Docker: add UWSGI_WORKERS and UWSGI_THREAD.

UWSGI_WORKERS specifies the number of process.
UWSGI_THREADS specifies the number of threads.

The Docker convention is to specify the whole configuration
through environment variables. While not done in SearXNG, these two
additional variables allows admins to skip uwsgi.ini

In additional, https://github.com/searxng/preview-environments starts Docker
without additional files through searxng-helm-chat.
Each instance consumes 1Go of RAM which is a lot especially when there are a
lot of instances / pull requests.

Dockerfile

@@ -15,7 +15,9 @@ ENV INSTANCE_NAME=searxng \
     MORTY_KEY= \
     MORTY_URL= \
     SEARXNG_SETTINGS_PATH=/etc/searxng/settings.yml \
-    UWSGI_SETTINGS_PATH=/etc/searxng/uwsgi.ini
+    UWSGI_SETTINGS_PATH=/etc/searxng/uwsgi.ini \
+    UWSGI_WORKERS=%k \
+    UWSGI_THREADS=4
 
 WORKDIR /usr/local/searxng
 

dockerfiles/uwsgi.ini

@@ -4,8 +4,12 @@ uid = searxng
 gid = searxng
 
 # Number of workers (usually CPU count)
-workers = %k
-threads = 4
+# default value: %k (= number of CPU core, see Dockerfile)
+workers = $(UWSGI_WORKERS)
+
+# Number of threads per worker
+# default value: 4 (see Dockerfile)
+threads = $(UWSGI_THREADS)
 
 # The right granted on the created socket
 chmod-socket = 666

docs/admin/installation-docker.rst

@@ -92,6 +92,9 @@ instance using `docker run <https://docs.docker.com/engine/reference/run/>`_:
                 searxng/searxng
    2f998.... # container's ID
 
+The environment variables UWSGI_WORKERS and UWSGI_THREADS overwrite the default
+number of UWSGI processes and UWSGI threads specified in `/etc/searxng/uwsgi.ini`.
+
 Open your WEB browser and visit the URL:
 
 .. code:: sh