Site provisioning from SharePoint (online) UI - CSOM, REST, Azure? What is the best approach?

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Deleted wrote:

I think a part is right Bill_Ayers1 jcgonzalezmartin but if you use functions be carefull when you have a large site to provision the function will have a time out.

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Indeed, and for functions the connection has to stay open during the duration. Spinning up old style site collection still usually takes 10+ minutes, so an always on webjob or similar might be a more stable approach.

For my sample, polling the site order list works fine, and we have it in production. But if you create many sites right away, the last person is in for a white as it does things synchronously. Which means, you need to look at the scenario at hand, and architect the complexity needed to solve your scenario. How many moving parts do you need to make it work for you?