Add an option to override max tasks pre child for edxapp workers.

Update default tasks per child for high mem queue.

playbooks/roles/edxapp/defaults/main.yml

@@ -425,6 +425,7 @@ EDXAPP_CELERY_WORKERS:
     service_variant: lms
     concurrency: 2
     monitor: False
+    max_tasks_per_child: 1
 
 EDXAPP_DEFAULT_CACHE_VERSION: "1"
 EDXAPP_OAUTH_ENFORCE_SECURE: True

playbooks/roles/edxapp/templates/workers.conf.j2

@@ -7,7 +7,7 @@ directory={{ edxapp_code_dir }}
 stdout_logfile={{ supervisor_log_dir }}/%(program_name)s-stdout.log
 stderr_logfile={{ supervisor_log_dir }}/%(program_name)s-stderr.log
 
-command={{ edxapp_venv_dir + '/bin/newrelic-admin run-program ' if w.monitor and COMMON_ENABLE_NEWRELIC else ''}}{{ edxapp_venv_bin }}/python {{ edxapp_code_dir }}/manage.py {{ w.service_variant }} --settings=aws celery worker --loglevel=info --queues=edx.{{ w.service_variant }}.core.{{ w.queue }} --hostname=edx.{{ w.service_variant }}.core.{{ w.queue }}.%%h --concurrency={{ w.concurrency }}
+command={{ edxapp_venv_dir + '/bin/newrelic-admin run-program ' if w.monitor and COMMON_ENABLE_NEWRELIC else ''}}{{ edxapp_venv_bin }}/python {{ edxapp_code_dir }}/manage.py {{ w.service_variant }} --settings=aws celery worker --loglevel=info --queues=edx.{{ w.service_variant }}.core.{{ w.queue }} --hostname=edx.{{ w.service_variant }}.core.{{ w.queue }}.%%h --concurrency={{ w.concurrency }} {{ '--maxtasksperchild ' + w.max_tasks_per_child|string if w.max_tasks_per_child is defined else '' }}
 killasgroup=true
 stopasgroup=true
 stopwaitsecs=432000