====== Multiple Component Instances via Configuration ======
In OSGi it is really simple and straightforward to create a service. Services in OSGi are singletons by default.

But sometimes you need multiple instances of the same service just with different configurations. And luckily OSGi also supports this.

===== Implementation =====
Just write your DS component as always as you would for a single instance component. Now add 

  configuration-policy="require"

to the component xml (or add it via annotations. I am a bit old school and still write the xml =). That means that a component will only be activated if there is a configuration for it.

You don't need to implement //ManagedService// for getting the configuration. So you can skip this step in your coding habit ;-).

===== Configuration =====
Here comes the tricky part. The normal configuration (always using //file install// for picking up the configuration) has the filename like the //service.pid// attribute with the suffix //cfg//. But that would mean that we would create a normal configuration ... and we wouldn't get multiple instances.

You syntax for the configuration file for multiple instances of a component (when using //file install//)is

  <component.name>-<new_service_pid>.cfg

The configuration file itself doesn't need the //service.pid// entry.

===== Configuration Modification =====
And if a configuration changes the component will be deactivated, deregistered and removed and a new component instance will be created with the updated configuration.

{{tag>osgi}}