Hi, all
Openstack APIs interact with each other and external systems partially by
passing of HTTP errors. The only valuable difference between types of
exceptions is HTTP-codes, but current codes are generalized, so external
system can’t distinguish what actually happened.
As an example two different failures below differs only by error message:
request:
POST /v2/790f5693e97a40d38c4d5bfdc45acb09/servers HTTP/1.1
Host: 192.168.122.195:8774
X-Auth-Project-Id: demo
Accept-Encoding: gzip, deflate, compress
Content-Length: 189
Accept: application/json
User-Agent: python-novaclient
X-Auth-Token: 2cfeb9283d784cfba694f3122ef413bf
Content-Type: application/json
{"server": {"name": "demo", "imageRef":
"171c9d7d-3912-4547-b2a5-ea157eb08622", "key_name": "test", "flavorRef":
"42", "max_count": 1, "min_count": 1, "security_groups": [{"name": "bar"}]}}
response:
HTTP/1.1 400 Bad Request
Content-Length: 118
Content-Type: application/json; charset=UTF-8
X-Compute-Request-Id: req-a995e1fc-7ea4-4305-a7ae-c569169936c0
Date: Fri, 23 Jan 2015 10:43:33 GMT
{"badRequest": {"message": "Security group bar not found for project
790f5693e97a40d38c4d5bfdc45acb09.", "code": 400}}
and
request:
POST /v2/790f5693e97a40d38c4d5bfdc45acb09/servers HTTP/1.1
Host: 192.168.122.195:8774
X-Auth-Project-Id: demo
Accept-Encoding: gzip, deflate, compress
Content-Length: 192
Accept: application/json
User-Agent: python-novaclient
X-Auth-Token: 24c0d30ff76c42e0ae160fa93db8cf71
Content-Type: application/json
{"server": {"name": "demo", "imageRef":
"171c9d7d-3912-4547-b2a5-ea157eb08622", "key_name": "foo", "flavorRef":
"42", "max_count": 1, "min_count": 1, "security_groups": [{"name":
"default"}]}}
response:
HTTP/1.1 400 Bad Request
Content-Length: 70
Content-Type: application/json; charset=UTF-8
X-Compute-Request-Id: req-87604089-7071-40a7-a34b-7bc56d0551f5
Date: Fri, 23 Jan 2015 10:39:43 GMT
{"badRequest": {"message": "Invalid key_name provided.", "code": 400}}
The former specifies an incorrect security group name, and the latter an
incorrect keypair name. And the problem is, that just looking at the
response body and HTTP response code an external system can’t understand
what exactly went wrong. And parsing of error messages here is not the way
we’d like to solve this problem.
Another example for solving this problem is AWS EC2 exception codes [1]
So if we have some service based on Openstack projects it would be useful
to have some concrete error codes(textual or numeric), which could allow to
define what actually goes wrong and later correctly process obtained
exception. These codes should be predefined for each exception, have
documented structure and allow to parse exception correctly in each step of
exception handling.
So I’d like to discuss implementing such codes and its usage in openstack
projects.
[1] -
http://docs.aws.amazon.com/AWSEC2/latest/APIReference/errors-overview.html
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