add ci and add ca-certificates

.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 ubuntu:latest AS downloader
+FROM debian:buster-slim AS downloader
 
 RUN apt update && \
     apt install -y curl wget
@@ -7,7 +7,11 @@ ADD downloader.sh downloader.sh
 
 RUN sh downloader.sh
 
-FROM ubuntu:latest
+FROM debian:buster-slim
+
+RUN apt update && \
+    apt install -y ca-certificates && \
+    rm -rf /var/lib/apt/lists/*
 
 COPY --from=downloader /smartdns.deb /
 
@@ -20,4 +24,4 @@ VOLUME [ "/etc/smartdns" ]
 
 ENTRYPOINT [ "smartdns" ]
 
-CMD ["-f -c /etc/smartdns/smartdns.conf"]
\ No newline at end of file
+CMD ["-f -c /etc/smartdns/smartdns.conf"]