thanks for posting this on q&a, its a great question ))
u can totally deploy both avs environments under the same subscription. microsoft allows that, no problem. but... there are some things to think about before u decide.
for the expressroute gateway part - yes, u can connect multiple avs instances to the same gateway. its actually a common setup when u want to keep things simple https://docs.microsoft.com/en-us/azure/azure-vmware/concepts-networking#expressroute
now, about subscriptions... if u use one subscription for both, its easier to manage billing and permissions. everything's in one place, less hassle. but! if something goes wrong with that subscription, both avs environments get affected. not ideal, right?
if u go with separate subscriptions, u get more isolation. one goes down, the other stays up. also, u can set different rbac rules for each. but then u gotta handle two bills, two sets of permissions... bit more work.
as well check this link https://docs.microsoft.com/en-us/azure/cost-management-billing/manage/create-subscription its about creating extra subscriptions if u need them.
worth looking into how much resources each avs will use. if they're both heavy, maybe separate subs help with quota limits. but if they're small, one sub could be simpler.
aha, and dont forget - u might wanna test this in a dev setup first. just to see how it feels ))
this might help in other tools too - when u plan multi environment setups, always think 'what if this breaks'. keeps u out of trouble later %))
let me know if u need more details, happy to help!
Alex
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