[CASSANDRA-14361] Allow SimpleSeedProvider to resolve multiple IPs per DNS name

• Type: Improvement
• Status: Resolved
• Priority: Low
• Resolution: Fixed
• Fix Version/s: 5.0-alpha1, 5.0
• Component/s: Local/Config
• Complexity: Normal

Source Control Link

https://github.com/apache/cassandra/commit/b07c3127cce7e1a8b9d4c34e1359539e12f1b4a7

Test and Documentation Plan

ci

• Assignee: Stefan Miklosovic
• Reporter: Ben Bromhead

Authors

Stefan Miklosovic

Reviewers

Andres de la Peña

• Created: 02/Apr/18 15:00
• Updated: 12/Sep/23 13:02
• Resolved: 18/Jan/23 09:50

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.

Issue Links

• is blocked by: CASSANDRA-18152 mockito-inline causes tests to fail beacause o.a.c.distributed.mock.nodetool.InternalNodeProbe spies on StorageServiceMBean
• links to: TRUNK PR
• links to: WIP-14361