first

.gitlab-ci.yml

+stages:
+  - build
+  - deploy
+
+variables:
+  GIT_DEPTH: "1"
+  CONTAINER_TEST_IMAGE: $CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG
+  CONTAINER_RELEASE_IMAGE: $CI_REGISTRY_IMAGE:latest
+
+before_script:
+  - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY
+
+build:
+  stage: build
+  tags: 
+    - docker
+  script:
+    - docker build --pull -t $CONTAINER_TEST_IMAGE .
+    - docker push $CONTAINER_TEST_IMAGE
+
+deploy_latest:
+  stage: deploy
+  tags: 
+    - docker
+  script:
+    - docker pull $CONTAINER_TEST_IMAGE
+    - docker tag $CONTAINER_TEST_IMAGE $CONTAINER_RELEASE_IMAGE
+    - docker push $CONTAINER_RELEASE_IMAGE
+  only:
+    - master
+
+deploy_tag:
+  stage: deploy
+  tags: 
+    - docker
+  variables:
+    CONTAINER_TAG_IMAGE: $CI_REGISTRY_IMAGE:$CI_COMMIT_TAG
+  script:
+    - docker pull $CONTAINER_TEST_IMAGE
+    - docker tag $CONTAINER_TEST_IMAGE $CONTAINER_TAG_IMAGE
+    - docker push $CONTAINER_TAG_IMAGE
+  only:
+    - tags

Dockerfile

+FROM debian:buster-slim
+
+RUN apt update && apt install -y apt-cacher-ng gettext-base && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
+
+COPY ./acng.conf.template /etc/apt-cacher-ng/acng.conf.template
+COPY ./entrypoint.sh /usr/bin/entrypoint.sh
+
+RUN ln -s /dev/stdout /var/log/apt-cacher-ng/apt-cacher.log && ln -s /dev/stderr /var/log/apt-cacher-ng.err        
+
+EXPOSE 80/tcp
+
+ENTRYPOINT [ "/usr/bin/entrypoint.sh" ]
+CMD [ "/usr/sbin/apt-cacher-ng", "-c", "/etc/apt-cacher-ng" ]

entrypoint.sh

+#!/bin/bash
+cat /etc/apt-cacher-ng/acng.conf.template | envsubst > /etc/apt-cacher-ng/acng.conf
+
+"$@"