new docker-based build

This replaces the previous Dockerfile, which was a single stage for
building and deployment.

The new one is a multi-stage build. Its "dev" target has the full
development environment; its "deploy" target is more slim. It supports
cross-compiled builds via BuildKit, eg to prepare a build suitable for
a Raspberry Pi:

docker buildx build --load --platform=linux/arm64/v8 --tag=moonfire-nvr --progress=plain --target=deploy -f docker/Dockerfile .

Coming next: updating the installation docs.

docker/Dockerfile

@@ -0,0 +1,71 @@
+# syntax=docker/dockerfile:1.2.1
+
+# See documentation here:
+# https://github.com/moby/buildkit/blob/master/frontend/dockerfile/docs/syntax.md
+
+# Moonfire NVR development environment, using the build platform.
+FROM --platform=$BUILDPLATFORM ubuntu:20.04 AS dev
+LABEL maintainer="slamb@slamb.org"
+ARG TARGETARCH
+ARG BUILDARCH
+ARG BUILD_UID=1000
+ARG BUILD_GID=1000
+LABEL maintainer="slamb@slamb.org"
+ENV LC_ALL=C.UTF-8
+COPY docker/dev.bash /
+RUN /dev.bash
+USER moonfire-nvr:moonfire-nvr
+WORKDIR /var/lib/moonfire-nvr
+CMD	[ "/bin/bash", "--login" ]
+
+# Build the webpack with node_modules and ui-dist outside the src dir.
+FROM dev AS build-webpack
+LABEL maintainer="slamb@slamb.org"
+RUN --mount=type=bind,target=/var/lib/moonfire-nvr/src,readonly \
+    ln -s src/package.json src/yarn.lock src/ui-src src/webpack . && \
+    yarn install && yarn build && rm -rf node_modules
+
+# Build the Rust components. Note that dev.sh set up an environment variable
+# in .buildrc that similarly changes the target dir path.
+FROM dev AS build-server
+LABEL maintainer="slamb@slamb.org"
+RUN --mount=type=bind,target=/var/lib/moonfire-nvr/src,readonly \
+    bash -c 'set -o xtrace && source ~/.buildrc && cd src && cargo test && cargo build --release'
+
+# Deployment environment, now in the target platform.
+FROM --platform=$TARGETPLATFORM ubuntu:20.04 AS deploy
+ARG DEPLOY_UID=10000
+ARG DEPLOY_GID=10000
+LABEL maintainer="slamb@slamb.org"
+ENV LC_ALL=C.UTF-8
+RUN export DEBIAN_FRONTEND=noninteractive && \
+    apt-get update && \
+    apt-get install --assume-yes --no-install-recommends \
+        ffmpeg \
+        libncurses6 \
+        libncursesw6 \
+        locales \
+        sudo \
+        sqlite3 \
+        tzdata \
+        vim-nox && \
+    apt-get clean && \
+    rm -rf /var/lib/apt/lists/* && \
+    groupadd \
+        --gid="${DEPLOY_GID}" \
+        moonfire-nvr && \
+    useradd \
+        --no-log-init \
+        --home-dir=/var/lib/moonfire-nvr \
+        --uid="${DEPLOY_UID}" \
+        --gid=moonfire-nvr \
+        --shell=/bin/bash \
+        --create-home \
+        moonfire-nvr && \
+    ln -s moonfire-nvr /usr/local/bin/nvr
+COPY --from=build-server /var/lib/moonfire-nvr/moonfire-nvr /usr/local/bin/moonfire-nvr
+COPY --from=build-webpack /var/lib/moonfire-nvr/ui-dist/* /usr/local/moonfire-nvr/ui
+
+USER moonfire-nvr:moonfire-nvr
+WORKDIR /var/lib/moonfire-nvr
+ENTRYPOINT [ "/usr/local/bin/moonfire-nvr" ]