使用docker-compose为AWS CodeBuild创建自定义构建映像

Question

I'm trying to create a custom docker image in order to use it as build image with AWS CodeBuild. It works fine if I just do docker build against Dockerfile with set up environment. But now I need to add a postgres instance to run the tests against. So I thought using docker-compose would do the trick. However I'm failing to figure out how to make it work. It seems like the static part of the composition (the image from Dockerfile) just stops right away when I try docker-compose up , since there is no entry point. At this point I can connect to db instance by running docker-compose run db psql -h db -U testdb -d testdb . But when I build and feed it to the script provided by AWS, it runs fine until my tests try to reach the DB-server. This is where it fail with timeout, as if there was no db instance.

Configs look like this:

version: '3.7'

services:
  api-build:
    tty: true
    build: ./api_build
    image: api-build
    depends_on:
      - db

  db:
    image: postgres:10-alpine
    restart: always
    environment:
      POSTGRES_USER: testdb
      POSTGRES_PASSWORD: testdb

And Dockerfile under ./api_build :

FROM alpine:3.8

FROM ruby:2.3-alpine as rb

RUN apk update && apk upgrade && \
      echo @edge http://nl.alpinelinux.org/alpine/edge/community >> /etc/apk/repositories && \
      echo @edge http://nl.alpinelinux.org/alpine/edge/main >> /etc/apk/repositories

RUN apk add --no-cache \
      alpine-sdk \
      tzdata \
      libxml2-dev \
      libxslt-dev \
      libpq \
      postgresql-dev \
      elixir \
      erlang

UPDATE: I just realized that docker-compose build just builds parts of composition if it's needed (eg Docker file updated), so does that mean there's no way to create an image using docker compose? Or am I doing something very wrong?

Answer 1

Since there are no answers I'll try to answer it myself. I'm not sure if it's gonna be useful, but I found out that I had some misconceptions concerning Docker, which prevented me from seeing a solution or the lack of.

1) What I didn't realize is that docker-compose is used for orchestration of container compositions, it cannot be built into a single image that contains all services that you need.

2) Multi-stage builds sounded exciting and a bit magical until I figured out that every next stage starts image from scratch. The only thing you can do is copy some files from previous stages (if aliased with AS ). It's still cool, but copying manually an installation with hundreds of files might (and will) become a nightmare.

3) Docker is designed to have only one process running inside of the container, but it doesn't mean it can't run multiple processes. So the solution for my problem was using a supervisor. S6 in particular, which is said to be lightweight, which is exactly what I needed with tiny Alpine images.

I ended up deploying s6-overlay from just-containers :

RUN curl -L -s https://github.com/just-containers/s6-overlay/releases/download/v1.21.4.0/s6-overlay-amd64.tar.gz \
      | tar xvzf - -C /

ENTRYPOINT [ "/init" ]

It provides /etc/services.d directory where service scripts go. For example for postgresql, the minimal example would be (in /etc/services.d/postgres/run):

#!/usr/bin/execlineb -P
s6-setuidgid postgres
postgres -D /usr/local/pgsql/data

Pretty much that's it.