synapse-workers docker: copy nginx and redis in from base images (#13447)

Part of my continuing quest to make the docker images build quicker: copy nginx and redis in from base docker images, rather than apt installing each time.

changelog.d/13447.misc

@@ -0,0 +1 @@
+Improve rebuild speed for the "synapse-workers" docker image.

docker/Dockerfile-workers

@@ -1,9 +1,12 @@
 # syntax=docker/dockerfile:1
-# Inherit from the official Synapse docker image
-ARG SYNAPSE_VERSION=latest
-FROM matrixdotorg/synapse:$SYNAPSE_VERSION
 
-# Install deps
+ARG SYNAPSE_VERSION=latest
+
+# first of all, we create a base image with an nginx which we can copy into the
+# target image. For repeated rebuilds, this is much faster than apt installing
+# each time.
+
+FROM debian:bullseye-slim AS deps_base
     RUN \
        --mount=type=cache,target=/var/cache/apt,sharing=locked \
        --mount=type=cache,target=/var/lib/apt,sharing=locked \
@@ -11,13 +14,33 @@ RUN \
       DEBIAN_FRONTEND=noninteractive apt-get install -yqq --no-install-recommends \
           redis-server nginx-light
 
+# Similarly, a base to copy the redis server from.
+#
+# The redis docker image has fewer dynamic libraries than the debian package,
+# which makes it much easier to copy (but we need to make sure we use an image
+# based on the same debian version as the synapse image, to make sure we get
+# the expected version of libc.
+FROM redis:6-bullseye AS redis_base
+
+# now build the final image, based on the the regular Synapse docker image
+FROM matrixdotorg/synapse:$SYNAPSE_VERSION
+
     # Install supervisord with pip instead of apt, to avoid installing a second
     # copy of python.
     RUN --mount=type=cache,target=/root/.cache/pip \
         pip install supervisor~=4.2
+    RUN mkdir -p /etc/supervisor/conf.d
 
-# Disable the default nginx sites
+    # Copy over redis and nginx
+    COPY --from=redis_base /usr/local/bin/redis-server /usr/local/bin
+
+    COPY --from=deps_base /usr/sbin/nginx /usr/sbin
+    COPY --from=deps_base /usr/share/nginx /usr/share/nginx
+    COPY --from=deps_base /usr/lib/nginx /usr/lib/nginx
+    COPY --from=deps_base /etc/nginx /etc/nginx
     RUN rm /etc/nginx/sites-enabled/default
+    RUN mkdir /var/log/nginx /var/lib/nginx
+    RUN chown www-data /var/log/nginx /var/lib/nginx
 
     # Copy Synapse worker, nginx and supervisord configuration template files
     COPY ./docker/conf-workers/* /conf/

docker/conf-workers/supervisord.conf.j2

@@ -19,7 +19,7 @@ username=www-data
 autorestart=true
 
 [program:redis]
-command=/usr/local/bin/prefix-log /usr/bin/redis-server /etc/redis/redis.conf --daemonize no
+command=/usr/local/bin/prefix-log /usr/local/bin/redis-server
 priority=1
 stdout_logfile=/dev/stdout
 stdout_logfile_maxbytes=0