Alfresco WebApp upgrade under High Availability environement

[zomurn]

Hello,

I'am wondering if, under HA environnement, ie with clustered EHCache and clustered DB engine, we are able to upgrade alfresco with transparency.
For example, suppose I have 2 nodes running, viewing each other through clustering (not necessarily through Load balancing).
Then I must stop the running node and deploy the upgrade version and the same for the second node.
It is not possible to have 2 nodes with a different webapp.
So in what it consist the concept of "High Availibily" ?
Alfresco Upgrades still require to shutdown all nodes and restart them one by one.

[zomurn]

Any help ?

[mrogers]

I think its safest to say that the HA stuff does not apply to upgrade scenarios.    However there may be a few special cases where upgrades can be done under load, it rather depends upon the change.

What the HA stuff will give you is the ability to adjust your processing nodes as required.   It would also give a degree of protection against hardware failure of one or more nodes.

[zomurn]

Finally, I'am going to setup two nodes : the second one will be a "warm stanby server" : all is replicated (mirror) ie : contentStore, Indexes and database.
This will be suited for : hot backup done without disturbing production server and hardware failure.
I would like one more feature : application always available, how to deploy new versions ?
In general big web application (like google ) how do they do to assure a 100% continuation ?

[mrogers]

It depends upon the application but upgrading under load is difficult for web applications.   There's a couple of strategies, one is to run the old and new versions in parallel and then switch over users as they establish new sessions.    That of course can cause data issues if the back ends are not the same.   If you are lucky you can run both web apps on the same database but if there's an incompatible business rule or schema change then that can be problematic.   A second approach is to use an adapter layer that takes the webapp's data and translates it for each version.

I think you will find that the most common approach for upgrade is a small planned downtime.

[zomurn]

OK thanks you for your answer, you gain one point more .