[Important Notice] Changes in upgrade procedure for LeoFS 1.4

[Vladimir Mosgalin]

Dear LeoFS users,

Next LeoFS version - tentatively 1.4.0, but in case 1.3.8 will be released,
these changes will be there as well - has certain changes in official Linux
packages, requiring existing users to do some extra steps during upgrade
from older versions. This email serves as heads-up notice, to prepare users
beforehand.

For users of EL6 and EL7-based systems. Only single version of "leofs"
package can be installed at once from now on. Do not try to install new
version in parallel to the old one, upgrade to the new one using
"rpm -F" / "rpm -U" instead.

For users of systemd-based systems (EL7-based, Ubuntu 16.04). Before
upgrading package to the new version, users must stop existing LeoFS node(s)
on that host AND kill the instance of "epmd" process (please note that
killing "epmd" will disrupt any Erlang software running on that host, so it
should be done only after stopping LeoFS node and other Erlang software).
This is only required once (for upgrade from pre-1.4.0 to 1.4.0 and higher).
More details are available at
http://leo-project.net/leofs/docs/admin/system_admin/migration/#changes-in-leofs-packages-140

In case 1.3.8 will be released, then this migration information will apply to
upgrade from pre-1.3.8 to 1.3.8 and higher instead.


This upgrade procedure might be somewhat inconvenient, but these changes
allowed us to provide features that can make system administration of these
new versions much nicer:

- existence of /usr/local/leofs/current symlink (available on Linux systems
  which use official packages), which points to currently installed version,
  so that users can always execute
  "/usr/local/leofs/current/leo_gateway/bin/leo_gateway start", for example

- integration with systemd - users of systemd-based distributions
  (EL7-based, Ubuntu 16.04) can launch any kind of LeoFS nodes as systemd
  services, which allows automatic startup / shutdown of nodes on boot,
  reliable control of node state, automatic restart and other niceties. More
  information is available at
  http://leo-project.net/leofs/docs/admin/system_operations/systemd/

- Configuration in /etc/leofs, persistent between version upgrades. This is
  disabled by default for compatibility reasons, but can be enabled and used
  on any system. More information is available at
  http://leo-project.net/leofs/docs/admin/system_admin/persistent_configuration/
  With correct setup, it can allow upgrading to new versions as simple as
  installing new package and restarting currently running node.

- Ability to launch and control multiple nodes of the same type running on
  the same system - for example, it's useful for users who want to run
  multiple LeoFS clusters sharing same hardware. This feature requires
  running nodes as systemd services and using configuration from /etc/leofs.
  More information is available at
  http://leo-project.net/leofs/docs/admin/system_admin/multiple_nodes/
 
Feel free to ask me any questions regarding these changes in this list.

--
Vladimir

[yoshiyuki kanno]

Hello everyone,

Since we've decided to ship 1.3.8 before going to 1.4 series, this
change will be applied to 1.3.8 as Vladimir notified on the prev mail.

Best,
Kanno.

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--
Yoshiyuki Kanno
LeoFS Committer(http://leo-project.net/leofs/index.html)