How to prevent docker from exiting after postgres start - postgresql

Question

I'm trying to build a customized postgres replication cluster in docker. I'm using postgres:9.6-alpine as my base image.
Here is my Dockerfiles which I'm using to build the slave container.
// Dockerfile
FROM postgres:9.6-alpine
ENV GOSU_VERSION 1.10
RUN set -ex; \
\
apk add --no-cache --virtual .gosu-deps \
dpkg \
gnupg \
openssl \
; \
\
dpkgArch="$(dpkg --print-architecture | awk -F- '{ print $NF }')"; \
wget -O /usr/local/bin/gosu "https://github.com/tianon/gosu/releases/download/$GOSU_VERSION/gosu-$dpkgArch"; \
wget -O /usr/local/bin/gosu.asc "https://github.com/tianon/gosu/releases/download/$GOSU_VERSION/gosu-$dpkgArch.asc"; \
\
# verify the signature
export GNUPGHOME="$(mktemp -d)"; \
gpg --keyserver ha.pool.sks-keyservers.net --recv-keys B42F6819007F00F88E364FD4036A9C25BF357DD4; \
gpg --batch --verify /usr/local/bin/gosu.asc /usr/local/bin/gosu; \
rm -r "$GNUPGHOME" /usr/local/bin/gosu.asc; \
\
chmod +x /usr/local/bin/gosu; \
# verify that the binary works
gosu nobody true; \
\
apk del .gosu-deps
RUN apk add --update iputils
RUN apk add --update htop
# COPY ./setup-slave.sh /docker-entrypoint-initdb.d
COPY ./docker-entrypoint.sh /docker-entrypoint.sh
RUN chmod +x /docker-entrypoint.sh
CMD ["gosu", "postgres", "pg_ctl", "-D/var/lib/postgresql/data", "start"]
And this is my docker-entrypoint.sh:
#!/bin/bash
if [ ! -s "$PGDATA/PG_VERSION" ]; then
echo '*:*:*:myuser:123456' > ~/.pgpass
chmod 0600 ~/.pgpass
until ping -c 1 -W 1 pg_master
do
echo "Waiting for master to ping..."
sleep 1s
done
until pg_basebackup -h pg_master -D ${PGDATA} -U arioo -vP -W
do
echo "Waiting for master to connect..."
sleep 1s
done
echo "host replication all 0.0.0.0/0 md5" >> "$PGDATA/pg_hba.conf"
set -e
cat >> ${PGDATA}/postgresql.conf <<EOF
wal_level = hot_standby
max_wal_senders = 8
wal_keep_segments = 32
hot_standby = off
EOF
cat > ${PGDATA}/recovery.conf <<EOF
standby_mode = on
primary_conninfo = 'host=pg_master port=5432 user=rep password=123456'
trigger_file = '/tmp/touch_me_to_promote_to_me_master'
EOF
chown postgres. ${PGDATA} -R
chmod 700 ${PGDATA} -R
fi
exec "$#"
The whole thing works just fine except for one thing. Docker immediately exits the slave container upon start. From my understanding pg_ctl start should start the postgres in foreground. But why is docker exiting still?
I use docker-compose to run the cluster.
I even tried putting an endless loop at end of the docker-entrypoint.sh like the code below and it's still exiting no matter what I do:
while true; do
sleep 1s
done

Answer 1

It seems that running postgres instead of pg_ctl start was the solution. pg_ctl is actually a utility to control the postgres daemon so it is logical that it runs postgres in the background.