Add template for building Python 3 chutes.

paradrop/daemon/paradrop/core/container/templates/Dockerfile-python2.txt

@@ -1,7 +1,7 @@
 FROM {image}
 
 # Set up an unprivileged user so that we can drop out of root.
-# Make /home/paradrop so that npm can drop some files in there.
+# Make /home/paradrop so that tools can drop some files in there.
 # Make /opt/paradrop/app for installing the app files.
 RUN useradd --system --uid 999 paradrop && \
     mkdir -p /home/paradrop && \

paradrop/daemon/paradrop/core/container/templates/Dockerfile-python3.txt

@@ -0,0 +1,40 @@
+FROM {image}
+
+# Set up an unprivileged user so that we can drop out of root.
+# Make /home/paradrop so that tools can drop some files in there.
+# Make /opt/paradrop/app for installing the app files.
+RUN useradd --system --uid 999 paradrop && \
+    mkdir -p /home/paradrop && \
+    chown paradrop /home/paradrop && \
+    mkdir -p /opt/paradrop/app && \
+    chown paradrop /opt/paradrop/app && \
+    chmod a+s /opt/paradrop/app
+
+WORKDIR /opt/paradrop/app
+
+# Add cap_net_bind_service to node so that it can bind to ports 1-1024.
+# Not all images support this.
+RUN setcap 'cap_net_bind_service=+ep' /usr/local/bin/node || true
+
+# Install some useful tools and libraries.
+RUN apt-get update && \
+    apt-get install -y \
+        iptables
+
+{has_packages:if:RUN apt-get install -y {packages}}
+
+# Defang setuid/setgid binaries.
+RUN find / -perm +6000 -type f -exec chmod a-s {{}} \; || true
+
+# Copy paradrop.yaml and requirements.txt, the latter only if it exists.  These
+# layers will be cached as long as the requirements do not change.
+COPY paradrop.yaml requirements.tx[t] /opt/paradrop/app/
+RUN if [ -f requirements.txt ]; then pip install --requirement requirements.txt; fi
+
+# Now copy the rest of the files.
+COPY . /opt/paradrop/app/
+RUN chown paradrop:paradrop -R /opt/paradrop/app
+
+{drop_root:if:USER paradrop}
+
+CMD {cmd}