GREYSimplify the updates of Magnolia instancesGREY
Rationale
Module updates and Magnolia updates are currently a little cumbersome; one needs to either rebuild their webapp, and move/copy lots of jar files. Making sure superfluous modules are removed and extra modules re-added can be tedious.
Other webapps have shown it possible since a while to have plugins downloaded from the internet right into the webapp and deployed automatically. In some cases, they don't even require a restart of the application in the application server.
Goals
- ease deployment, maintenance and updates of Magnolia modules
- faster spread of updates
- if modules are easily updated, the core of Magnolia and the bundling don't need to be updated as much, and the modules can really start flying at their own pace.
- (as a positive side-effect, we might be able to slim the main download's sizes)
Features / dependencies
In no particular order, here's a quick breakdown of independent features:
Magnolia.home
The Magnolia webapp should be markable as read-only; module jars should be loadable from outside the webapp folder (we don't want to(can not) write inside /WEB-INF/). Other files (repository, indexes, cache, ...) should also be written outside the webapp. See MAGNOLIA-2170@jira and the linked user-list thread for some background discussion.
This is independent of a library choice, but should be implemented prior to actual module download/upgrade. (we'll need to download the modules, extract bundles, ...)
MAGNOLIA-2170@jira
Split core
Magnolia-core will probably have to remain in the webapp folder: extract more out of core, so that it can also benefit from easy updates.
Hot (re)deploy
No need to restart the app/appserver to deploy a module update. ("updates are ready: [apply now, silently] or [click here for switching to the update UI when ready]"; alternatively, we could maybe make it so that the system still works while updates are being applied, and switches "atomically" at the end? - or at least provide a configurable temp page for public instances)
We can already restart a module. Missing points:
- restart this module's dependencies in the appropriate order. (restarting all is probably good enough)
- load modules in an isolated classloader, so hopefully, we can swap to the new jars once they're downloaded. We have some experience w/ classloaders, see magnolia-tools ! (+include classloader debug info in the diagnostics module !)
- what happens to the public site while updating (is Magnolia accessible, do we have a temp page)
Uninstall modules
Most of our modules are actually fairly easily uninstallable (see docu, it's mostly removing the jar and removing a few specific nodes), so this should be feasible. Provide backup of removed nodes for safety. Uninstalls could be "automatic" when a jar removal is detected (i.e when restarting the server) or done through some form of gui. Potential implementation would imply serializing the tasks-for-uninstalling at install time. (store result of ModuleVersionHandler.getUninstallTasks())
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System workspace
We're currently store the module related information in the configuration workspaces, in various places: current module version under /module/xyz/version
, backup of some config nodes under /server/install/backup
, information about extracted files under /server/install/mgnl-files
. We could instead use a specific workspace.
External libraries
Modules need to be bundled with 3rd party libs (e.g Quartz with the Scheduler module). Current limitation of our module system is that we don't provide any "check" - e.g Scheduler module bluntly fails to start after installation; thus blocking the complete system.
UI
Missing dependencies should be reported in the ui.
Security: the current update UI is totally open: provide a better/configurable page for public instances while updates are being performed. See MAGNOLIA-1629@jira.
Module descriptions
For download and install, we'll want to display decent module descriptions etc, maybe even screenshots. This implies we might need to add some features to the module descriptor.
Server side
Where and how we deploy and publish modules.
Versions, dependencies
Our current dependency system can state a minimal required version (i.e module X depends on Y 1.3 and up and on core 4.1 and up. Somehow, we'll have to be able to also say that module X 1.2 will not work anymore with Y 1.5, which is not something that we can determine when X is released. So this is probably something that needs to happen on the server-side of things.
Detecting inter-module dependencies
Handling of module's own dependencies (i.e non-Magnolia)
We can't detect them, but since our current build generates bundles including them, we could possibly do something about that. | Additionally, if the Maven team do the same work for other Maven components than what they've done for Mercury, there might be a simple and small API to read a module's pom, and thus derive the external dependencies from. | | | | |
Downloading artifacts
Existing implementations, libraries, ...
- Examples of existing implementations of such features: Confluence, Hudson, ...
- We could(should) also evaluate OSGi, although my feeling is that it is very complex and bulky, and will incur more cost than bring benefits. Somehow I hope I'm wrong.
- We might also want to evaluate how to re-use the Maven infrastructure. This might be particularly interesting since our builds already deploy to Maven repositories, we might not have to invent much as far as getting new modules goes ! The current effort is going into "Mercury", which as far as I understand, will be a foundation block for Maven 3:
- http://svn.magnolia-cms.com/svn/internal/testing-mercury/
- http://www.sonatype.com/people/2008/11/what-is-mercury/
- http://maven.apache.org/mercury/index.html
- http://docs.codehaus.org/display/MAVEN/Mercury
- http://docs.codehaus.org/display/MAVEN/HowTo+use+Mercury+for+accessing+repositories
- http://repo2.maven.org/maven2/org/apache/maven/mercury/ (1.0-alpha-5 is available at the time of writing)
- http://svn.eu.apache.org/viewvc/maven/mercury/trunk/