How to pass file environment variable to container as file

GitLab CI/CD
1

Hi all,
I have Gitlab CE onpremise.
A dotnet core project has an (real)appsettings.json file store database connectionstrings.
I want to replace it with an (fake)appsettings.json like this:

{
  "ConnectionStrings": {
    "SQLConnection": "Server=$MSSQLSERVER; Database=$MSSQLDBNAME; User ID=$MSSSQLUSER; Password=$MSSQLPASS"
  }
}

Then pass environment variables from Gitlab cd/cd variables to container later.
I’m new to Gitlab ci/cd and I’m not a programmer so I think of 2 solutions :

Solution 1: Replace (fake)appsettings.json with (real)appsettings.json when building image

  • Create a (type) file key=appsettings_json variable in gitlab ci/cd variables , with value is content of (real)appsettings.json
  • Pass (type) file key=appsettings_json to Dockerfile when building image
.gitlab-ci.yml
build_image:
  stage: build
  image: docker:20.10.9
  services:
    - docker:20.10.9-dind
  variables:
    DOCKER_TLS_CERTDIR: "/certs"
  before_script:
    - docker login -u $REGISTRY_USER -p $REGISTRY_PASS
  script:
    - docker build --build-arg appsettings_json=$appsettings_json -f Dockerfile -t name:tag .
  • Create (real)appsettings.json file inside image
Dockerfile
FROM mcr.microsoft.com/dotnet/core/sdk:2.2 AS build
WORKDIR /app
COPY ./ ./
RUN echo $appsettings_json
RUN echo $appsettings_json > ./appsettings.json
RUN cat ./appsettings.json

But it doesn’t work , the $appsettings_json and appsettings.json are empty

Solution 2 :
Pass $MSSQLSERVER , $MSSQLDBNAME , $MSSSQLUSER ,$MSSQLPASS to container when running docker compose

  • Create gitlab ci/cd variables corresponding to $MSSQLSERVER , $MSSQLDBNAME , $MSSSQLUSER ,$MSSQLPASS
  • echo variables to .env file
deploy:
  stage: deploy
  before_script:
    - chmod 400 $SSH_KEY
  script:
    - ssh to deploy server "
        docker login ... && do something to pull source code including docker-compose.yml , .env &&
        echo "MSSQLPASS=$MSSQLPASS" >> .env && echo others $ && docker-compose down &&
        docker-compose up -d"

But it doesn’t work also, app complains that it cannot connect to sql server althought I can verify that information is correct and container has environment variables imported (I checked with export command)

Please give me some advice thank you very much.

2

I found the solution: use sed command to find and replace enviroment variables in (fake)appsettings.json with gitlab ci/cd variables while building image

.gitlab-ci.yml
build_image:
  stage: build
  image: docker:20.10.9
  services:
    - docker:20.10.9-dind
  variables:
    DOCKER_TLS_CERTDIR: "/certs"
  before_script:
    - docker login -u $REGISTRY_USER -p $REGISTRY_PASS
  script:
    - docker build --build-arg MSSQLSERVER=$MSSQLSERVER --build-arg MSSQLDBNAME=$MSSQLDBNAME
      --build-arg MSSSQLUSER=$MSSSQLUSER --build-arg MSSQLPASS=$MSSQLPASS
      -f Dockerfile -t name:tag .

FROM mcr.microsoft.com/dotnet/core/sdk:2.2

WORKDIR /app
COPY ./ ./
# set env for appsettings json
ARG MSSQLSERVER=1 MSSQLDBNAME=1 MSSSQLUSER=1 MSSQLPASS=1
RUN sed -i "s/\$MSSQLSERVER/$MSSQLSERVER/g" ./appsettings.json && \
    sed -i "s/\$MSSQLDBNAME/$MSSQLDBNAME/g" ./appsettings.json && \
    sed -i "s/\$MSSSQLUSER/$MSSSQLUSER/g" ./appsettings.json && \
    sed -i "s/\$MSSQLPASS/$MSSQLPASS/g" ./appsettings.json