optimise multiple execution of same command - Docker - postgresql

Question

I am trying to install and configure postgresql-client-11 on my ubuntu18:04. I understand that we need to perform a few extra steps shown below to do the same (Source: https://www.itzgeek.com/how-tos/linux/ubuntu-how-tos/how-to-install-postgresql-10-on-ubuntu-18-04-lts.html)
wget -q https://www.postgresql.org/media/keys/ACCC4CF8.asc -O- | sudo apt-key add -
echo "deb http://apt.postgresql.org/pub/repos/apt/ bionic-pgdg main" | sudo tee /etc/apt/sources.list.d/postgresql.list
sudo apt-get update
sudo apt-get install -y postgresql-client-11
I am achieving it with the following
RUN apt-get update && apt-get dist-upgrade -y && apt-get install -y wget && apt-get install -y gnupg2
RUN echo "deb http://apt.postgresql.org/pub/repos/apt/ bionic-pgdg main" | tee /etc/apt/sources.list.d/postgresql.list
RUN wget https://www.postgresql.org/media/keys/ACCC4CF8.asc
RUN apt-key add ACCC4CF8.asc
RUN apt-get update && apt-get dist-upgrade -y && DEBIAN_FRONTEND=noninteractive apt-get install -y nodejs && rm -rf /var/lib/apt/lists/*
I am executing the same command RUN apt-get update && apt-get dist-upgrade -y twice.
Is there any way to optimise the above and not have redundant commands.

Answer 1

You can tweak this a little, but fundamentally you need two RUN apt-get update && apt-get install lines. The essential dependency chain is:
The last apt-get install line depends on having the upstream PostgreSQL repository available
You can't apt-get install from a repository until you apt-get update from it
You can't do that apt-get update without the preceding lines to add the sources.list line and load the public key
You can't get the public key without wget and gnupg
Which requires an additional apt-get install and preceding apt-get update
There's no particular need to run dist-upgrade twice and I'd skip it the first time (and maybe the second time: the Docker Hub ubuntu image is updated pretty regularly). You can combine multiple apt-get install commands together, and if you have the rm clause in there you need to run it every time. You also might consider whether you need a client library newer than what Ubuntu packages; if an older client library will work fine you can simplify this significantly.
So I might wind up somewhere like:
# Install prerequisites to install prerequisites
RUN apt-get update \
&& DEBIAN_FRONTEND=noninteractive apt-get install --no-install-recommends --assume-yes \
gnupg2 \
wget \
&& rm -rf /var/lib/apt/lists/*
# Configure upstream PostgreSQL repository
RUN echo "deb http://apt.postgresql.org/pub/repos/apt/ bionic-pgdg main" | tee /etc/apt/sources.list.d/postgresql.list \
&& wget https://www.postgresql.org/media/keys/ACCC4CF8.asc \
&& apt-key add ACCC4CF8.asc
# Actually install the packages we need
RUN apt-get update && \
&& DEBIAN_FRONTEND=noninteractive apt-get dist-upgrade -y \
&& DEBIAN_FRONTEND=noninteractive apt-get install --no-install-recommends --assume-yes \
nodejs \
postgresql-client-11 \
&& rm -rf /var/lib/apt/lists/*