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From "Aled Sage (JIRA)" <j...@apache.org>
Subject [jira] [Created] (BROOKLYN-492) Brooklyn upgrade tricky if using `brooklyn.libraries` for custom OSGi bundles
Date Tue, 25 Apr 2017 21:30:04 GMT
Aled Sage created BROOKLYN-492:
----------------------------------

             Summary: Brooklyn upgrade tricky if using `brooklyn.libraries` for custom OSGi
bundles
                 Key: BROOKLYN-492
                 URL: https://issues.apache.org/jira/browse/BROOKLYN-492
             Project: Brooklyn
          Issue Type: Bug
            Reporter: Aled Sage


When a user refers to their custom OSGi bundle in a catalog's {{brooklyn.libraries}} section,
this could make subsequent upgrade of Brooklyn more difficult.

This is separate from Alex's email thread to dev@brooklyn "Making blueprint upgrades easier
- feature proposal" (i.e. it would not be solved by Alex's proposal). However, it's worth
thinking about that as well for a long-term holistic solution.

---
Consider the following steps:
* With Brooklyn 0.11.0:
  * A user writes a custom OSGi bundle (e.g. containing their own custom policy or Java entity
or whatever), compiled against Brooklyn 0.11.0.
  * The user creates a catalog item (v1.0), which references that bundle.
  * The user deploys some apps that use this catalog item (with their state being persisted).
* When Brooklyn 0.12.0 comes out, the user attempts to upgrade:
  * The user tries to start 0.12.0, rebinding against their existing persisted state. This
reads the catalog, and thus attempts to install/active the user's custom OSGi bundle.
  * Their custom bundle may fail to install (e.g. perhaps there are wiring errors due to dependency
changes between 0.11.0 and 0.12.0);
    or alternatively perhaps the bundle loads, but the instances of the Java policy/entity
fail to be instantiated (e.g. 0.11.0 and 0.12.0 are not binary compatible, with the user's
code relying on some class/method that has changed).
  * Rebind therefore might fails.
* The user tries to update their custom OSGi bundle:
  * The user updates their code and recompiles, to create a v2.0 of their bundle and of their
catalog item.
  * However, they can't start 0.12.0 with the existing persisted state in order to add the
v2.0 catalog item, and upgrade their entities.
  * The user might then try starting 0.11.0 up instead, and adding v2.0 of the catalog item
there.  
    This might work, or it might lead to bundle wiring errors because v2.0 is incompatible
with Brooklyn 0.11.0.

How likely this is to actually impact a user depends on: 1) what binary incompatible changes
we might make in Brooklyn between versions; and 2) what parts of Brooklyn the user's Java
code makes use of. Some power-users do some pretty sophisticated things, digging into the
less frequented classes of Brooklyn that on first blush might not be considered part of our
"api"!

---
The long-term solution needs a lot more discussion on the dev@brooklyn mailing list.

However, it might well revolve around being able to start Brooklyn into a usable state, even
when some blueprints/entities have errors. This is important so that errors can be resolved,
and so that errors in some blueprints don't cause the entire server to become unusable.

This is particularly important for big companies using Brooklyn, where there is a separation
of teams: one team responsible for managing Brooklyn servers/upgrades, and other teams responsible
for writing blueprints / catalog items.

---
A short-term solution could involve using offline tools to transform the persisted state (e.g.
using something like {{bin/brooklyn copy-state ... --transformations ...}}).

Note that the {{copy-state}} commands are not readily available if one is using just the Karaf
distro of Brooklyn.

Also note that {{./bin/brooklyn launch --catalogAdd ...}} is also not available if using the
Karaf distro of Brooklyn.





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