Upgrade to Mongo 3.6

[hwillson]

Hi all - this PR reverts the revert (85d74f8) of dfc0702, and includes fixes to address the previous test failures. I've labelled this as a work in progress, as I think it makes sense to also address the following issues, in this PR:

• New $v field in Mongo 3.6 oplog breaks OplogObserveDriver #9623 Done (8a5c2e4)
• [1.6.2-beta.3] Meteor can't start Mongo server after switching mongo versions  #9591 Done (75bd950)

The tests will of course fail here until a new dev_bundle is generated / published, but we can hold off on that until the above items are addressed.

I'll re-cap the previous Mongo 3.6 PR notes (#9533), so we don't have to jump around:

Fixes #9623.

---

This PR updates the Meteor Tool to use Mongo 3.6.2 for 64-bit OS' and Mongo 3.2.18 for 32-bit OS' (I've left the garbage BUNDLE_VERSION in place intentionally, since these changes will require a new dev_bundle publish from MDG).

A few important mentions:

• As of Mongo 3.6, all Mongo binary downloads include SSL - there is no longer a non-SSL based download bundle (so it's a bit bigger, but that shouldn't be an issue).
• Using the --nojournal option with WiredTiger based replica sets is no longer supported (see https://jira.mongodb.org/browse/SERVER-30760). The --nojournal flag was added in bcfe072 to help reduce the amount of disk space used by Mongo, but since this option is no longer supported, we'll have to live with the extra disk space usage.

Mongo Node driver side note:

The Mongo Node driver has recently jumped into the 3.x range, and has introduced a few breaking changes. While we normally bump the Mongo Node driver to the most recent version when doing Mongo updates, I've left it in 2.x range for now. I'll submit a separate Mongo Node driver 3.x update PR, so we can keep the focus on the Mongo upgrade here. Mongo 3.6 will work with 2.x versions of the Mongo Node driver.

Thanks!

[abernix]

It may be worth clarifying that, while Windows and Mac do only come bundled with SSL, SSL is still not included with the Generic Linux tarball (which scripts/generate-dev-bundle.sh pulls in), presumably since cross-distro linking of SSL libraries is more difficult. I snuck this change which accommodates that rule into the last PR, in order to build the dev bundle: fce09ac#diff-be3b40b6bc1b45a60ad8698bc2065cb9R57.

I've built the dev bundle, though we'll want to remember to quell e73013b before merging (as notated with the [DELETEME] prefix to the commit message).

Thanks for looking at this, @hwillson!

[hwillson]

The last part of this PR is to figure out what to do about #9591. When meteor update'ing to a version of the Tool that uses Mongo 3.6, jumping back to run an older version of Meteor (using meteor --release X) can break. This happens as the Mongo 3.6 updated database is no longer directly usable by Mongo 3.4 (or earlier). Why is the database no longer directly usable? Good question - I haven't been able to track the reason down (nothing in the logs, everything looks okay with the database, etc.). This might be caused by the fact that the Mongo 3.6 database is updated to use journaling by default, then we're jumping back to a setup that expects no journaling, but my tests in this area don't point to this being a problem.

The database can be repaired (see #9591 (comment)) and used with previous versions of Meteor, but this is a manual step. We can't really automate this as we'd then have to release new patch versions for older Meteor releases, to include the code to handle the database repair when the Mongo startup error happens. Due to the way Tool springboarding works, we can't just add code to handle the repair in Meteor 1.6.2, and expect to have it called when running meteor --release X. Given this, the best option here might just be to document this potential issue, as well as the mongod --repair fix, and make sure people are aware of the potential issue.

[hwillson]

Just re-capping the decision from our call - I'll document the potential issue mentioned in #9632 (comment), along with the Mongo repair fix, in the History.md. We should then be all set to get this merged. Updates coming shortly - thanks!

[hwillson]

This should now be ready for a new dev_bundle build/deploy (removing WIP). Thanks!

[abernix]

@hwillson I've re-published dev bundle 9999.9632.1 and the non-Windows tests passed, but I've just fixed the "merge conflict" so that AppVeyor will run.

[abernix]

Merged to devel as 3903020.

[bjarketrux]

Mongo 3.6 will work with 2.x versions of the Mongo Node driver.

Note: According to this page Node.js Driver Compatibility MongoDB 3.6 is only compatible with Node.js Driver >= 3.0.

I havn't investigated further.

[glasser]

@bjarketrux I believe that this means that not all features of MongoDB 3.6 are supported by the 2.x driver, but it doesn't like completely break.