MySQL Bugs: #43537: MEM agents not resolving hostname-to-IP on each connection

Bug #43537	MEM agents not resolving hostname-to-IP on each connection
Submitted:	10 Mar 2009 17:01	Modified:	20 Apr 2010 15:01
Reporter:	Shawn Green	Email Updates:
Status:	Closed	Impact on me:	None
Category:	MySQL Enterprise Monitor: Agent	Severity:	S3 (Non-critical)
Version:	2.0	OS:	Any (N/A)
Assigned to:	Michael Schuster	CPU Architecture:	Any
Tags:	windmill

Description:
If the IP address of the MEM server changes (for example, due to a vlan switch) the reporting agents are unable to follow. 

How to repeat:
1) Configure MEM server and at least one reporting agent. 

2) Remap the hostname of the MEM server to a new address. 

3) Observe the errors on the agents. 

4) Restart the agent to refresh the IP address of the MEM server. 

5) Observe return to normal operations.

Suggested fix:
Modify the Agent code to avoid any cached hostname resolutions.

the agent doesn't resolve the URL to MEM itself, the entire URL is passed to libcurl which does the necessary steps.
glancing at the libcurl docs i can't see a way to force re-resolving it.
i'm curious: what's the TTL of their MEM DNS record? might they be seeing their own TTL setting here (and restarting MEM simply takes longer than the TTL)?

We would need feedback for the question in the above comment to determine the source of the problem.
Thanks

Diego Medina writes: 
Verified fixed on 2.2.0.1652

Added a note to 2.2.0 changelog: 

        The IP address of the URL used to communicate with                                                                                                
        &merlin_server; would be resolved only during initial startup                                                                                     
        by an individual &merlin_agent;. This causes problems where                                                                                       
        the &merlin_server; is on a virtual IP address and the DNS is                                                                                     
        used to provide failure to a new IP address. IP address                                                                                           
        caching has now been disabled, which should cause the IP                                                                                          
        address to be re-looked up and updated during a failover of                                                                                       
        the &merlin_server;.