Docker setup: Allow to configure number of worker processes

deployment/docker/pretix.bash

@@ -3,9 +3,10 @@ cd /pretix/src
 export DJANGO_SETTINGS_MODULE=production_settings
 export DATA_DIR=/data/
 export HOME=/pretix
-export NUM_WORKERS=$((2 * $(nproc --all)))
 
 AUTOMIGRATE=${AUTOMIGRATE:-yes}
+NUM_WORKERS_DEFAULT=$((2 * $(nproc --all)))
+export NUM_WORKERS=${NUM_WORKERS:-$NUM_WORKERS_DEFAULT}
 
 if [ ! -d /data/logs ]; then
     mkdir /data/logs;

doc/admin/installation/docker_smallscale.rst

@@ -295,7 +295,9 @@ on one machine after each upgrade manually, otherwise multiple containers might
 database schema at the same time.
 
 To run only the ``pretix-web`` component of pretix as well as a nginx server serving static files, you
-can invoke the container with ``docker run … pretix/standalone:stable web`` (instead of ``all``).
+can invoke the container with ``docker run … pretix/standalone:stable web`` (instead of ``all``). You
+can adjust the number of ``gunicorn`` processes with the ``NUM_WORKERS`` environment variable (defaults to
+two times the number of CPUs detected).
 
 To run only ``pretix-worker``, you can run ``docker run … pretix/standalone:stable taskworker``. You can
 also pass arguments to limit the worker to specific queues or to change the number of concurrent task