What is Initial command block?

What is an initial command? 

Commands which are executed only once on the first container after the first deploying a service. As an example, you can use it for populate database or migration.

Why nothing happens when I try to change it? 

You can run initial commands again using "Destroy and redeploy" button.

If you used Initial commands for database population you should clean up it at first. As one of the examples, you can also use Destroy and redeploy for that.

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