One-time backup via wal-e doesn't work due to no docket

[cadavre]

I ran a compose with postgres and timescaledb-wale – both sharing same volume mounted at /var/lib/postgres/data. Inside timescaledb-wale container I can see the volume with data. But when I try to exec simple wal-e backup-push /var/lib/postgresql/data I get an error:

psql: could not connect to server: No such file or directory
	Is the server running locally and accepting
	connections on Unix domain socket "/tmp/.s.PGSQL.5432"?
wal_e.main   ERROR    MSG: could not run one or more external programs WAL-E depends upon
        DETAIL: Could not get a connection to the database: note that superuser access
        is required
        Could not run the following programs, are they installed? psql
        STRUCTURED: time=2019-11-28T21:09:19.129528-00 pid=58

It looks like wal-e calling psql which obviously isn't running in wale container. I'm newbie to wal-e. Could you point me how to make a single backup via your image?