changing name to db-container now it works

db-container/Dockerfile

@@ -0,0 +1,17 @@
+FROM postgres:latest
+USER root
+ENV TZ=Australia/Melbourne
+RUN truncate -s0 /tmp/preseed.cfg && \
+       (echo "tzdata tzdata/Areas select Australia" >> /tmp/preseed.cfg) && \
+       (echo "tzdata tzdata/Zones/Australia select Melbourne" >> /tmp/preseed.cfg) && \
+       debconf-set-selections /tmp/preseed.cfg && \
+       rm -f /etc/timezone /etc/localtime && \
+       apt-get update && \
+       DEBIAN_FRONTEND=noninteractive DEBCONF_NONINTERACTIVE_SEEN=true \
+       apt-get install -y tzdata 
+## cleanup of files from setup
+RUN rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
+RUN apt-get update && apt-get -y install cron
+COPY crontab /etc/crontab
+EXPOSE 5432
+CMD ["sh", "-c", "cron ; /usr/local/bin/docker-entrypoint.sh postgres"]

db-container/crontab

@@ -0,0 +1 @@
+* * * * * root pg_dump -a --user=pa --table=person --table=refimg --table=person_refimg_link > /tmp/new_users.sql