In declarative services, one can set component(service) configuration policy to "REQUIRE", to make it dependent to existence of a certain config file. that means the service will not be created until the configuration with the matching "pid" is available in config admin.
Is there a similar solution in blueprint?
I have tried the managed-service-factory, but since I need only ONE instance of my service, I don't know how to make sure the factory only creates one instance.
I've been searching for an answer to this myself, and found nothing except this (very old) question!).
My solution is to
create a dummy declarative service with configurationPolicy=REQUIRE
declare a <reference ...'/> to this dummy service in blueprint (making blueprint wait until my dummy service is started.
In this way blueprint doesn't complete its startup until the relevant configuration exists. It feels like a bit of hack, and registers a pointless service.
Related
I have two osgi service which implements the same interface with a different quality-of-service. One has a default ranking of 0 and the other one has a ranking of 3.
I am searching for a blueprint configuration where the default service acts as a fallback. So every other bundle should use the best available service (highest ranking) and must fallback to the default one if the better service disappears.
That is working right now.
The missing part is to automatically reconnect to the better service, when it comes online again. Is there a way to do it by configuring just the services without changing the consumers (implement ServiceTrackers an so on)?
Declarative Services supports this with the greedy policy option. I don't know that it is possible in Blueprint.
I think this is not directly possible as a simple blueprint <reference>.
You can use the <reference-listener> element though.
<reference-listener bind-method=”bind” unbind-method=”unbind”>
<bean class=“MyListenerClass”/>
</reference-listener>
It allows to be called back when references change and react on these. So you can for example create a proxy for your service that makes sure the right service is called. This is not very pretty code though. So like BJ suggested declarative services may provide a cleaner solution for this case.
Rather than manually making configuration changes to OSGi components in Felix, it's good practice to create sling:OsgiConfig nodes in the JCR to make sure that the settings are version controlled, applied the same across environments, etc.
Similarly, I want to disable an out-of-the-box component on each environment. Is there any way to achieve this via configuration? Rather than going to system/console/components and disabling it there?
Anything I've read about this has mentioned making changes internally within the bundle, but since it's one that I don't own, I'd need some external configuration to do this.
You can do this with the ScrService, which is published by the SCR runtime bundle. API documentation is here.
Note that ScrService is not "standard", i.e. it doesn't come from the OSGi specification. However it is supported by Felix and Equinox and Knopflerfish, so it's pretty much a de facto standard. In fact this service is used by the Web Console when you go to system/console/components.
Try to use attribute policy=ConfigurationPolicy.REQUIRE on #Component.
Then you could prepare a set of packages with configurations for each environment as part of the build. This is also a good practice for having different OSGI configurations for each environment.
So for some of enironments you could just simply not provide a configuration for a particular component. Such component would not run - it would have unsatisfied status.
I believe I've seen this approach in AEM itself.
You can also create a filter to remove current configurations but it still would require to disable the Component at least once. And this solution will work only if this component has mentioned policy.
The other way around is to prepare a Service that would be responsible for disabling other components - it could be configurable. But it doesn't sound like a good solution to me.
I'd like to create a Configuration object in OSGi, but one that won't be persisted, so it won't be there when the framework is restarted. Similar to START_TRANSIENT for bundles.
Some background: I've got an OSGi (Felix) based client side application, deployed over OBR. The configuration object I'm talking about effectively boots the application. That works fine, but sometimes the content has changed while the context was stopped. In that case, it boots the application as OSGi revives all bundles and adds all configuration options. Then I inject the correct configuration, the application stops and then restarts again.
So it does actually work, but the app starts twice, and I can't get access to the framework before it reconstructs its old state.
Any ideas?
As BJ said there is no standard support for this in the Configuration Admin spec.
However the Felix implementation supports two features which may help you. First, you can set the felix.cm.dir property which configures where the configadmin saves its internal state (which by default will be somewhere under the Framework storage directory). You could set this to a location that you control and then simply wipe it every time you start OSGi (you could also wipe out the entire OSGi Framework storage directory on every start... some people do this but it has wider consequences that what you asked for).
Second, if you need a bit more control, Felix ConfigAdmin supports customising its persistence with a PersistenceManager service. You could probably implement this and return empty/doesn't-exist for the particular pids that you want to control.
The OSGi Config Admin spec does not support this. I also do not know of a non-standard means either for any of the CM impls I am familiar with.
Ok, what I did in the end was the following:
I created a special really small 'boot' bundle, which I do not provision from OBR, instead, I install it from the classpath.
That bundle controls the configuration, and I use START_TRANSIENT the moment I really want to load that configuration.
Not exactly pretty, it gets the job done. I do think transient configuration would make sense to have in OSGi.
I have a dynamic application that uses OSGi to load modular functionality at runtime. OSGi bundles contain the modular functionality and the application loads the bundles when they are needed. This approach works okay, but I would like a more granular solution. The bundles contain components controlled through Declarative Services. I'd like to be able to load a bundle, and only enable the components that are needed within the bundle. I've done research in this area, but cannot find a solution that I'm satisfied with. One approach was to create a "gatekeeper" component that is always enabled in the bundle and through the ComponentContext let it call enable and disable component. It's a viable solution, but I could not figure out a way for the "gatekeeper" to "know about" the other components in the bundle without hard coding the component names as properties in the "gatekeepers" SCR xml descriptor.
What I prefer is a way to load bundles and "know about" all components within the loaded bundles. Be able to determine what bundle the components are located in and what state they are currently in (similar to the equinox console command 'ls' that lists out all components). I would like to enable and disable the components when needed.
How does the console do this and how could I do this in an application?
Update:
#Neil Bartlett: Sorry for the delay. I had to move on to something else. Now I'm back on this issue. Really would appreciate any further assistance. My application is role based. I need to enable components based on the functionality they provide. The goal is for all role based components to initially be disabled. Upon role change, a role manager polls each component for its provided functionality and determines whether to load it. Each component will broadcast what functionality it provides (through a common service interface). ScrService will not allow me to enable an initially disabled service component. Having the components initially enabled and let ScrService disable them as soon as possible during application startup does not fit my needs.
Have a look at ScrService. Bothe equinox and felix has it.
However, components can be made to load lazily, i.e. only when needed by other components/bundles; but that is perhaps not what you want.
In your service description, mark the components as enabled, but requiring configuration information provided by the Configuration Management service. you then can write a CM plugin service (can't remember the exact term) that can publish and modify the configuration of your components. Services by default are identified by their name, which by default is their implementation class name. Configuration data is passed as a map, and it can be empty. DS will make the service available as soon as the CM provides a configuration.
I have a similar issue, but for a different purpose:
- I have apache file install and configuration admin service to configure my components externally with property files.
- I needed to make sure that some components get the config from the outer file and the only way I've found so far is that I mark my components with ConfigurationPolicy.REQUIRED.
- But that way my plugin projects doesn't run in eclipse (where there are no config files).
- The component.xml also contains a default development configuration so I'm okay with that, just my component doesn't start until there is a config data avalilable with configadmin. My components ar unsatisfied this way, until someone creates a configadmin entry.
- I figured out that if I create a osgi command line extender that sends empty configurations to service pid's they would start up with default values in component.xml files.
- I just came here to find a way to list all bundles
But I think this solution I use can also work with your setup and that's why I write this.
Just mark all your components with the configurtationpolicy.require and you can selectively start and stop them with adding and removing configurations with configadmin. This could be hard if you already use the configadmin for other purposes too, but it may be managable as a last resort.
Search did not give me a hint, how can i behave with the following situation:
I'd love to have 2 OSGI implementations of the same interface: one is regular, the other should work (be active/present/whatever) on the given time period (f.e for Christmas weeks :))
The main goal is to call the same interface without specifying any flags/properties/without manual switching of ranking. Application should somehow switch implementation for this special period, doing another/regular job before and after :)
I'm a newbie, maybe i do not completely understand OSGI concept somewhere, sorry for that of give me a hint or link, sorry for my English.
Using Felix/Equinox with Apache Aries.
The publisher of a service can register and unregister that service whenever it likes using the normal API. If it chooses then it can do so according to some regular schedule.
If there is another service instance that is available continuously, then the consumer of the service will sometimes see two instances of the service and sometimes see one. When there is only one instance available then it is trivial to get only that instance. When there are two instances then you need a way to ensure you get your "preferred" instance. The SERVICE_RANKING property is a way to do this. The getService method of a normal ServiceTracker will always return the higher ranked service, so this would appear to satisfy your requirement.
I have yet to see an OSGI container that at a framework level supports date/time based availability of services.
If I were you I would simply drop a proxy service in front of the two interface implementations and put the service invocation based on date logic in there.
I don't believe there is any framework support for what you are asking for.
If you are intent on avoiding service filters, you might try this.
Implement a PolicyService. This service is in charge of deciding which instance of your service should be registered at a given point in time. When its time for the policy service to switch implementations, it just uses the register/unregister apis as usual. You policy service implementation can read in a config file that specifies the date range to service implementation mapping. This will allow you to add new behavior by modifying your config file and installing a new bundle with the new service.
I agree with Neil that a service should only publish itself if it can actually be invoked. My solution to this problem would be to have all service producers be dependent on a "time constraint dependency". Whilst such a dependency is not available in the standard dependency frameworks (like Declarative Services, Blueprint, iPOJO) it is easily implemented with the Apache Felix Dependency Manager, which allows you to create your own types of dependencies. Note that writing such a new dependency once is some work, but if this is a core piece of your application I think it's worth it. Service consumers would not require any special logic, they would simply invoke the service that was there.
Ok, what i have finally done...
Implemented a common dispatcher bundle - and call any of services only thru it (therefore cron is not needed, when call is on-demand)
When dispatcher obtains request - it searches for interface in its own cache and -
When there are >1 service with the same ranking and both are equal (registered) - then
Dispatcher resolves needed service via own written #TimigPolicy annotation with "from" and "to" fields
For the given server new datetime() - dispatcher returns proper service instance
Much work, i should say :) But works nearly perfect :)
Thanks everybody for giving me hints, it was really helpful!!!