270 dns log

[ricellis]

What

Added log warnings for long JVM DNS cache TTLs.

How

Added warning level log messages if the TTL is too high or can't be checked.

• If permission is denied to read the configuration property log a warning.
• If the property can be read and parsed, but is longer than 30 s log a warning.
• If the value is the default setting and a SecurityManager is active then log a warning because the TTL is infinite if unconfigured with a SecurityManager.

Testing

Added tests to validate log output:
dnsNoWarningLessThan30
dnsNoWarning0
dnsWarningForever
dnsNoWarning30
dnsWarning31
dnsWarningPermissionDenied
dnsWarningDefaultWithSecurityManager

Issues

Fixes #270

[rhyshort]

I can't see a change that requires this to be imported.

[ricellis]

I changed IDEs and import cleanup must now be turned off :(

[ricellis]

Fixed in ff73d2e

[rhyshort]

+1

[ricellis]

@willholley are you happy with the log messages:

WARNING: DNS cache lifetime may be too long. DNS cache lifetimes in excess of 30 seconds may impede client operation during cluster failover.

and

WARNING: Permission denied to check Java DNS cache TTL. If the cache lifetime is too long cluster failover will be impeded.

?

[willholley]

@ricellis the error messages look fine. Ideally we shouldn't need to prescribe a value (though 30 seconds is probably a good one) and the client should respect the DNS TTL that we return (e.g. see http://mxtoolbox.com/SuperTool.aspx?action=a%3awillholley.cloudant.com&run=toolpage). From what I can tell, this varies between DNS entries - sometimes it's 30 seconds and sometimes up to 5 minutes.

[ricellis]

Thanks, this is logging only as we can't change the behaviour of the JVM - so 30 s is the barrier chosen for the message.