Improve error reporting in XenD

In the XenD code which deals with dispatching of requests (SrvBase.py) the dispatch process is obviously wrapped in a try/except block. Unfortunately in the except block, the HTTP error code is never updated to indicate a failure condition.

So, for example, if you try to create a domain requesting 3 GB of memory, and Dom0 fails to balloon, XenD will happily still return 'HTTP 202 OK' even though the domain creation failed. This leaves apps talking to XenD no way to discover that there was a failure in the create operation, other than telling the user to look in /var/log/xend.log where the details are logged.

The attached patch sets the HTTP return code to '500 Internal Error' when a request throws an exception. This lets client detect & report the failure of domain creation immediately, improving the end user experiance

As an example user interaction with current behaviour. libvirt is told by XenD that domain creation succeeded, so it goes onto to wait for devices where upon its told there is no such domain:

Starting install...
libvir: Xen Daemon error : POST operation failed: No such domain demo12 Failed to get devices for domain demo12

With the attached patch applied, the initial domain creation failure can be detected & reported immediately:

Starting install...
libvir: Xen Daemon error : POST operation failed: (xend.err 'Error creating domain: The privileged domain did not balloon!') Failed to create domain demo12

Signed-off by: Daniel P. Berrange <[email protected]>

Regards,
Dan.

Signature · 6 lines

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diff -r 68a1b61ecd28 tools/python/xen/web/SrvBase.py

tools/python/xen/web/SrvBase.py +1 -0

@@ -84,6 +84,7 @@ class SrvBase(resource.Resource):
             try:
                 return op_method(op, req)
             except Exception, exn:
+                req.setResponseCode(http.INTERNAL_SERVER_ERROR, "Request failed: " + op)
                 log.exception("Request %s failed.", op)
                 if req.useSxp():
                     return ['xend.err', str(exn)]

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I've not seen this patch appear in xen-unstable. Any chance that it can make it into Xen 3.0.3 release. Its a really triival 1-liner which significantly improves error handling when talking to XenD.

Regards,
Dan.

Quoted 59 lines · Daniel P. Berrange

In the XenD code which deals with dispatching of requests (SrvBase.py) the dispatch process is obviously wrapped in a try/except block. Unfortunately in the except block, the HTTP error code is never updated to indicate a failure condition.

So, for example, if you try to create a domain requesting 3 GB of memory, and Dom0 fails to balloon, XenD will happily still return 'HTTP 202 OK' even though the domain creation failed. This leaves apps talking to XenD no way to discover that there was a failure in the create operation, other than telling the user to look in /var/log/xend.log where the details are logged.

The attached patch sets the HTTP return code to '500 Internal Error' when a request throws an exception. This lets client detect & report the failure of domain creation immediately, improving the end user experiance

As an example user interaction with current behaviour. libvirt is told by XenD that domain creation succeeded, so it goes onto to wait for devices where upon its told there is no such domain:

Starting install...
libvir: Xen Daemon error : POST operation failed: No such domain demo12 Failed to get devices for domain demo12

With the attached patch applied, the initial domain creation failure can be detected & reported immediately:

Starting install...
libvir: Xen Daemon error : POST operation failed: (xend.err 'Error creating domain: The privileged domain did not balloon!') Failed to create domain demo12

Signed-off by: Daniel P. Berrange <[email protected]>

Regards,
Dan.

Signature · 6 lines

|=- Red Hat, Engineering, Emerging Technologies, Boston.  +1 978 392 2496 -=|
|=-           Perl modules: http://search.cpan.org/~danberr/              -=|
|=-               Projects: http://freshmeat.net/~danielpb/               -=|
|=-  GnuPG: 7D3B9505   F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505  -=| 

diff -r 68a1b61ecd28 tools/python/xen/web/SrvBase.py

tools/python/xen/web/SrvBase.py +1 -0

@@ -84,6 +84,7 @@ class SrvBase(resource.Resource):
             try:
                 return op_method(op, req)
             except Exception, exn:
+                req.setResponseCode(http.INTERNAL_SERVER_ERROR, "Request failed: " + op)
                 log.exception("Request %s failed.", op)
                 if req.useSxp():
                     return ['xend.err', str(exn)]

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