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From "Ben Bromhead (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (CASSANDRA-14361) Allow SimpleSeedProvider to resolve multiple IPs per DNS name
Date Mon, 02 Apr 2018 15:13:00 GMT

     [ https://issues.apache.org/jira/browse/CASSANDRA-14361?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Ben Bromhead updated CASSANDRA-14361:
-------------------------------------
    Description: 
Currently SimpleSeedProvider can accept a comma separated string of IPs or hostnames as the
set of Cassandra seeds. hostnames are resolved via InetAddress.getByName, which will only
return the first IP associated with an A, AAAA or CNAME record.

By changing to InetAddress.getAllByName, existing behavior is preserved, but now Cassandra
can discover multiple IP address per record, allowing seed discovery by DNS to be a little
easier.

Some examples of improved workflows with this change include: 
 * specify the DNS name of a headless service in Kubernetes which will resolve to all IP
addresses of pods within that service. 
 * seed discovery for multi-region clusters via AWS route53, AzureDNS etc
 * Other common DNS service discovery mechanisms.

The only behavior this is likely to impact would be where users are relying on the fact that
getByName only returns a single IP address.

I can't imagine any scenario where that is a sane choice. Even when that choice has been
made, it only impacts the first startup of Cassandra and would not be on any critical path.

> Allow SimpleSeedProvider to resolve multiple IPs per DNS name
> -------------------------------------------------------------
>
>                 Key: CASSANDRA-14361
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-14361
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Configuration
>            Reporter: Ben Bromhead
>            Assignee: Ben Bromhead
>            Priority: Minor
>             Fix For: 4.0
>
>
> Currently SimpleSeedProvider can accept a comma separated string of IPs or hostnames
as the set of Cassandra seeds. hostnames are resolved via InetAddress.getByName, which will
only return the first IP associated with an A, AAAA or CNAME record.
> By changing to InetAddress.getAllByName, existing behavior is preserved, but now Cassandra
can discover multiple IP address per record, allowing seed discovery by DNS to be a little
easier.
> Some examples of improved workflows with this change include: 
>  * specify the DNS name of a headless service in Kubernetes which will resolve to all
IP addresses of pods within that service. 
>  * seed discovery for multi-region clusters via AWS route53, AzureDNS etc
>  * Other common DNS service discovery mechanisms.
> The only behavior this is likely to impact would be where users are relying on the fact
that getByName only returns a single IP address.
> I can't imagine any scenario where that is a sane choice. Even when that choice has
been made, it only impacts the first startup of Cassandra and would not be on any critical
path.



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