Added documentation for multi-tenancy

[pooja1pathak]

Updated https://github.com/Orange-OpenSource/fiware-cepheus/blob/master/doc/admin/cep.md to explain how to enable multi-tenancy feature.

Added multi-tenant.md, multi_01.png, multi_02.png and multi_03.png to explain how multi-tenancy works and how it relates to Orion tenants.

[coveralls]

Coverage remained the same at 89.425% when pulling a74ea2b on pooja1pathak:master into 2df1e6c on Orange-OpenSource:master.

[marcc-orange]

Thank you for your contribution @pooja1pathak ! Notify me when you are finished.
Closes #75

[pooja1pathak]

Hi @marcc-orange , I am done with the documentation from my side.
Please guide me further if anything is missing or needs to be added.

[pooja1pathak]

Hi @marcc-orange , I have a query for multi-tenant Cepheus-CEP.
Is Cepheus_CEP is designed to provide multiple subscription for different tenant in multi-tenant mode?

As per my observation every-time CEP receives any configuration, it first unsubscribes from the previous Provider and then subscribe to the new Provider as given in the configuration. In this way Cepheus-CEP have multiple configuration files but only one subscription at a time even when multi-tenancy is enabled.

Is this a bug or I missed something?

[marcc-orange]

This looks like a bug, clearly each tenant has (or shoud have) an instance of a SubscriptionManager, reloading/updating the configuration of a tenant shoud not change subscriptions of other tenants.

[marcc-orange]

It might be easier to just use Docker containers to handle multi-tenancy properly (providing better isolation) than using a shared JVM application if you are not running on a constraint RPi-like platform...

[pooja1pathak]

I tried to use Docker containers for running Cepheus but I am unable to find application.properties or cep.peroperties or any config file which can be used to enable multi-tenancy.

Please guide me with the steps to enable multi-tenancy in Docker container environment.

[pooja1pathak]

Hi @marcc-orange I have added a separate issue for our above discussion #80.

Please review my PR #79 and verify its content for documentation of multi-tenancy in cepheus CEP.