Current archipel nodes number not enough for grandpa Block finalized consensus

[branciard]

If one validator node is down. There is 2 nodes remaining. There is block production but never finalized because 2 more signatures are required (2/3) expect the block producer. To support a node failure, the minimum required archipel nodes is 4.

Possible solutions for the setup a 3 HA validator polkadot : archipel A, archipel B, archipel C :

1. Add one archipel node in sentry mode in each archipel A,B,C.
   ( more nodes ..., not cool )

2. Replace 1 external sentry with a sentry mode in each archipel A,B,C.
   ( not cool)

3. Gather archipel A ( 3 nodes), B( 3 nodes), C( 3 nodes) in one chain. 2/3 finality = 9*2/3 = 6 nodes. Support 3 down nodes. orchestrator must filter A,B,C to operate. I will test this third solution.
   (cool : no more nodes and use external sentry as today

4. ?

With the previous old substrate we haven't' seen this problem because I think it was undercover by this bugs : paritytech/substrate#6341
Events on not finalized chain where also propagated. Now that this substrate bug is fixed. We see that when needs 3 nodes up to have a finalized chain and catch events ( addMetrics, SetLeader etc ...). 3 min nodes up means 4 archipel nodes min for our HA