Use the following to configure PostgreSQL and Keycloak. The key is to run this against a stopped Keycloak (using a fresh install). Save the below to something like setup-keycloak.cli:
embed-server --server-config=standalone.xml --std-out=echo
batch
#
# remove the default provided datasource
#
/subsystem=datasources/data-source=KeycloakDS/:remove
#
# add them
#
module add --name=org.postgres --resources=/path/to/postgresql-42.2.10.jar --dependencies=javax.api,javax.transaction.api
/subsystem=datasources/jdbc-driver=postgres:add(driver-name="postgres",driver-module-name="org.postgres",driver-class-name=org.postgresql.Driver)
/subsystem=datasources/data-source=KeycloakDS/:add(connection-url=jdbc:postgresql://localhost:5432/keycloak_database,driver-name=postgres,jndi-name=java:jboss/datasources/KeycloakDS,initial-pool-size=4,max-pool-size=64,min-pool-size=4,password=keycloak_user,user-name=keycloak_pass)
run-batch
Then run this with $KEYCLOAK_HOME/bin/jboss.sh --file=setup-keycloak.cli.
This removes the KeycloakDS datasource, adds the PostgreSQL module, and recreates the KeycloakDS datasource with your parameters. You can use this to reproduce the configuration any time as long as you have a local copy of the PostgreSQL JDBC driver.