Very easy:

I guess your situation is the following:

- You have a whole lot of datasources (db's, cubes, files, etc...)

- You use different datasources in different packages

- Some datasources might be used in several packages

First:

- Make sure you give the same datasources the same names in all packages

Then:

- In one of your packages, create a package configuration and choose type SQL server

- Create the variable you want and in your SQL Server database you'll see a table show-up called SSIS_configurations

- In that table you'll see a list of entries, one for every variable you created

- You can use these variables over several packages

- So link every datasource in every package to the right variable in your configuration table

- You can always add new variables to your table

When deploying to a different environment you can just copy the ssis_configurations table and change the values as you need

Our best practice is to create a seperate small SQL DB for this and just copy the entire db from development to production. That way, we have a set of values that apply in development and a seperate set in production.

Values I Always store in variables:

- OLE DB connection SERVERNAME

- OLE DB connection INITIAL CATALOG name

For the configurationDB connection we always use

- Fixed Servername: LOCALHOST

- Fixed DB-name: ETL_CONFIG

- Integrated Security login

Hope that helps you. If it's to vague, just let me know. I can go more in detail if necessary.