How well are data centers within the same region isolated for high availability?

As our SaaS solution grows I want to invest more in high availability.

My first thought was to use vpc peering to tie 3 data centers together, put a database server in each data center and then use them as a logical cluster (MaxScale or Galera). But, I noticed that DigitalOcean does not recommend running their own Managed Database solution across data centers for performance reasons.

As I considered the performance implications I also started to wonder if I was making the HA gain I had hoped for. I remember a few years ago a networking issue (configuration error I think) actually affected both NYC3 and NYC2.

So here is the real question. I haven’t had an outage in NYC3 in over 9 years. If there is an issue big enough to bring down NYC3, would it likely impact NYC1 and NYC2 as well? If that is the case, I might as well deploy my HA cluster in one datacenter, avoid the performance issue, and have disaster recover automation that could relaunch the solution in another data center in any available region.

I still like my idea of a cluster across NYC1, NYC2 and NYC3 but maybe that just isn’t realistic as a HA solution.