How to persist data using a postgres database, Docker, and Kubernetes? - postgresql

Question

I am trying to mount a persistent disk on my container which runs a Postgres custom image. I am using Kubernetes and following this tutorial.
This is my db_pod.yaml file:
apiVersion: v1
kind: Pod
metadata:
name: lp-db
labels:
name: lp-db
spec:
containers:
- image: my_username/my-db
name: my-db
ports:
- containerPort: 5432
name: my-db
volumeMounts:
- name: pg-data
mountPath: /var/lib/postgresql/data
volumes:
- name: pg-data
gcePersistentDisk:
pdName: my-db-disk
fsType: ext4
I create the disk using the command gcloud compute disks create --size 200GB my-db-disk.
However, when I run the pod, delete it, and then run it again (like in the tutorial) my data is not persisted.
I tried multiple versions of this file, including with PersistentVolumes and PersistentVolumeClaims, I tried changing the mountPath, but to no success.
Edit
Dockerfile for creating the Postgres image:
FROM ubuntu:trusty
RUN rm /bin/sh && \
ln -s /bin/bash /bin/sh
# Get Postgres
RUN echo "deb http://apt.postgresql.org/pub/repos/apt/ trusty-pgdg main" >> /etc/apt/sources.list.d/pgdg.list
RUN apt-get update && \
apt-get install -y wget
RUN wget --quiet -O - https://www.postgresql.org/media/keys/ACCC4CF8.asc | sudo apt-key add -
# Install virtualenv (will be needed later)
RUN apt-get update && \
apt-get install -y \
libjpeg-dev \
libpq-dev \
postgresql-9.4 \
python-dev \
python-pip \
python-virtualenv \
strace \
supervisor
# Grab gosu for easy step-down from root
RUN gpg --keyserver pool.sks-keyservers.net --recv-keys B42F6819007F00F88E364FD4036A9C25BF357DD4
RUN apt-get update && apt-get install -y --no-install-recommends ca-certificates wget && rm -rf /var/lib/apt/lists/* \
&& wget -O /usr/local/bin/gosu "https://github.com/tianon/gosu/releases/download/1.2/gosu-$(dpkg --print-architecture)" \
&& wget -O /usr/local/bin/gosu.asc "https://github.com/tianon/gosu/releases/download/1.2/gosu-$(dpkg --print-architecture).asc" \
&& gpg --verify /usr/local/bin/gosu.asc \
&& rm /usr/local/bin/gosu.asc \
&& chmod +x /usr/local/bin/gosu \
&& apt-get purge -y --auto-remove ca-certificates wget
# make the "en_US.UTF-8" locale so postgres will be utf-8 enabled by default
RUN apt-get update && apt-get install -y locales && rm -rf /var/lib/apt/lists/* \
&& localedef -i en_US -c -f UTF-8 -A /usr/share/locale/locale.alias en_US.UTF-8
ENV LANG en_US.utf8
# Adjust PostgreSQL configuration so that remote connections to the database are possible.
RUN echo "host all all 0.0.0.0/0 md5" >> /etc/postgresql/9.4/main/pg_hba.conf
# And add ``listen_addresses`` to ``/etc/postgresql/9.4/main/postgresql.conf``
RUN echo "listen_addresses='*'" >> /etc/postgresql/9.4/main/postgresql.conf
RUN echo "log_directory='/var/log/postgresql'" >> /etc/postgresql/9.4/main/postgresql.conf
# Add all code from the project and all config files
WORKDIR /home/projects/my-project
COPY . .
# Add VOLUMEs to allow backup of config, logs and databases
ENV PGDATA /var/lib/postgresql/data
VOLUME /var/lib/postgresql/data
# Expose an entrypoint and a port
RUN chmod +x scripts/sh/*
EXPOSE 5432
ENTRYPOINT ["scripts/sh/entrypoint-postgres.sh"]
And entrypoint script:
echo " I am " && gosu postgres whoami
gosu postgres /etc/init.d/postgresql start && echo 'Started postgres'
gosu postgres psql --command "CREATE USER myuser WITH SUPERUSER PASSWORD 'mypassword';" && echo 'Created user'
gosu postgres createdb -O myuser mydb && echo 'Created db'
# This just keeps the container alive.
tail -F /var/log/postgresql/postgresql-9.4-main.log

Answer 1

In the end, it seems that the real problem was the fact that I was trying to create the database from my entrypoint script.
Things such as creating a db or a user should be done at container creation time so I ended up using the standard Postgres image, which actually provides a simple and easy way to create an user and a db.
This is the fully functional configuration file for Postgres.
apiVersion: v1
kind: Pod
metadata:
name: postgres
labels:
name: postgres
spec:
containers:
- name: postgres
image: postgres
env:
- name: PGDATA
value: /var/lib/postgresql/data/pgdata
- name: POSTGRES_USER
value: myuser
- name: POSTGRES_PASSWORD
value: mypassword
- name: POSTGRES_DB
value: mydb
ports:
- containerPort: 5432
volumeMounts:
- mountPath: /var/lib/postgresql/data
name: pg-data
volumes:
- name: pg-data
persistentVolumeClaim:
claimName: pg-data-claim
Thanks to all those who helped me :)

Answer 2

does your custom postgresql persist data at /var/lib/postgresql/data?
are you able to get logs from your postgresql container and spot anything interesting?
when your pod is running, can you see the mountpoints inside your container and check the persistent disk is there?

Answer 3

I followed this scenario and I was able to persist my data by changing the mountPath to /var/lib/postgresql and also reproduced using cassandra (i.e. /var/lib/cassandra for mountPath)
I was able to delete/restart pods from different nodes/hosts and still see my "users" table and the data I previously entered. However, I was not using a custom image, I just used standard docker images.