[CI] Improve Docker image caching by copying app code last (#36)

Author: Frenzie

.github/workflows/unit_tests.yaml

@@ -17,7 +17,16 @@ jobs:
         uses: docker/setup-buildx-action@v3
 
       - name: Build image
-        run: make build VERSION=test
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          push: false
+          load: true
+          tags: |
+            koreader/kosync:test
+            koreader/kosync:latest
+          cache-from: type=gha
+          cache-to: type=gha,mode=max
 
       - name: Run busted test suite
         run: make test VERSION=test

Dockerfile

@@ -10,7 +10,7 @@ RUN apt-get update \
     && apt-get clean && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
 
 ARG OPENRESTY_VER=1.27.1.2
-ENV PATH /opt/openresty/nginx/sbin:$PATH
+ENV PATH=/opt/openresty/nginx/sbin:$PATH
 
 WORKDIR /app
 RUN wget "https://openresty.org/download/openresty-${OPENRESTY_VER}.tar.gz" \
@@ -25,13 +25,13 @@ RUN mkdir -p /etc/nginx/ssl \
     && openssl req -x509 -nodes -days 365 -newkey rsa:2048 \
         -keyout /etc/nginx/ssl/nginx.key -out /etc/nginx/ssl/nginx.crt -subj "/"
 
-# add app source code
-COPY ./ koreader-sync-server
+# copy only the patch needed for the gin build step
+COPY gin.patch /tmp/gin.patch
 
 # patch gin for https support
 RUN git clone https://github.com/ostinelli/gin \
     && cd gin \
-    && patch -N -p1 < /app/koreader-sync-server/gin.patch \
+    && patch -N -p1 < /tmp/gin.patch \
     && luarocks make --tree=/usr/local \
     && cd .. \
     && rm -rf gin
@@ -59,6 +59,9 @@ RUN mkdir /etc/service/koreader-sync-server \
         /etc/service/koreader-sync-server/run \
     && chmod +x /etc/service/koreader-sync-server/run
 
+# add app source code last so app changes don't invalidate dependency layers
+COPY ./ koreader-sync-server
+
 VOLUME ["/var/log/redis", "/var/lib/redis"]
 
 EXPOSE 7200