Docker image build with shared library files

Question

Here is my file structure:

-- Dir1
---- Dockerfile
---- index.php
-- Dir2
---- Dockerfile
---- index.php
-- SharedLibrary
---- class.php

I want to build multiple images with docker-compose, and they both need the shared file in the other directory.

But Dockerfile can't add files with a relative path.

What does one usually do to resolve this?

By the way, it's not only run with local docker, so it should not handle with volume.

---

Additional Information:

• I want to make a shellscript to copy the required files to each directory and run docker-compose.
• I just want to know how to solve this issue gracefully.

Answer 1

You will have to move the Dockerfiles to the root directory (so above SharedLibrary in your case).

Docker has something called the "Build Context". Usually the directory the Dockerfile is in. The builder only has access to files in and below that, never above.

You can make two Dockerfiles like:

-<root>
-- Dir1
---- index.php
-- Dir2
---- index.php
-- SharedLibrary
---- class.php
-- Dockerfile.app1
-- Dockerfile.app1
-- docker-compose.yaml

And then specify those files in docker-compose.yaml.

---

Personally I would do it differently: I would merge the two into a multistage Dockerfile and specify a target in docker-compose.yaml. You'll end up with something like:

# docker-compose.yml
version: '3.8'
services:
  app1:
    build:
      context: .              # default
      dockerfile: Dockerfile  # default
      target: app1
  app2:
    build:
      context: .              # default
      dockerfile: Dockerfile  # default
      target: app2