You can run a normal postgres DB alongside EdgeDB. You can use a regular Postgres cluster and create your pg databases in it and at the same time point EdgeDB to the cluster

    docker run --name edgedb -e EDGEDB_PASSWORD=secret \
    -e EDGEDB_POSTGRES_DSN='...' \ 
    -d edgedb/edgedb

RedCrowbar answered this question here [1]

[1] https://news.ycombinator.com/item?id=27815177