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Posted to user@cassandra.apache.org by Pushpendra Rajpoot <pu...@gmail.com> on 2020/08/06 08:47:27 UTC
Connect java application to Cassandra in Kubernetes
We have created a statefulset & headless service to deploy Cassandra in
Kubernetes. Our client is also in the same Kubernetes cluster. We have
identified two ways by which we can find contact point for driver in client
application:
1. Use 'cassandra-headless-service-name' as contactPoints
2. Fetch the IPs of pods from headless-service & externalize the IPs.
Read these IP as contact points when initializing the connection.
So far so good. Above will work if one/some pods are restarted and their IP
changes. In this case, the driver will update the new IP automatically.
*How will this work in case of complete outage (all Cassandra pods down) ?
If all the pods are down and they come back online with different IPs (IP
can change in Kubernetes), how will the application connect to Cassandra?*
*What is the best way to connect Cassandra cluster in Kubernetes with a
client running in the same cluster.*
Regards,
Pushpendra
Re: Connect java application to Cassandra in Kubernetes
Posted by Pushpendra Rajpoot <pu...@gmail.com>.
Thank you John for mentioning the liveness probe. This is something I
didn't think about.
Regards,
Pushpendra
On Fri, Aug 7, 2020 at 8:50 AM John Sanda <jo...@gmail.com> wrote:
> It is worth mentioning that depending on how you configure your client
> application deployment, you should not have to worry about bouncing the
> driver. If you add a liveness probe for your client deployment that relies
> on the driver being able to connect to the cluster, then kubernetes will
> restart the client container when the liveness probe fails. And if you
> configure the driver to connect via the headless service, you will get the
> update endpoints.
>
> On Thu, Aug 6, 2020 at 11:00 PM John Sanda <jo...@gmail.com> wrote:
>
>> Hi Pushpendra
>>
>> You should use the headless service, e.g.,
>>
>> // Note that this code snippet is using v3.x of the driver.
>> // Assume the service is deployed in namespace dev and is
>> // named cassandra-service. The FQDN of the service would then
>> // be cassandra-service.dev.svc.cluster.local. If your client
>> // is deployed in the same namespace, you can reach it with by
>> // cassandra-service without the rest.
>>
>> cluster = Cluster.builder
>> .addContactPoint(headlessService)
>> .build();
>> Session session = cluster.connect();
>>
>> A headless service will resolve to multiple endpoints. The exact
>> endpoints to which it maps will be determined by the label selector you use
>> for your service. You can check this with:
>>
>> $ kubectl get endpoints
>>
>> The service will update the endpoints with any IP address changes. The
>> addContactPoint method calls the following:
>>
>> addContactPoints(*IntetAddress.getAllByName*(headlessService));
>>
>> getAllByName will return all of the endpoints. If the entire C* cluster
>> goes down, you will need to bounce the driver.
>>
>> Cheers
>>
>> John
>>
>> On Thu, Aug 6, 2020 at 4:47 AM Pushpendra Rajpoot <
>> pushpendra.nh.rajpoot@gmail.com> wrote:
>>
>>>
>>> We have created a statefulset & headless service to deploy Cassandra in
>>> Kubernetes. Our client is also in the same Kubernetes cluster. We have
>>> identified two ways by which we can find contact point for driver in client
>>> application:
>>>
>>> 1. Use 'cassandra-headless-service-name' as contactPoints
>>> 2. Fetch the IPs of pods from headless-service & externalize the
>>> IPs. Read these IP as contact points when initializing the connection.
>>>
>>>
>>> So far so good. Above will work if one/some pods are restarted and their
>>> IP changes. In this case, the driver will update the new IP automatically.
>>>
>>> *How will this work in case of complete outage (all Cassandra pods down)
>>> ? If all the pods are down and they come back online with different IPs (IP
>>> can change in Kubernetes), how will the application connect to Cassandra?*
>>>
>>> *What is the best way to connect Cassandra cluster in Kubernetes with a
>>> client running in the same cluster.*
>>>
>>>
>>> Regards,
>>>
>>> Pushpendra
>>>
>>>
>>
>> --
>>
>> - John
>>
>
>
> --
>
> - John
>
Re: Connect java application to Cassandra in Kubernetes
Posted by John Sanda <jo...@gmail.com>.
It is worth mentioning that depending on how you configure your client
application deployment, you should not have to worry about bouncing the
driver. If you add a liveness probe for your client deployment that relies
on the driver being able to connect to the cluster, then kubernetes will
restart the client container when the liveness probe fails. And if you
configure the driver to connect via the headless service, you will get the
update endpoints.
On Thu, Aug 6, 2020 at 11:00 PM John Sanda <jo...@gmail.com> wrote:
> Hi Pushpendra
>
> You should use the headless service, e.g.,
>
> // Note that this code snippet is using v3.x of the driver.
> // Assume the service is deployed in namespace dev and is
> // named cassandra-service. The FQDN of the service would then
> // be cassandra-service.dev.svc.cluster.local. If your client
> // is deployed in the same namespace, you can reach it with by
> // cassandra-service without the rest.
>
> cluster = Cluster.builder
> .addContactPoint(headlessService)
> .build();
> Session session = cluster.connect();
>
> A headless service will resolve to multiple endpoints. The exact endpoints
> to which it maps will be determined by the label selector you use for your
> service. You can check this with:
>
> $ kubectl get endpoints
>
> The service will update the endpoints with any IP address changes. The
> addContactPoint method calls the following:
>
> addContactPoints(*IntetAddress.getAllByName*(headlessService));
>
> getAllByName will return all of the endpoints. If the entire C* cluster
> goes down, you will need to bounce the driver.
>
> Cheers
>
> John
>
> On Thu, Aug 6, 2020 at 4:47 AM Pushpendra Rajpoot <
> pushpendra.nh.rajpoot@gmail.com> wrote:
>
>>
>> We have created a statefulset & headless service to deploy Cassandra in
>> Kubernetes. Our client is also in the same Kubernetes cluster. We have
>> identified two ways by which we can find contact point for driver in client
>> application:
>>
>> 1. Use 'cassandra-headless-service-name' as contactPoints
>> 2. Fetch the IPs of pods from headless-service & externalize the
>> IPs. Read these IP as contact points when initializing the connection.
>>
>>
>> So far so good. Above will work if one/some pods are restarted and their
>> IP changes. In this case, the driver will update the new IP automatically.
>>
>> *How will this work in case of complete outage (all Cassandra pods down)
>> ? If all the pods are down and they come back online with different IPs (IP
>> can change in Kubernetes), how will the application connect to Cassandra?*
>>
>> *What is the best way to connect Cassandra cluster in Kubernetes with a
>> client running in the same cluster.*
>>
>>
>> Regards,
>>
>> Pushpendra
>>
>>
>
> --
>
> - John
>
--
- John
Re: Connect java application to Cassandra in Kubernetes
Posted by John Sanda <jo...@gmail.com>.
Hi Pushpendra
You should use the headless service, e.g.,
// Note that this code snippet is using v3.x of the driver.
// Assume the service is deployed in namespace dev and is
// named cassandra-service. The FQDN of the service would then
// be cassandra-service.dev.svc.cluster.local. If your client
// is deployed in the same namespace, you can reach it with by
// cassandra-service without the rest.
cluster = Cluster.builder
.addContactPoint(headlessService)
.build();
Session session = cluster.connect();
A headless service will resolve to multiple endpoints. The exact endpoints
to which it maps will be determined by the label selector you use for your
service. You can check this with:
$ kubectl get endpoints
The service will update the endpoints with any IP address changes. The
addContactPoint method calls the following:
addContactPoints(*IntetAddress.getAllByName*(headlessService));
getAllByName will return all of the endpoints. If the entire C* cluster
goes down, you will need to bounce the driver.
Cheers
John
On Thu, Aug 6, 2020 at 4:47 AM Pushpendra Rajpoot <
pushpendra.nh.rajpoot@gmail.com> wrote:
>
> We have created a statefulset & headless service to deploy Cassandra in
> Kubernetes. Our client is also in the same Kubernetes cluster. We have
> identified two ways by which we can find contact point for driver in client
> application:
>
> 1. Use 'cassandra-headless-service-name' as contactPoints
> 2. Fetch the IPs of pods from headless-service & externalize the IPs.
> Read these IP as contact points when initializing the connection.
>
>
> So far so good. Above will work if one/some pods are restarted and their
> IP changes. In this case, the driver will update the new IP automatically.
>
> *How will this work in case of complete outage (all Cassandra pods down) ?
> If all the pods are down and they come back online with different IPs (IP
> can change in Kubernetes), how will the application connect to Cassandra?*
>
> *What is the best way to connect Cassandra cluster in Kubernetes with a
> client running in the same cluster.*
>
>
> Regards,
>
> Pushpendra
>
>
--
- John