fix: Generate ssl certificates in builder image

docker/test/nginx/Dockerfile

@@ -1,16 +1,24 @@
+FROM alpine AS cert-builder
+
+RUN apk add --no-cache openssl
+
+# Generate certs during build
+RUN mkdir -p /tmp/ssl && \
+    openssl req -x509 -nodes -days 365 \
+      -newkey rsa:2048 \
+      -keyout /tmp/ssl/selfsigned.key \
+      -out /tmp/ssl/selfsigned.crt \
+      -subj "/CN=localhost"
+
 FROM nginx:mainline-alpine
 
 COPY nginx.conf /etc/nginx/nginx.conf
 COPY paths-enabled /etc/nginx/paths-enabled.d
 
-RUN mkdir -p /etc/nginx/ssl && \
-    openssl req -x509 -nodes -days 365 \
-      -newkey rsa:2048 \
-      -subj "/CN=localhost" \
-      -keyout /etc/nginx/ssl/selfsigned.key \
-      -out /etc/nginx/ssl/selfsigned.crt \
-COPY entrypoint.sh /entrypoint.sh
+COPY --from=cert-builder /tmp/ssl/selfsigned.crt /etc/nginx/ssl/selfsigned.crt
+COPY --from=cert-builder /tmp/ssl/selfsigned.key /etc/nginx/ssl/selfsigned.key
 
+COPY entrypoint.sh /entrypoint.sh
 RUN chmod +x /entrypoint.sh
 
 ENTRYPOINT ["/entrypoint.sh"]