Keycloak server in docker fails to start in standalone mode?

I ran into the same issue. As it turned out, the key to the solution was the missing parameter "DB_USER=keycloak".

The Application tried to authenticate against the database using the username ''. This was indicated by the first error message.

WFLYCTL0113: '' is an invalid value for parameter user-name

Possibly the 4.x and 5.0.0 versions set the default user name to "keycloak" which was no longer the case in 6.0.0.

After adding the parameter DB_USER=keycloak to the list of environment variables, keycloak started up without any problems.

The problem no longer occurs now. I am voting to close the question.

I've also had an interesting observation to this issue, even in version 7.0.0. Alike the author mentions, postgres is selected if the host can resolve.

$ getent hosts postgres$ 92.242.140.21

What I've noticed is that if I issue a ping command at anything bizzare, even foobar, it evaluates to that same ip address. Example:

$ ping foobar$ PING foobar (92.242.140.21): 56 data bytes 

It seems that my ISP sends everything to a common endspace. I've solved the problem by using the -e DB_VENDOR=h2, to select the h2 db, and then had no issues. Alternatively, you can always spin up your own postgres version, or point to a legitimate endpoint. ( Not something fake provided by your ISP for DNS error handling )