[SOLVED] Install build-essential in Docker image without having to do `apt-get update`?

Issue

I have a Dockerfile which starts with the following:

FROM python:3.7-slim

RUN apt-get update && apt-get install build-essential -y

Problem is, this layer is always changing, so when I run docker build -t <mytag> ., this layer (and subsequent ones) run again, which takes up significant time.

Is there a way to install build-essential in my Dockerfile in a layer which doesn't constantly change?

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EDIT: I had a COPY line before RUN, which I removed from the question as I didn't want to include the names of private files, but it didn't occur to me that that was what was making the build re-run from this step.

Solution

Create a base image which contains:

FROM python:3.7-slim

RUN apt-get update && apt-get install build-essential -y

Build it:

docker build -t mybase .

Then use it for new images:

FROM mybase

Answered By - LinPy

Answer Checked By - Pedro (WPSolving Volunteer)