Q:

How to add worker role to exsisting cloud service on azure

I need to implement automated db backup for project, which located as cloud service on azure.
I followed this manual to do it, but I can't find, how to add worker role to exsisting project, if I've already had package and configuration file.
If I try to update curent instance of deployment on instances tab, I recive an error:
Removing role <SiteName>.Web will cause loss of data stored locally on instances of the role. Repeat this operation and specify 'Force'. The long running operation tracking ID was: <ID>.

A:

As you mentioned that you do have new package including new worker role, does your package include the previous worker role in it? If this a new worker role application or have you added a new worker role to your existing web role project and in this case you have both old webrole and newer worker role. 
I can explain you how update service works with Windows Azure as below:
With Windows Azure when your update your current running instance, the update package still needed full configuration and application code (including all roles new and old). When you update the service at portal you have option to either update all services or specific role and that is available in update window inside the drop down list. So if your current running service has web and worker role and you want to update only one specific role, you select the specific role form the drop down list and only that role will be updated while other role will be untouched. And if your select "All", all roles will be updated using the package content. So if you update one role, all roles, or all roles, your package must contain full configuration in it and depend on your selection, the role will be updated.  
In your case you want to add a new role to current running service so from the drop down you would select "All" option and so new role can be added to your current running service however  your existing service will experience downtime because major configuration is needed to run two separate role under one VIP. 
About your error, what I am suspecting is that your package does not contain the current running service configuration in it so when you try updating, the update process thinks that your just want delete the current running process and replace with new worker role. 

