Access to the database for 2 Apps

[tim....@googlemail.com]

Hi guys,

how can I get access to one database (cassandra) for 2 different apps, which runs on Appscale.
E.g. one app is store data to the database and the other is only read the stored data.
Is it possible?

Thanks,
Tim

[Navraj Chohan]

Hi Tim,
There is no way to do this straight up but you can modify the code to do such access controls. You would have to modify AppDB/data store_server.py to enable this. Glad to give further instruction if you want to go down this path.

Thanks
Raj

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[tim....@googlemail.com]

Hi Raj,

yes, I want to try it. But first, is it a lot of work to modify the datastore_server.py?
What are the main steps for the modification in datastore_server.py?

Thanks,
Tim

Am Donnerstag, 16. Oktober 2014 20:44:59 UTC+2 schrieb Raj:

Hi Tim,
There is no way to do this straight up but you can modify the code to do such access controls. You would have to modify AppDB/data store_server.py to enable this. Glad to give further instruction if you want to go down this path.

Thanks
Raj

On Oct 16, 2014 11:39 AM, <tim....@googlemail.com> wrote:

Hi guys,

how can I get access to one database (cassandra) for 2 different apps, which runs on Appscale.
E.g. one app is store data to the database and the other is only read the stored data.
Is it possible?

Thanks,
Tim

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[Navraj Chohan]

Hi Tim,

There are a few places where you would need to put in code:

Puts: https://github.com/AppScale/appscale/blob/master/AppDB/datastore_server.py#L3889

Gets: https://github.com/AppScale/appscale/blob/master/AppDB/datastore_server.py#L3929

Deletes: https://github.com/AppScale/appscale/blob/master/AppDB/datastore_server.py#L3973

Queries: https://github.com/AppScale/appscale/blob/master/AppDB/datastore_server.py#L3403

There may be some other places as well. See the different types of request that come in:

https://github.com/AppScale/appscale/blob/master/AppDB/datastore_server.py#L3562

When the request come in they will have certain application IDs. You'll have to add code that does something like this for puts and deletes:

if app_id == "reader_app_id":

 app_id = "writer_app_id"

So now the reader ID will switch to the writer ID, allowing it to access its data.

For the queries you'll have to do query.set_app("writer_app_id").

And add code that just returns empty results or throws a READ_ONLY exceptions if the ID is the writer for read operations (gets and queries).

This wont give you access to composite queries. So if you have things specified in your index.yaml file, it'll require some hacking on the application server side.

Let me know if you need additional clarification.

Thanks,

Raj

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Navraj Chohan (Raj), PhD
Co-Founder of AppScale Systems
A Google Cloud Partner,

Gartner 2014 Cool Vendor, 
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