A PostgreSQL database is required, you can spin up a PostgreSQL database with the bitnami PostgreSQL helm chart. Add the bitname repository:
helm repo add bitnami https://charts.bitnami.com/bitnami
And setup the Postgres database:
helm install druid bitnami/postgresql \
--version=11 \
--set auth.username=druid \
--set auth.password=druid \
--set auth.database=druid