How can I install Rails plugin during the provision?

[tanin]

I saw that Exceptional and New Relic can do that.

They install a plugin during the plugin installation.

Could you give me some advice?

[Pedro Belo]

Hi there,

We're moving away from auto installing plugins or gems to user
applications. We won't support that in the official add-ons API, so as
old/custom add-ons (like Exceptional and New Relic) move to the newest
API we'll stop installing their plugins too.

Providers should still maintain gems or plugins when possible, but
users will be responsible for installing and upgrading those.

Thanks,
Pedro