Changes/Erlang 20

Erlang 20

Summary

Update Erlang/OTP to version 20.

Owner

• Name: Peter Lemenkov, Fedora Erlang SIG, Randy Barlow, Jeremy Cline
• Email: lemenkov@gmail.com, erlang@lists.fedoraproject.org, bowlofeggs@fedoraproject.org, jcline@fedoraproject.org
• Release notes ticket: #78

Current status

• Targeted release: Fedora 28
• Last updated: 2017-11-21
• Tracker bug: #1520901

Detailed Description

Upgrade Erlang to version 20 which brings a lot of good stuff. Just a few highlights:

• So-called dirty schedulers are available on systems with SMP.
• Atoms may now contain arbitrary Unicode characters (for example, 'здравствуй-你好').
• Erlang application can handle some OS signals (SIGHUP, for example).
• Improved unicode support for strings
• The zlib module has been refactored and all its operations will now yield appropriately, allowing them to be used freely in concurrent applications.

Aside from this, we plan to improve quality of Erlang and related packages. These are shortcomings we want to address:

• Every daemon written in Erlang has its own logging solution which doesn't use neither syslog nor Journald. We should start switching them to Journald.
• We should add ability to use D-Bus via erlang-dbus library.
• Further improve Erlang Packaging Guidelines.
• Start building noarch Erlang packages we've implemented previously.

Benefit to Fedora

Fedora users, both developers and end-users, will have visible benefits from using Fedora-provided packages. Namely:

• Even faster and smoother scheduling in Erlang. User's NIFs will work with less latency and smaller jitter.
• Improved logging, better unified with the rest of system.

Scope

• Proposal owners:
  • Upgrade Erlang to the latest version (20.2.3).. Done!
  • We must rebuild every package which requires NIF version (listed below in the Dependencies section) against Erlang 20.x.y.
  • Every Erlang daemon's systemd unit must require epmd.socket.
  • We need to fill new review request for erlang-ejournald
    • We have to fill new review request for erlang-lager_journald_backend
  • We need to fill new review request for erlang-dbus
  • Upgrade outdated packages:
    • Riak
      • Riak has has been retired. We have to re-add it back.
    • Ejabberd
  • Package rebar3 in a separate package and provide/adjust RPM macros.
  • Package GDB macros for easier coredump debugging (see also this ticket).
  • Enable Kerberos authentication in Ejabberd (finally).
• Other developers: N/A
• Release engineering: #7179
• Policies and guidelines:
  • We should promote officially Erlang Packaging Guidelines.
• Trademark approval: N/A (not needed for this Change)

Upgrade/compatibility impact

• Every Erlang upgrade requires the rebuilding of modules which contains ports or NIFs, and we will rebuild all such modules in Fedora. However if a user has some additional modules not available in a Fedora repository, then these modules must be rebuilt manually.
• Due to new atom's internal representation, some applications won't be able to deserialize data back serialized using previous Erlang version. The same applies to clustered applications - better upgrade and restart them entirely rather than adding a new upgraded nodes into a cluster.

How To Test

• Ensure that high-grade Erlang applications are still working:

Name	Tested
couchdb	No
ejabberd	No
elixir	No
mochiweb	No
rabbitmq-server	No
riak	No (package was retired :( )
wings	No

• Collect feedback from volunteers regarding their experience with this Erlang/OTP version

User Experience

Users will get more robust, scalable, and fast Erlang applications.

Dependencies

The following packages must be rebuilt:

Name	Rebuilt
couchdb	No
erlang-basho_metrics	Yes
erlang-bitcask	No
erlang-cache_tab	No
erlang-cl	No
erlang-ebloom	Yes
erlang-eleveldb	No
erlang-emmap	Yes
erlang-esip	No
erlang-fast_tls	No
erlang-fast_xml	No
erlang-fast_yaml	No
erlang-hyper	No
erlang-iconv	No
erlang-jiffy	Yes
erlang-riak_ensemble	No
erlang-sd_notify	Yes
erlang-skerl	Yes
erlang-snappy	Yes
erlang-stringprep	No
erlang-xmpp	No

Contingency Plan

• Contingency mechanism: None necessary. Instead of falling back to the previous version we should fix existing packages in order to help the Community. We should also monitor upstream development process for potentially discovered issues and proactively apply patches (as we already did with Erlang R14, Erlang R15, Erlang R16, Erlang 17), Erlang 18, and Erlang 19. It should be noted that this change consists from an independent or loosely coupled smaller changes. If we fail to deliver some changes in time, we should reschedule these exact changes to the future Fedora release while keeping already implemented ones.
• Contingency deadline: N/A
• Blocks release? N/A
• Blocks product? N/A

Documentation

• Erlang/OTP 20.0 release notes
• Erlang/OTP 20.1 release notes
• Erlang/OTP 20.2 release notes

Release Notes

Erlang/OTP 20.2.3 is available in Fedora 28.