Re: [Wrapper-user] Best way to handle dependent processes on Linux/Unix?

[Chuck S. <ch...@co...>]

On Sun, 2003-08-10 at 00:32, Leif Mortenson wrote:
> Chuck,
> This is actually a problem that I have been trying to figure out the
> best way of
> resolving. For system startup, and shutdown. You would do this by
> registering
> tomcat run levels to use a startup order that is lower than apache and a
> shutdown
> order that is lower than apache. I have docs on this for the Debian
> Linux platform.
> I need help from users to get similar pages setup for other Unix/Linux
> platforms.

Leif, I do this on Redhat as well so system startup and shutdown are not
really an issue for me. I am more concerned with restarts (manual or in
response to a JVM hang). I can handle this in a WrapperListener. I asked
in case I missed an easier or better way to do this.

> 
> ... snip ...
> 
> Another problem is that on Windows, if you set up a dependency in the Apache
> service on Tomcat, then stopping Tomcat would also stop the Apache service
> automatically. Then starting the Apache service, would cause the Tomcat
> service
> to be started automatically. I am not currently aware of any such mechanism
> in Linux. That doesn't mean it doesn't exist. As much as I know about
> Linux, I
> have come to the conclusion that I will always be learning more :-)
> 

I believe init is similar to what windows does, but at a lower level.
You could probably mimic Windows' service behavior using a wrapper
script or a custom /etc/initscript.

However you generally use either /etc/rc or init to manage a process,
but not both since init executes /etc/rc on bootup and shutdown. Using
both rc.d scripts and an inittab respawn entry to control a process
could be tricky to do correctly. This may be an avenue to explore. See
the init/telinit, initscript and inittab man pages for more.


> Do you see any other issues that I need to keep in mind? The Jk2 connector
> runs as part of the Apache process doesn't it? Or is that yet another
> process?

The JK2 connector runs in the Apache process, but uses a named pipe to
communicate with Tomcat. The named pipe can be deleted by a careless
user or can hang due to errors in the OS which is why I need an
end-to-end check from Apache -> Tomcat -> Apache. I can call wget on a
URL to do this and call JSW restart, but I was curious if there is an
API hook or a communication interface into the native wrapper.

For example I use fifo files to communicate and control some of my
applications. The application has a listener that blocks on the fifo
read until it receives something and then creates a new thread to handle
the action associated with the fifo input. You could also use sockets to
do the same thing, but when both processes are on the same machine a
fifo has some advantages such as the ability to queue up events while
the target application is down.

I appreciate the response and look forward to using JSW to get a better
handle on my servers.

Thanks,
Chuck