Using an ELB to front Cassandra Cluster in AWS

[Lahiru]

Hi Users,

I have a scenario where I want to expose my private Cassandra Cluster to external application, so I configured an ELB (secured the ELB only to accessed by my application instance) and attached all my Cassandra nodes as listeners and opened the two the ports 9042, 9160 and forward to the listeners.

I can successfully connect to the ELB and access the data without any issue, but in this thread[1] it tells it might not work as we expects but its not very clear why.

Is there a better way to solve this issue (I am considering the securing Cassandra Cluster as an option too).

[1]https://groups.google.com/a/lists.datastax.com/forum/#!topic/java-driver-user/jtlLuRpw5nY

Regards

Lahiru

[Olivier Michallat]

Hi,

The driver needs a separate IP address for each node that it connects to. If you hide your nodes behind an ELB, the driver will see them as a single host, so that defeats its built-in load balancing and failover logic.

So if you want to connect directly, you need a public IP for each node.

You can declare it as the broadcast_rpc_address in cassandra.yaml,  but that means all applications will have to go through these addresses.

If you only have one "external" application, and other "internal" applications that should use the private addresses, an alternate solution is to use an AddressTranslator in the external app. The Address resolution section in our docs has more information about that.

As an alternative, you could have an extra layer between your external application and your database, such as a REST service.

--

Olivier Michallat

Driver & tools engineer, DataStax

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[Anibal Bicho DBZ Capotorto]

on a slightly different approach to this question.

if I have all my cassandra nodes behind an ELB, but the clients also have the possibility of connecting to the cassandra nodes directly (same subnet, etc), is the ELB a viable option to avoid configuring each cassandra hostname/ip in the clients? 

I was told the initial connection is to figure out which node has the data I'm looking for and then there is a direct connection to that node afterwards , in my scenario, this connection will bypass the elb

Thanks

Bicho

[Anibal Bicho DBZ Capotorto]

btw "no, that is not how it works" is as sufficient answer :D