary PopChart Server. If that request fails, then it makes the request to the backup server. Only when both the primary and backup servers fail will it try to forward the request to the address specified in its configuration settings.

Still, it is important that you set the server address in the HTTP redirector settings properly. If a load balancer is between the redirector and the PopChart Cluster, then the address and port you should use for configuring the redirector is the virtual IP and port exposed by the load balancer (see the next section for important information about load balancing and HTTP redirection).

If there is not a load balancer, or if the redirector has direct access to the PopChart Servers in the PopChart Cluster without going through the load balancer, then you need to configure the redirector with the address of one of the PopChart Servers.

Using Load Balancing with HTTP Redirection

When you use a load balancer to create a virtual IP address for your PopChart cluster and an PopChart HTTP redirector is used between the client and the load balancer (i.e. the redirector forwards requests to the virtual IP address) you must check the Using a Software/Hardware Load Balancer box on the Settings > Clustering page of the Administration Console.

If you do not turn this on, then the redirector will try to talk to one of thePopChart Servers on the other side of the load balancer using its real IP address. Most load balancers will not direct communication, and thus the request will fail.