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From "Jon Haddad (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-14361) Allow SimpleSeedProvider to resolve multiple IPs per DNS name
Date Wed, 04 Apr 2018 15:06:00 GMT


Jon Haddad commented on CASSANDRA-14361:

Well, the behavior can be a bit surprising, and possibly could affect gossip convergence.
 The seed gossip round is to accelerate convergence time, although I've never seen it proven
that it works as advertised.  

It might be a good idea to cap the number of seeds we allow gossip to use there.  There has
been talk of a changing the seed round behavior in CASSANDRA-9206, might be worth a read.

Adding [~jasobrown].

> Allow SimpleSeedProvider to resolve multiple IPs per DNS name
> -------------------------------------------------------------
>                 Key: CASSANDRA-14361
>                 URL:
>             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
> 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

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