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Re: Weird "No Instance Available" and its fix
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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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References: 
 >Weird "No Instance Available" and its fix (From: Mike Schrag <email@hidden>)
 >Re: Weird "No Instance Available" and its fix (From: Ken Anderson <email@hidden>)
 >Re: Weird "No Instance Available" and its fix (From: Mike Schrag <email@hidden>)

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