Start with https://kubernetes.io/docs/tutorials/hello-minikube/ and proceed.
Read reference documentation on the same site whenever you need to dig somewhere.
It's awesome. You don't need any other websites. I was able to build a kubernetes cluster and right now deploying multi-service application and I have had enough technical information on this website alone.
As to answer your questions:
You can start with DB as an ordinary container in a statefulset deployment. It's similar to docker. You configure it with environment variables. Advanced approach is operators, but you don't need those for simple start.
Connection to DB is the same like docker. You use Kubernetes secrets instead of docker secrets and that's about it.
My message assumes that you're proficient with docker. If you're not, I suggest to first learning docker. May be you don't need Kubernetes for your scale at all. And if you do, most docker concepts make sense in Kubernetes anyway.
Most examples failed when then trying to use them together.
Also, jumping into directly K8 can be quite a jump.
I put this together to help SA Php group.
Starts off with just deploying directly on a server.
Then takes you to a full application deployed on K8 with auto SSL and DNS generation.
It needs a bit of a refresh :(
But finally coming out of being a bit over-committed, so should be updating in the next week or two.
Still some bits missing but it should cover all your basics
Id be more interesting on where kubernetes (redundancy) fits into traditional redundancy ?
Examples:
1. Do i still need gluster/ceph or do i use the longhorn thing ?
2. Db replication? Do i use the usual solutions of master-slaves and clusters or does multiple k-nodes take that over ?
3. Webserver LB with failover ? Do i use LB from hosting vendor, haproxy or does kubernetes have its own thing ??
From what I can tell as a kubernetes-noob the value is: 1) Reproducibility 2) Reliability via redundancy 3) AutoScaling.
All of the abkve has to some degree a previous/current solution , so which do i give up/replace with kubernetes-tool ?
Sorry yes Im a k-noob
Longhorn you can get up and working quickly.
Though if you are on a cloud provider just use their storage system.
2 K8 doesn't magically solve replication unfortunately.
Though there are helm charts that will automatically set up a replicated setup for you.
I still need to solve backups.
Once again if you are on a cloud provide. Just use their Db offering.
3 K8 doesn't have a default out of the box.
The repo shows you how to setup traefik to handle this.
On cloud providers they have normally integrated it with their lb already.
For me the large advantages are reproducibility and no vendor lock in.
Also give redundancy and quiet a bit of automation once set up.
Auto scaling is always tricky.
Lastly if you have the skills it can be far cheaper to run your own in metal.
If you don't the the time most likely would be better spent actually coding.
Depending where you are in the world and the relevant pay scales.