Re: [Wrapper-user] Newbie (?) Questions

[Leif M. <le...@ta...>]

Georg Schmid wrote:

> a few hours ago I downloaded the Wrapper 3.0.4 in order to improve the 
> uptime of my JBoss servers. Everything works fine so far, but now I am 
> not sure anymore, whether Wrapper can solve my problems.
>
> 1) Restarting after OutOfMemory exceptions works after defining the 
> appropriate filter. I also want the wrapper to restart the server at 
> most 5 times. When I tested this by specifying 8 MB max. heap, the 
> server was restarted continuously (had to kill it after jvm 7 came up). 

The wrapper.max_failed_invocations property only controls the number of 
restarts due to a failed startup.  If the JVM is restarted due to a call 
to WrapperManager.restart() or due to a filter, as in your case, then 
there is no limit to the number of times that the JVM will be 
restarted.   If you think about it, this is good behavior.   If your 
application runs out of memory once per day, you would want it to always 
be restarted.  Not restart for 5 days and then give up and quit.

In this case, the Wrapper is working as expected.  In general, if your 
application is running out of memory, that is a bug in your 
application.  The Wrapper makes it possible to work around such problems 
temporarily, but they really should be fixed at some point.

> 2) The second problem is, that the (locally running, nohup-started) 
> servers go down, when the network goes down. They seem to get a 
> "normal" TERM, just like pressing Ctrl-C or issuing a kill (without 
> -9). JBoss shuts down cleanly, working its shutdown hook, but Wrapper 
> does not restart the process, as I expected. I introduced a filter, 
> that checks for "Shutting down the JVM" string and then triggers a 
> RESTART. The filter matches, but no restart occurs, instead the 
> wrapper stops. 

If your OS is sending a TERM signal to the JVM and Wrapper, then it is 
correct that the Wrapper is quitting.   Catching the message using a 
filter and attempting to restart will not work because the Wrapper is 
already trying to shut itself down.   Processes should always respond to 
a kill TERM by exiting gracefully.

Please explain if I am missing something.  But it seems like the Wrapper 
is behaving correctly here.  If it were to respond to a TERM signal by 
restarting the JVM then there would be no way to kill the Wrapper other 
than a kill -9, which would of course be bad.

> 3) I could not find a parameter to control the ping frequency (not the 
> timeout). The ping slows down the application, and for a server, that 
> should be running for half a year a ping every 30 seconds or similar 
> would be good enough. 

There is already a feature request to be able to control the ping 
time.   But how are you seeing that the ping is slowing down your 
application.   Theoretically that is true as there is additional work 
being done.  But it is very insignificant.  The longer the ping 
interval, the less responsive the Wrapper will be to a hung JVM.  
Pinging once every 5 seconds with debug output off has never caused any 
noticeable performance issues in my experience.

Cheers,
Leif