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Application Deployment > Hot Deployment: Updating Applications without Bringing the System Down |
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Hot Deployment: Updating Applications without Bringing the System Down |
Avaya recommends that developers always attempt to design and create highly available Web applications, or Web applications that can be deployed or updated without bring the system down. This is referred to as "hot deployments". Typically, this is achieved using hardware or software solutions to achieve application updates utilizing multiple servers and a load balancer.
Hot deployments essentially use HTTP routing (load balancer or IP sprayer) to route requests away from the server that will be upgraded. With sticky sessions (or session affinity), all active sessions on the server are allowed to finish (or "drain") while other servers assume the load of the server that is being taken down. When all sessions have been drained, the application on the server can be stopped and the update applied
In such a case, the server does not actually have to stop unless common libraries are updated. This means that other applications on the server can continue to run uninterrupted.
After updating the application, it can be restarted and then traffic can be gradually routed to it to make sure that it is running properly. This approach also allows updates to be backed out if there are problems with the new application by routing requests back to the servers hosting the older application version.
Hot deployment approaches for developing Web application updates while maintaining application availability is widely documented on the Web for deployment to enterprise-level application servers.
Following are a handful of references, but the Web has many more:
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