Req : Need APE & DB requirement in HA or not
Let me keep this very simple (I am not sure what modules/products you have in your environment but yet overall, it's the same concept):
1. When you say SolarWinds High Availability - we are mainly talking about MPE or APE (Main Polling Engine or Additional Pollers)
2. Yes, you will need to build another new APE/MPE and then make it your standby server. Say suppose you have one additional poller ABC if you want to have high availability for the same you need to build a new APE XYZ and then apply HA on these 2 boxes to pair them accordingly. (You might need to purchase HA license, in certain SolarWinds products you don't have to worry about additional HA license as its part of your existing package).
3. Now when you talk about DB, I am not sure where is your DB hosted - but if it's a Ent SQL DB then you can use "SQL Server Always On Availability Groups (AAG) to create high-availability for your DB"
Below 2 links should provide you with the details that you are looking for - Hope this helps
SolarWinds Platform High Availability deployment walk-through
High Availability in SolarWinds Platform products
Its' up to you what portions of your environment you want to HA. If you only want HA on the Main Polling Engine you can. You don't have to have HA on all your APEs or your database if you don't want to, but you risk having a single point of failure for those elements if you don't. SolarWinds HA only covers their servers, you will need to explore SQL high availability separately.
The short answer is no, you just need to add the HA system (which is sort of an APE, but not exactly) and no changes to your SQL server.
If you are concerned about HA, then I recommend that you at least get the Main Polling Engine HA'ed and then separately the SQL setup with an availability group. If either of those pieces are down the entire system is down. Then (if you don't already) get a couple additional web servers and put them behind a load balancer (and do not include the main polling engines web server in the load balancer).
Other items of thought.
With Additional web servers behind a load balancer, they don't share authentication information, so if users switch which ones they connect to they have to re-login. Not a big deal if you use SAML and integrated authentication. Basically just make sure the connections are "sticky" (or whatever your load balancer calls it) so they stay on the same web server most of the time.
Do you need to HA your additional polling engines? depends on the type and length of outage you are protecting against. If it's just for reboots during patches and upgrades... then no probably not. otherwise sure. As an alternative to HA for APE, you can just install another APE, and then it is also load sharing and you can move nodes to it as a manual HA solution (or even automate it).
Type of HA. When are setting up HA, there are two types. One of them shares a common IP (I don't do this one). The other method uses DNS name that is updated to the current active engine, which I do use. With the DNS method there IS significant downtime during the switch (and I cannot speak to the IP based HA method). The primary system has to initiate the DNS change, then shutdown all the services, and only then does it start to bring up the services on the secondary system. The web portal and everything is down during the switch, which for me is often a few minutes.
Many moons ago, it was possible to use HA during an upgrade to the SolarWinds product to reduce downtime... but now you have to disable HA to start the upgrade... so BLAH!
Just keep in mind that this is not a "noone will notice" type of HA. I'm sure it will get better over time, and it's still good protection incase the polling engine dies unexpectedly during a microsoft patch.
