feat: Celery worker concurrency setting

This allows the user to configure how many Celery workers are spawned
independently of how many CPUs there are in the system. The default is
to spawn as many workers as there are CPUs, which in some cases can
consume too many resources.

(The setting should be particularly useful to people running Tutor for
development on Linux machines, where reducing the concurrency to "1" can
reduce RAM usage significantly.)

Author: arbrandes

changelog.d/20240229_171657_arbrandes_celery_concurrency.md

@@ -0,0 +1 @@
+- [Feature] Allow the user to configure Celery worker concurrency. (by @arbrandes)

docs/configuration.rst

@@ -149,6 +149,11 @@ This defines the version that will be pulled from just the Open edX platform git
 
 By default, there are 2 `uwsgi worker processes <https://uwsgi-docs.readthedocs.io/en/latest/Options.html#processes>`__ to serve requests for the LMS and the CMS. However, each worker requires upwards of 500 Mb of RAM. You should reduce this value to 1 if your computer/server does not have enough memory.
 
+- ``OPENEDX_LMS_CELERY_WORKERS`` (default: ``"0"``)
+- ``OPENEDX_CMS_CELERY_WORKERS`` (default: ``"0"``)
+
+This sets the number of Celery workers at startup.  Defaults to the number of CPUs detected on the system (represented by "0").  If your system's RAM is limited, you may need to set this to a low integer value in order to conserve it.  (On development deployments, it is suggested to use "1" for both.)
+
 - ``OPENEDX_CELERY_REDIS_DB`` (default: ``0``)
 - ``OPENEDX_CACHE_REDIS_DB`` (default: ``1``)
 

tutor/templates/config/defaults.yml

@@ -54,7 +54,9 @@ OPENEDX_AWS_ACCESS_KEY: ""
 OPENEDX_AWS_SECRET_ACCESS_KEY: ""
 OPENEDX_CACHE_REDIS_DB: 1
 OPENEDX_CELERY_REDIS_DB: 0
+OPENEDX_CMS_CELERY_WORKERS: 0
 OPENEDX_CMS_UWSGI_WORKERS: 2
+OPENEDX_LMS_CELERY_WORKERS: 0
 OPENEDX_LMS_UWSGI_WORKERS: 2
 OPENEDX_MYSQL_DATABASE: "openedx"
 OPENEDX_MYSQL_USERNAME: "openedx"

tutor/templates/k8s/deployments.yml

@@ -141,7 +141,7 @@ spec:
       containers:
         - name: cms-worker
           image: {{ DOCKER_IMAGE_OPENEDX }}
-          args: ["celery", "--app=cms.celery", "worker", "--loglevel=info", "--hostname=edx.cms.core.default.%%h", "--max-tasks-per-child", "100", "--exclude-queues=edx.lms.core.default"]
+          args: ["celery", "--app=cms.celery", "worker", "--loglevel=info", "--hostname=edx.cms.core.default.%%h", "--concurrency={{ OPENEDX_CMS_CELERY_WORKERS }}", "--max-tasks-per-child", "100", "--exclude-queues=edx.lms.core.default"]
           env:
           - name: SERVICE_VARIANT
             value: cms
@@ -250,7 +250,7 @@ spec:
       containers:
         - name: lms-worker
           image: {{ DOCKER_IMAGE_OPENEDX }}
-          args: ["celery", "--app=lms.celery", "worker", "--loglevel=info", "--hostname=edx.lms.core.default.%%h", "--max-tasks-per-child=100", "--exclude-queues=edx.cms.core.default"]
+          args: ["celery", "--app=lms.celery", "worker", "--loglevel=info", "--hostname=edx.lms.core.default.%%h", "--concurrency={{ OPENEDX_LMS_CELERY_WORKERS }}", "--max-tasks-per-child=100", "--exclude-queues=edx.cms.core.default"]
           env:
           - name: SERVICE_VARIANT
             value: lms

tutor/templates/local/docker-compose.yml

@@ -158,7 +158,7 @@ services:
     environment:
       SERVICE_VARIANT: lms
       DJANGO_SETTINGS_MODULE: lms.envs.tutor.production
-    command: celery --app=lms.celery worker --loglevel=info --hostname=edx.lms.core.default.%%h --max-tasks-per-child=100 --exclude-queues=edx.cms.core.default
+    command: celery --app=lms.celery worker --loglevel=info --hostname=edx.lms.core.default.%%h --concurrency={{ OPENEDX_LMS_CELERY_WORKERS }} --max-tasks-per-child=100 --exclude-queues=edx.cms.core.default
     restart: unless-stopped
     volumes:
       - ../apps/openedx/settings/lms:/openedx/edx-platform/lms/envs/tutor:ro
@@ -177,7 +177,7 @@ services:
     environment:
       SERVICE_VARIANT: cms
       DJANGO_SETTINGS_MODULE: cms.envs.tutor.production
-    command: celery --app=cms.celery worker --loglevel=info --hostname=edx.cms.core.default.%%h --max-tasks-per-child 100 --exclude-queues=edx.lms.core.default
+    command: celery --app=cms.celery worker --loglevel=info --hostname=edx.cms.core.default.%%h --concurrency={{ OPENEDX_CMS_CELERY_WORKERS }} --max-tasks-per-child 100 --exclude-queues=edx.lms.core.default
     restart: unless-stopped
     volumes:
       - ../apps/openedx/settings/lms:/openedx/edx-platform/lms/envs/tutor:ro