diff --git a/backend/Dockerfile b/backend/Dockerfile
index eab332b..b9c58ae 100644
--- a/backend/Dockerfile
+++ b/backend/Dockerfile
@@ -1,7 +1,9 @@
 # Build context: repository root (docker compose: context ".", dockerfile backend/Dockerfile)
+# No Alpine images: on Jambotron staging VMs (kernel 6.18.55-virt) binaries from Alpine 3.24.3
+# (musl 1.2.6) die with "Bus error" — java survived, curl in the healthcheck did not (2026-11-05)
 
 # 1. Web client (Angular) — served by the backend from classpath:/static
-FROM node:22-alpine AS web
+FROM node:22-bookworm-slim AS web
 WORKDIR /web
 COPY frontend/package*.json ./
 RUN npm install --no-audit --no-fund
@@ -9,7 +11,7 @@ COPY frontend/ ./
 RUN npx ng build --configuration=production
 
 # 2. Backend
-FROM eclipse-temurin:21-jdk-alpine AS build
+FROM eclipse-temurin:21-jdk AS build
 WORKDIR /app
 COPY gradlew settings.gradle ./
 COPY gradle gradle
@@ -19,9 +21,9 @@ COPY --from=web /web/dist/frontend/browser backend/src/main/resources/static
 RUN chmod +x gradlew && ./gradlew :backend:bootJar --no-daemon -x test
 
 # 3. Runtime: not root; data in /app/data (volume)
-FROM eclipse-temurin:21-jre-alpine
-# own user: "mail" already exists in Alpine (uid 8, group 12) — addgroup mail fails
-RUN apk add --no-cache curl && addgroup -S -g 10001 app && adduser -S -u 10001 -G app app \
+FROM eclipse-temurin:21-jre
+# Ubuntu image, curl included; own user: "mail" already exists (uid 8)
+RUN groupadd -r -g 10001 app && useradd -r -u 10001 -g app -d /app -s /usr/sbin/nologin app \
     && mkdir -p /app/data/attachments /app/data/dkim-keys && chown -R app:app /app/data
 WORKDIR /app
 COPY --from=build /app/backend/build/libs/*.jar app.jar