Adjust Dockerfiles to speed up builds during development (#1992)

* Adjust Dockerfiles to speed up builds during development

* Improve comments to clarify the intention

install/docker/base

@@ -12,15 +12,16 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+# Do not add forseti source in this file to avoid rebuilding base during development.
+
 FROM ubuntu:18.04
 
-# Expose our source so we can read in dependencies.
-ADD . /forseti-security/
-WORKDIR /forseti-security/
+# Add the apt dependencies
+ADD install/dependencies/apt_packages.txt /tmp
 
 # Install host dependencies.
 RUN apt-get update -qq 1> /dev/null && \
-    apt-get install -qq -y $(cat install/dependencies/apt_packages.txt | grep -v "#" | xargs) 1> /dev/null && \
+    apt-get install -qq -y $(cat /tmp/apt_packages.txt | grep -v "#" | xargs) 1> /dev/null && \
     rm -rf /var/lib/apt/lists/*
 
 # Install the CloudSDK for `gcloud`.

install/docker/forseti

@@ -15,8 +15,8 @@
 ARG BASE_IMAGE=forseti/base
 FROM ${BASE_IMAGE}
 
-# Expose our source so we can install Forseti Security.
-ADD . /forseti-security/
+# Add pip requirements file
+ADD requirements.txt /forseti-security/
 WORKDIR /forseti-security/
 
 # Install Forseti Security dependencies.
@@ -27,5 +27,8 @@ RUN pip install -q --upgrade pip==9.0.3
 RUN pip install -q --upgrade setuptools wheel 1> /dev/null
 RUN pip install -q --upgrade -r requirements.txt 1> /dev/null
 
+# Expose our source so we can install Forseti Security.
+ADD . /forseti-security/
+
 # Install Forseti Security.
 RUN python setup.py install 1> /dev/null