Faults¶
This doc explains how to understand what has happened to your API request.
Every HTTP request has a status code. 2xx codes signify the API call was a success. However, that is often not the end of the story. That generally only means the request to start the operation has been accepted. It does not mean the action you requested has successfully completed.
Tracking Errors by Request ID¶
There are two types of request ID.
Type |
Description |
|---|---|
Local request ID |
Locally generated unique request ID by each service and different between
all services (Nova, Cinder, Glance, Neutron, etc.) involved
in that operation. The format is |
Global request ID |
User specified request ID which is utilized as common identifier
by all services (Nova, Cinder, Glance, Neutron, etc.) involved
in that operation. This request ID is same among all services involved
in that operation.
The format is |
It is extremely common for clouds to have an ELK (Elastic Search, Logstash, Kibana) infrastructure consuming their logs. The only way to query these flows is if there is a common identifier across all relevant messages. The global request ID immediately makes existing deployed tooling better for managing OpenStack.
Request Header
In each REST API request, you can specify the global request ID
in X-Openstack-Request-Id header, starting from microversion 2.46.
The format must be req- + UUID (UUID4).
If not in accordance with the format, the global request ID is ignored by Nova.
Request header example:
X-Openstack-Request-Id: req-3dccb8c4-08fe-4706-a91d-e843b8fe9ed2
Response Header
In each REST API request, X-Compute-Request-Id is returned
in the response header.
Starting from microversion 2.46, X-Openstack-Request-Id is also returned
in the response header.
X-Compute-Request-Id and X-Openstack-Request-Id are local request IDs.
The global request IDs are not returned.
Response header example:
X-Compute-Request-Id: req-d7bc29d0-7b99-4aeb-a356-89975043ab5e
X-Openstack-Request-Id: req-d7bc29d0-7b99-4aeb-a356-89975043ab5e
Server Actions¶
Most server action APIs are asynchronous. Usually the API service will do
some minimal work and then send the request off to the nova-compute service
to complete the action and the API will return a 202 response to the client.
The client will poll the API until the operation completes, which could be a
status change on the server but is usually at least always waiting for the
server OS-EXT-STS:task_state field to go to null indicating the action
has completed either successfully or with an error.
If a server action fails and the server status changes to ERROR an
instance fault will be shown with the server details.
The os-instance-actions API allows users end users to list the outcome of
server actions, referencing the requested action by request id. This is useful
when an action fails and the server status does not change to ERROR.
To illustrate, consider a server (vm1) created with flavor m1.tiny:
$ openstack server create --flavor m1.tiny --image cirros-0.4.0-x86_64-disk --wait vm1
+-----------------------------+-----------------------------------------------------------------+
| Field | Value |
+-----------------------------+-----------------------------------------------------------------+
| OS-DCF:diskConfig | MANUAL |
| OS-EXT-AZ:availability_zone | nova |
| OS-EXT-STS:power_state | Running |
| OS-EXT-STS:task_state | None |
| OS-EXT-STS:vm_state | active |
| OS-SRV-USG:launched_at | 2019-12-02T19:14:48.000000 |
| OS-SRV-USG:terminated_at | None |
| accessIPv4 | |
| accessIPv6 | |
| addresses | private=10.0.0.60, fda0:e0c4:2764:0:f816:3eff:fe03:806 |
| adminPass | NgascCr3dYo4 |
| config_drive | |
| created | 2019-12-02T19:14:42Z |
| flavor | m1.tiny (1) |
| hostId | 22e88bec09a7e33606348fce0abac0ebbbe091a35e29db1498ec4e14 |
| id | 344174b8-34fd-4017-ae29-b9084dcf3861 |
| image | cirros-0.4.0-x86_64-disk (cce5e6d6-d359-4152-b277-1b4f1871557f) |
| key_name | None |
| name | vm1 |
| progress | 0 |
| project_id | b22597ea961545f3bde1b2ede0bd5b91 |
| properties | |
| security_groups | name='default' |
| status | ACTIVE |
| updated | 2019-12-02T19:14:49Z |
| user_id | 046033fb3f824550999752b6525adbac |
| volumes_attached | |
+-----------------------------+-----------------------------------------------------------------+
The owner of the server then tries to resize the server to flavor m1.small
which fails because there are no hosts available on which to resize the server:
$ openstack server resize --flavor m1.small --wait vm1
Complete
Despite the openstack command saying the operation completed, the server shows
the original m1.tiny flavor and the status is not VERIFY_RESIZE:
$ openstack server show vm1 -f value -c status -c flavor
m1.tiny (1)
ACTIVE
Since the status is not ERROR there are is no fault field in the server
details so we find the details by listing the events for the server:
$ openstack server event list vm1
+------------------------------------------+--------------------------------------+--------+----------------------------+
| Request ID | Server ID | Action | Start Time |
+------------------------------------------+--------------------------------------+--------+----------------------------+
| req-ea1b0dfc-3186-42a9-84ff-c4f4fb130fae | 344174b8-34fd-4017-ae29-b9084dcf3861 | resize | 2019-12-02T19:15:35.000000 |
| req-4cdc4c93-0668-4ae6-98c8-a0a5fcc63d39 | 344174b8-34fd-4017-ae29-b9084dcf3861 | create | 2019-12-02T19:14:42.000000 |
+------------------------------------------+--------------------------------------+--------+----------------------------+
To see details about the resize action, we use the Request ID for that
action:
$ openstack server event show vm1 req-ea1b0dfc-3186-42a9-84ff-c4f4fb130fae
+---------------+------------------------------------------+
| Field | Value |
+---------------+------------------------------------------+
| action | resize |
| instance_uuid | 344174b8-34fd-4017-ae29-b9084dcf3861 |
| message | Error |
| project_id | b22597ea961545f3bde1b2ede0bd5b91 |
| request_id | req-ea1b0dfc-3186-42a9-84ff-c4f4fb130fae |
| start_time | 2019-12-02T19:15:35.000000 |
| user_id | 046033fb3f824550999752b6525adbac |
+---------------+------------------------------------------+
We see the message is “Error” but are not sure what failed. By default the
event details for an action are not shown to users without the admin role so
use microversion 2.51 to see the events (the events field is JSON-formatted
here for readability):
$ openstack --os-compute-api-version 2.51 server event show vm1 req-ea1b0dfc-3186-42a9-84ff-c4f4fb130fae -f json -c events
{
"events": [
{
"event": "cold_migrate",
"start_time": "2019-12-02T19:15:35.000000",
"finish_time": "2019-12-02T19:15:36.000000",
"result": "Error"
},
{
"event": "conductor_migrate_server",
"start_time": "2019-12-02T19:15:35.000000",
"finish_time": "2019-12-02T19:15:36.000000",
"result": "Error"
}
]
}
By default policy configuration a user with the admin role can see a
traceback for each failed event just like with an instance fault:
$ source openrc admin admin
$ openstack --os-compute-api-version 2.51 server event show 344174b8-34fd-4017-ae29-b9084dcf3861 req-ea1b0dfc-3186-42a9-84ff-c4f4fb130fae -f json -c events
{
"events": [
{
"event": "cold_migrate",
"start_time": "2019-12-02T19:15:35.000000",
"finish_time": "2019-12-02T19:15:36.000000",
"result": "Error",
"traceback": " File \"/opt/stack/nova/nova/conductor/manager.py\",
line 301, in migrate_server\n host_list)\n
File \"/opt/stack/nova/nova/conductor/manager.py\", line 367, in
_cold_migrate\n raise exception.NoValidHost(reason=msg)\n"
},
{
"event": "conductor_migrate_server",
"start_time": "2019-12-02T19:15:35.000000",
"finish_time": "2019-12-02T19:15:36.000000",
"result": "Error",
"traceback": " File \"/opt/stack/nova/nova/compute/utils.py\",
line 1410, in decorated_function\n return function(self, context,
*args, **kwargs)\n File \"/opt/stack/nova/nova/conductor/manager.py\",
line 301, in migrate_server\n host_list)\n
File \"/opt/stack/nova/nova/conductor/manager.py\", line 367, in
_cold_migrate\n raise exception.NoValidHost(reason=msg)\n"
}
]
}
Logs¶
All logs on the system, by default, include the global request ID and the local request ID when available. This allows an administrator to track the API request processing as it transitions between all the different nova services or between nova and other component services called by nova during that request.
When nova services receive the local request IDs of other components in the
X-Openstack-Request-Id header, the local request IDs are output to logs
along with the local request IDs of nova services.
Tip
If a session client is used in client library, set DEBUG level to
the keystoneauth log level. If not, set DEBUG level to the client
library package. e.g. glanceclient, cinderclient.
Sample log output is provided below.
In this example, nova is using local request ID
req-034279a7-f2dd-40ff-9c93-75768fda494d,
while neutron is using local request ID
req-39b315da-e1eb-4ab5-a45b-3f2dbdaba787:
Jun 19 09:16:34 devstack-master nova-compute[27857]: DEBUG keystoneauth.session [None req-034279a7-f2dd-40ff-9c93-75768fda494d admin admin] POST call to network for http://10.0.2.15:9696/v2.0/ports used request id req-39b315da-e1eb-4ab5-a45b-3f2dbdaba787 {{(pid=27857) request /usr/local/lib/python2.7/dist-packages/keystoneauth1/session.py:640}}
Note
The local request IDs are useful to make ‘call graphs’.
Instance Faults¶
Nova often adds an instance fault DB entry for an exception that happens
while processing an API request. This often includes more administrator
focused information, such as a stack trace. For a server with status
ERROR or DELETED, a GET /servers/{server_id} request will include
a fault object in the response body for the server resource. For
example:
GET https://10.211.2.122/compute/v2.1/servers/c76a7603-95be-4368-87e9-7b9b89fb1d7e
{
"server": {
"id": "c76a7603-95be-4368-87e9-7b9b89fb1d7e",
"fault": {
"created": "2018-04-10T13:49:40Z",
"message": "No valid host was found.",
"code": 500
},
"status": "ERROR",
...
}
}
Notifications¶
In many cases there are also notifications emitted that describe the error. This is an administrator focused API, that works best when treated as structured logging.
Synchronous Faults¶
If an error occurs while processing our API request, you get a non 2xx API status code. The system also returns additional information about the fault in the body of the response.
Example: Fault: JSON response
{
"itemNotFound":{
"code": 404,
"message":"Aggregate agg_h1 could not be found."
}
}
The error code is returned in the body of the response for convenience.
The message section returns a human-readable message that is appropriate
for display to the end user. The details section is optional and may
contain information–for example, a stack trace–to assist in tracking
down an error. The details section might or might not be appropriate for
display to an end user.
The root element of the fault (such as, computeFault) might change depending on the type of error. The following link contains a list of possible elements along with their associated error codes.
For more information on possible error code, please see: http://specs.openstack.org/openstack/api-wg/guidelines/http/response-codes.html
Asynchronous faults¶
An error may occur in the background while a server is being built or while a server is executing an action.
In these cases, the server is usually placed in an ERROR state. For some
operations, like resize, it is possible that the operation fails but
the instance gracefully returned to its original state before attempting the
operation. In both of these cases, you should be able to find out more from
the Server Actions API described above.
When a server is placed into an ERROR state, a fault is embedded in the
offending server. Note that these asynchronous faults follow the same format
as the synchronous ones. The fault contains an error code, a human readable
message, and optional details about the error. Additionally, asynchronous
faults may also contain a created timestamp that specifies when the fault
occurred.
Example: Server in error state: JSON response
{
"server": {
"id": "52415800-8b69-11e0-9b19-734f0000ffff",
"tenant_id": "1234",
"user_id": "5678",
"name": "sample-server",
"created": "2010-08-10T12:00:00Z",
"hostId": "e4d909c290d0fb1ca068ffafff22cbd0",
"status": "ERROR",
"progress": 66,
"image" : {
"id": "52415800-8b69-11e0-9b19-734f6f007777"
},
"flavor" : {
"id": "52415800-8b69-11e0-9b19-734f216543fd"
},
"fault" : {
"code" : 500,
"created": "2010-08-10T11:59:59Z",
"message": "No valid host was found. There are not enough hosts available.",
"details": [snip]
},
"links": [
{
"rel": "self",
"href": "http://servers.api.openstack.org/v2/1234/servers/52415800-8b69-11e0-9b19-734f000004d2"
},
{
"rel": "bookmark",
"href": "http://servers.api.openstack.org/1234/servers/52415800-8b69-11e0-9b19-734f000004d2"
}
]
}
}
