Hi
If i have 2 instance of keycloak (Instance A & Instance B) installed and both are using the same MySQL DB, will this means that if user authenticated on instance A he will be authenticated on instance B as well?
If not, then why? and How can i achieve that?
You need the two instances to form a cluster. If running in the same machine or same subnet, they will probably do that by default.
But if running in different subnets or in a container environment, you need to configure the cluster discovery mechanism.
Take a look at clustering section of the documentation: Server Installation and Configuration Guide