Aled Sage created BROOKLYN-492:
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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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