Create gfortran container.

.gitlab-ci.yml

+---
+stages:
+  - docker
+  - build
+
+gfortran:
+  stage: docker
+  image:
+    name: gcr.io/kaniko-project/executor:debug
+    entrypoint: [""]
+  rules:
+    - changes:
+        - Dockerfile
+        - build-container.sh
+  tags: [docker]
+  script:
+    - ./build-container.sh

Dockerfile

+FROM alpine
+
+RUN apk add gfortran-10

build-container.sh

+#!/busybox/sh
+
+mkdir -p /kaniko/.docker
+printf '{"auths":{"%s":{"username":"%s","password":"%s"}}}' \
+       "$CI_REGISTRY" "$CI_REGISTRY_USER" "$CI_REGISTRY_PASSWORD" \
+       > /kaniko/.docker/config.json
+
+container=registry.ie.suberic.net/kevin/bulletin/gfortran:latest
+echo "================= Building $container"
+/kaniko/executor \
+      --cache=true \
+      --context "$PWD" \
+      --dockerfile "$PWD/Dockerfile" \
+      --destination "$container" || exit 1