feat(docker): add env var substitution for nginx config at runtime

install gettext package via apk to get envsubst tool
update docker-entrypoint.sh to export APP_ENV and APP_VERSION, then substitute these variables into the nginx configuration file before executing the main command

Dockerfile

@@ -17,7 +17,7 @@ LABEL org.opencontainers.image.created="${BUILD_DATE}"
 LABEL org.opencontainers.image.revision="${GIT_COMMIT}"
 LABEL org.opencontainers.image.source="https://git.kubistudio.cloud/kubistudio/cicd-multi-env-pipeline-poc"
 
-RUN apk add --no-cache curl
+RUN apk add --no-cache curl gettext
 
 COPY nginx.conf /etc/nginx/nginx.conf
 COPY src/ /usr/share/nginx/html/

docker-entrypoint.sh

@@ -21,4 +21,9 @@ window.__ENV__ = {
 };
 EOF
 
+export APP_ENV APP_VERSION
+
+envsubst '${APP_ENV} ${APP_VERSION}' < /etc/nginx/nginx.conf > /etc/nginx/nginx.conf.tmp
+mv /etc/nginx/nginx.conf.tmp /etc/nginx/nginx.conf
+
 exec "$@"