Add mongo read preference OPS-2440

[jdmulloy]

Configuration Pull Request

Make sure that the following steps are done before merging:

• A DevOps team member has approved the PR.
• Are you adding any new default values that need to be overridden when this change goes live? If so:
  • Update the appropriate internal repo (be sure to update for all our environments)
  • If you are updating a secure value rather than an internal one, file a DEVOPS ticket with details.
  • Add an entry to the CHANGELOG.
• If you are making a complicated change, have you performed the proper testing specified on the Ops Ansible Testing Checklist? Adding a new variable does not require the full list (although testing on a sandbox is a great idea to ensure it links with your downstream code changes).

[feanil]

Did you mean for this to be EDXAPP_MONGO_READ_PREFERENCE ?

[jdmulloy]

Yes

[mtyaka]

@jdmulloy After this change we're seeing our sandboxes fail with

/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 354, in execute_from_command_line
    utility.execute()
  File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 346, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/django/core/management/base.py", line 394, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/django/core/management/base.py", line 445, in execute
    output = self.handle(*args, **options)
  File "/edx/app/edxapp/edx-platform/cms/djangoapps/contentstore/management/commands/import.py", line 38, in handle
    mstore = modulestore()
  File "/edx/app/edxapp/edx-platform/common/lib/xmodule/xmodule/modulestore/django.py", line 333, in modulestore
    contentstore(),
  File "/edx/app/edxapp/edx-platform/common/lib/xmodule/xmodule/contentstore/django.py", line 28, in contentstore
    _CONTENTSTORE[name] = class_(**options)
  File "/edx/app/edxapp/edx-platform/common/lib/xmodule/xmodule/contentstore/mongo.py", line 42, in __init__
    port=port, tz_aware=tz_aware, user=user, password=password, proxy=proxy, **kwargs
  File "/edx/app/edxapp/edx-platform/common/lib/xmodule/xmodule/mongo_utils.py", line 42, in connect_to_mongodb
    **kwargs
  File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/pymongo/mongo_client.py", line 311, in __init__
    option, value = common.validate(option, value)
  File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/pymongo/common.py", line 446, in validate
    value = validator(option, value)
  File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/pymongo/common.py", line 243, in validate_read_preference
    raise ConfigurationError("Not a valid read preference")
pymongo.errors.ConfigurationError: Not a valid read preference

Any idea why?

[mtyaka]

Could it be because we are not using mongo replica sets for our sandboxes?

[mtyaka]

I opened a PR with a proposed fix at https://github.com/edx/edx-platform/pull/16540.

[feanil]

@mtyaka we've reverted this for now while we figure out what's going on and fix the PR.

[feanil]

Sorry for the inconvenience.