BUG #17191: Docker / buildx issue - An image created with buildx requires to set custom PGDATA location

The following bug has been logged on the website:

Bug reference: 17191
Logged by: Wlad
Email address: wlad@0trust.de
PostgreSQL version: 13.4
Operating system: linux
Description:

I noticed a different behavior of postgres docker containers depending on
whether the image was build with `docker build`
(normal Docker) or with `docker buildx build` (Moby BuildKit).

## Case 1 - the failing case (docker buildx / Moby BuildKit)

```dockerfile
# syntax=docker/dockerfile:1
FROM --platform=$BUILDPLATFORM postgres:13.4-alpine
ARG TARGETPLATFORM
ARG BUILDPLATFORM
RUN echo "Running on $BUILDPLATFORM, building EHRbase PostgreSQL DB for
$TARGETPLATFORM" > /log

# SHOW POSTGRES SERVER AND CLIENT VERSION
RUN postgres -V; \
psql -V

# SET DEFAULT VALUES FOR DATABASE USER AND PASSWORDS
ARG EHRBASE_USER="ehrbase"
ARG EHRBASE_PASSWORD="ehrbase"
ENV EHRBASE_USER=${EHRBASE_USER}
ENV EHRBASE_PASSWORD=${EHRBASE_PASSWORD}

# COPY DB SETUP SCRIPT TO POSTGRES's DEFAULT DOCKER ENTRYPOINT FOLDER
# NOTE: check postgres's docker docs for details
# https://hub.docker.com/_/postgres/
COPY scripts/db-setup.sql /docker-entrypoint-initdb.d/

# ALLOW CONNECTIONS FROM ALL ADRESSES & LISTEN TO ALL INTERFACES
# NOTE: locally works w/o this additional settings
RUN echo "host all all 0.0.0.0/0 scram-sha-256" >>
${PGDATA}/pg_hba.conf; \
echo "listen_addresses='*'" >> ${PGDATA}/postgresql.conf; \
ls -la ${PGDATA}

```

Build image with `docker buildx build --push
--platform=linux/arm64,linux/amd64 .`

The image created this way REQUIREs TO PROVIDE a custom PGDATA location,
otherwise it will exit i.e.

### with custom PGDATA location (succeeds)
```
docker run --name ehrdb \
-e POSTGRES_PASSWORD=mypostgres \
-e EHRBASE_USER=myuser \
-e EHRBASE_PASSWORD=mypassword \
-e PGDATA=/tmp \
-d -p 5432:5432 \
ehrbase/ehrbase-postgres:13.4
```

### without custom PGDATA location (fails)
```
docker run --name ehrdb \
-e POSTGRES_PASSWORD=mypostgres \
-e EHRBASE_USER=myuser \
-e EHRBASE_PASSWORD=mypassword \
-d -p 5432:5432 \
ehrbase/ehrbase-postgres:13.4

docker logs ehrdb

The files belonging to this database system will be owned by user

"postgres".
This user must also own the server process.

The database cluster will be initialized with locale "en_US.utf8".
The default database encoding has accordingly been set to "UTF8".
The default text search configuration will be set to "english".

Data page checksums are disabled.

initdb: error: directory "/var/lib/postgresql/data" exists but is not
empty
If you want to create a new database system, either remove or empty
the directory "/var/lib/postgresql/data" or run initdb
with an argument other than "/var/lib/postgresql/data".
```

## Case 2 (normal docker build)

Apart from

```
# syntax=docker/dockerfile:1
FROM --platform=$BUILDPLATFORM postgres:13.4-alpine
```
the Dockerfile below is identical with the one from Case 1.

```dockerfile
FROM postgres:13.4-alpine
ARG TARGETPLATFORM
ARG BUILDPLATFORM
RUN echo "Running on $BUILDPLATFORM, building EHRbase PostgreSQL DB for
$TARGETPLATFORM" > /log

# SHOW POSTGRES SERVER AND CLIENT VERSION
RUN postgres -V; \
psql -V

# SET DEFAULT VALUES FOR DATABASE USER AND PASSWORDS
ARG EHRBASE_USER="ehrbase"
ARG EHRBASE_PASSWORD="ehrbase"
ENV EHRBASE_USER=${EHRBASE_USER}
ENV EHRBASE_PASSWORD=${EHRBASE_PASSWORD}

# COPY DB SETUP SCRIPT TO POSTGRES's DEFAULT DOCKER ENTRYPOINT FOLDER
# NOTE: check postgres's docker docs for details
# https://hub.docker.com/_/postgres/
COPY scripts/db-setup.sql /docker-entrypoint-initdb.d/

# ALLOW CONNECTIONS FROM ALL ADRESSES & LISTEN TO ALL INTERFACES
# NOTE: locally works w/o this additional settings
RUN echo "host all all 0.0.0.0/0 scram-sha-256" >>
${PGDATA}/pg_hba.conf; \
echo "listen_addresses='*'" >> ${PGDATA}/postgresql.conf; \
ls -la ${PGDATA}
```

Build image with `docker build -t ehrbase/ehrbase-postgres:13.4 .`

#### The image created this way can be run with OR without providing a
custom PGDATA location, i.e.

### with custom PGDATA location
```
docker run --name ehrdb \
-e POSTGRES_PASSWORD=mypostgres \
-e EHRBASE_USER=myuser \
-e EHRBASE_PASSWORD=mypassword \
-e PGDATA=/tmp \
-d -p 5432:5432 \
ehrbase/ehrbase-postgres:13.4
```

### without custom PGDATA location
```
docker run --name ehrdb \
-e POSTGRES_PASSWORD=mypostgres \
-e EHRBASE_USER=myuser \
-e EHRBASE_PASSWORD=mypassword \
-d -p 5432:5432 \
ehrbase/ehrbase-postgres:13.4
```

For better readability find all above info MarkDown formated on Github Gist
https://gist.github.com/wlad/db6e99e46c5da8751d50d454479db42c