supervising an apache RewriteMap program?

supervising an apache RewriteMap program?

[Robin Bowes]

Hi,

I'm using perl script as an Apache RewriteMap program [1]

Basically, this is started when apache starts and communication is via 
stdin and stdout. A simple program (the example from the link below) is:

#!/usr/bin/perl
$| = 1;
while (<STDIN>) {
     # ...put here any transformations or lookups...
     print $_;
}

I'm using a much more complex example that does DB lookups, etc.

The problem arises when the program exits or dies for some reason - 
apache doesn't restart it.

I'm wondering, could I use supervise or runsv to make sure the rewrite 
map program is restarted?

First issue - the rewritemap program can't take parameters, i.e. it has 
to be specified as a single word. So, I guess I could use a script that 
execs runsv, e.g.:

RewriteMap aypFilterMap    prg:/usr/bin/rewritemap_wrapper.sh

rewritemap_wrapper.sh:
====================================================
#!/bin/bash
exec runsv /var/apache/rewritemap
====================================================

/var/apache/rewritemap/run:
====================================================
#!/bin/bash
exec /usr/bin/myrewritemap.pl
====================================================

Second issue - as I mentioned earlier, apache communicates with the 
rewrite map program through its stdin and stdout. It writes to the 
program's stdin and reads from its stdout.

In normal use, the connected processes are simply:

apache<->myrewritemap.pl

In the configuration above, it's more complex:

apache<->rewritemap_wrapper.sh<->runsv<->run<->myrewritemap.pl

Using the configuration above, would the apache process be connected to 
the stdin and stdout of the myrewritemap.pl script?

What about if/when the myrewritemap.pl script exits and is restarted?

Thanks for any insight into this.

Cheers,

R.

[1] http://httpd.apache.org/docs/2.2/mod/mod_rewrite.html#rewritemap

Re: supervising an apache RewriteMap program?

[Charlie Brady]

On Wed, 9 May 2007, Robin Bowes wrote:

> The problem arises when the program exits or dies for some reason - apache 
> doesn't restart it.

Perhaps this is best addressed as a bug/misfeature in apache.

Re: supervising an apache RewriteMap program?

[Robin Bowes]

Charlie Brady wrote:
>
> On Wed, 9 May 2007, Robin Bowes wrote:
>
>> The problem arises when the program exits or dies for some reason -
>> apache doesn't restart it.
>
> Perhaps this is best addressed as a bug/misfeature in apache.

I can certainly raise a bug against apache for this. However, I'm trying
to use existing tools to come up with a robust solution.

Anyone got any thoughts on how best to achieve this?

R.

Re: supervising an apache RewriteMap program?

[Scott Gifford]

Robin Bowes <robin-lists@robinbowes.com> writes:

> I'm using perl script as an Apache RewriteMap program [1]

[...]

> I'm wondering, could I use supervise or runsv to make sure the rewrite
> map program is restarted?

Perhaps, but the handy things supervise does (like redirect file
descriptors) would be more of a hindrance than a help here, so it
would probably be much easier to wrap your script in another Perl
script that did something like:

  while(1) {
    system("/path/to/real/program");
  }

That's still not perfect; a better solution would patch Apache to
restart the program (as Charlie suggests), or else to send requests
over a socket, which could be listened to by a supervised daemon.

Good luck!

----Scott.