feat: switch to Alpine base image and update package installation method

Author: ChristophShyper

.dockerignore

@@ -6,4 +6,4 @@
 !LICENSE
 !README.md
 !entrypoint.sh
-!pip
+§!alpine-packages.txt

Dockerfile

@@ -2,25 +2,25 @@
 FROM devopsinfra/docker-terragrunt:slim-latest AS builder
 
 # Use a clean tiny image to store artifacts in
-FROM ubuntu:questing-20251217
-
-# Disable interactive mode
-ENV DEBIAN_FRONTEND=noninteractive
+FROM alpine:3.23.4
 
 # Copy all needed files
 COPY --from=builder /usr/bin/terraform /usr/bin/format-hcl /usr/bin/fmt.sh /usr/bin/terragrunt-fmt.sh /usr/bin/
 COPY entrypoint.sh /
+COPY alpine-packages.txt /tmp/alpine-packages.txt
 
 # Install needed packages
-SHELL ["/bin/bash", "-euxo", "pipefail", "-c"]
-# hadolint ignore=DL3008
-RUN set -eux ;\
-  apt-get update -y ;\
-  chmod +x /entrypoint.sh /usr/bin/format-hcl /usr/bin/fmt.sh /usr/bin/terragrunt-fmt.sh ;\
-  apt-get clean ;\
-  rm -rf /var/lib/apt/lists/*
+SHELL ["/bin/sh", "-euxo", "pipefail", "-c"]
+# hadolint ignore=DL3018
+RUN set -eux; \
+  xargs -r apk add --no-cache < /tmp/alpine-packages.txt; \
+  chmod +x /entrypoint.sh /usr/bin/terraform /usr/bin/format-hcl /usr/bin/fmt.sh /usr/bin/terragrunt-fmt.sh; \
+  terraform version; \
+  rm -rf /var/cache/*; \
+  rm -rf /root/.cache/*; \
+  rm -rf /tmp/*
 
 # Finish up
-CMD ["terraform --version"]
+CMD ["terraform", "version"]
 WORKDIR /github/workspace
 ENTRYPOINT ["/entrypoint.sh"]

alpine-packages.txt

@@ -0,0 +1 @@
+bash~=5.3

tests/docker/local-image.yml

@@ -4,7 +4,7 @@ commandTests:
   - name: OS version check
     command: cat
     args: [/etc/os-release]
-    expectedOutput: [VERSION_ID="25\.10"]
+    expectedOutput: [VERSION_ID=3\.23]
 
   - name: Required tools installed
     command: bash
@@ -31,11 +31,14 @@ commandTests:
           >/tmp/check-write.log 2>&1 || (cat /tmp/check-write.log && exit 1)
         grep -q 'check=true requires write=false; overriding write to false' /tmp/check-write.log
 
-  - name: Apt cache cleaned
+  - name: Temporary and APK cache cleaned
     command: bash
     args:
       - -lc
-      - test ! -d /var/lib/apt/lists || test -z "$(find /var/lib/apt/lists -mindepth 1 -maxdepth 1 2>/dev/null)"
+      - >-
+        test ! -f /tmp/alpine-packages.txt &&
+        (test ! -d /var/cache/apk || test -z "$(find /var/cache/apk -mindepth 1 -maxdepth 1 2>/dev/null)") &&
+        (test ! -d /root/.cache || test -z "$(find /root/.cache -mindepth 1 -maxdepth 1 2>/dev/null)")
 
 fileExistenceTests:
   - name: entrypoint exists