Re: Weird "No Instance Available" and its fix
Re: Weird "No Instance Available" and its fix
- Subject: Re: Weird "No Instance Available" and its fix
- From: Patrick Middleton <email@hidden>
- Date: Thu, 20 Apr 2006 16:30:47 +0100
The computer on which an application is running needs to be
identified in the communications between wotaskd and the application
instances it manages because of configurations with multiple hosts.
In the simplest configuration, Apache and JavaMonitor and wotaskd and
all your applications will be running on a single computer called
localhost; this works.
If your application server host (or hosts) can resolve itself (or
themselves), then applications are liable to advertise their
existence to the local wotaskd using a fully-qualified domain name.
You can add hosts by name or address in JavaMonitor; the
configuration recorded will use fully-qualified domain names.
If a computer changes its hostname (because at boot time, reverse
DNS returned something different) then wotaskd will read its config
file and see information about a computer which is not listed in the
part of the file that names known application server hosts; so it
ignores it, and so wotaskd never starts your applications.
If you are skilled with /bin/hostname and know how to reset or flush
DNS on the application server, you can set the hostname back to what
you think it should be, restart WebObjects, let wotaskd catch up, and
then have all your apps show up -- without needing to reboot. If you
keep tinkering once they're running, you can even have them all show
up as development instances on another computer.
On 20 Apr 2006, at 15:33, Mike Schrag wrote:
Unfortunately this particular case wasn't solved by restarting ...
I did a few desperate restarts of each individual piece during my
flailing :) In this case DNS was just actually wrong and something
in the chain of wotaskd/apache/woadaptor/mod_WebObjects/etc
depended on it not being wrong.
ms
On Apr 20, 2006, at 10:28 AM, Ken Anderson wrote:
Mike,
When I do development on my laptop (with WOHost = localhost) and
plug into someone else's network after sleeping, I find that:
/System/Library/StartupItems/WebObjects/WebObjects restart
works every time. That might help in your circumstance as well.
Ken
On Apr 20, 2006, at 10:12 AM, Mike Schrag wrote:
Occasionally I run into something really odd, and I thought I'd
pass along the solution in case someone else runs into it ...
One of our clients is running a prototype WO app and launching it
from Eclipse. Yesterday they changed the IP of that machine and
all of a sudden, the app just gives everyone's favorite friend
"No instance available". No error messages anywhere. Console
looks fine. After dorking around for quite a while, Brendan
Duddridge recommended I try changing my adaptor URL from
127.0.0.1 to localhost to see if it made any difference. Upon
changing it, instead of no instance available, Safari tells me it
can't find host228.theirdomain.com, which was SUPPOSED to be the
DNS name of the box running the WO app (i.e. it doesn't know
itself by its own name). It turns out that there was ONLY a
reverse DNS entry and not a forward DNS entry. Somewhere deep in
the bowels of WO, this caused a series of explosions that
resulted in silent failure -- my favorite kind of time-wasting
failure. By temporarily adding an /etc/hosts entry, it
immediately started working again.
So the moral of the story is to make sure the name that WO/Apache/
etc are using are resolvable, or you are going to have really
strange problems. At least with Wonder installed (this might
display on regular WO apps also? been a while), it will print
out at startup the InetAddress it's binding to. The toString of
InetAddress is ("x.y.z.w/host.domain.com"). Whatever name is
displayed on the right side of the toString needs to be the name
that is resolved. If you just run locally, it's probably a
rendezvous .local name, which should be fine. But if it's a full-
blown DNS name, make sure that the entry for that name is
configured properly.
Hope this saves someone at least a little time someday ...
ms
-- Patrick
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