Putting applications or parts of the Grid in an offline state

In the ION Grid it is possible to prevent new client requests from being accepted by the server applications. This state is called offline. When some part of the grid is offline, it will no longer accept new requests but ongoing requests will be allowed to finish. This is ideal for situations when parts of a grid need to be taken down but you do not want to simply kill nodes since that would terminate existing processes performed there. In this situation, you may start by having the grid enter an offline state. When all ongoing requests are completed, you can stop the nodes or the relevant parts.

A typical example is that you want to stop an application in order to perform some maintenance. Just stopping all application nodes could perhaps result in some ongoing processing being terminated prematurely. The solution is to first put the application in an offline state. This prevents clients from calling the application with more requests. When all ongoing requests are finished, you may safely stop the application.

An important implication of an application being in an offline state is that nodes will no longer be automatically started even if the application has bindings that are configured to maintain a minimum number of running nodes. If an application has bindings of this type, it will be impossible to stop the application without also putting it in an offline state. This is because not doing so would cause the grid to automatically start new nodes to replace the stopped one.

The following entities may be put in an offline state:

• The entire Grid
• Individual hosts within the Grid
• Applications
• Individual application nodes

The following procedures describe how to put different parts of the grid in an offline state. Getting them on-line again is done in the same way.