17 KiB
Enhance Placement Process
This specification supports the placement functionality for VNF instance and enhances the applicability of Tacker to various systems.
Problem description
The placement constraints are defined in ETSI NFV-SOL 003 v3.3.1 1 and that VNFM sends to NFVO in order
to the resource placement decision. In VNF Lifecycle Management (LCM),
there are some cases that VNFs are not deployed due to placement
constraints or lack of availability zone's resources. From a
high-availability perspective, Tacker needs to implement a
fallbackBestEffort
option in Grant Request and availability
zone reselection functions.
Proposed change
1. Add fallbackBestEffort parameter
fallbackBestEffort
is to look for an alternate best
effort placement for specified resources cannot be allocated based on
specified placement constraint and defined in ETSI NFV-SOL 003 v3.3.12. On this specification, Tacker will
support additional parameter fallbackBestEffort
in Grant
Request (PlacementConstrains
) and Tacker configuration
settings. We will modify Tacker conductor and tacker.conf
.
Add definitions details are described in 3. Add definitions to the
configuration file<configuration-file>
.
GrantRequest.PlacementConstrains
Attribute name Data type Cardinality Description fallbackBestEffort Boolean 0..1 Indication if the constraint is handled with fall back best effort. Default value is "false".
Note
If fallbackBestEffort
is present in placement
constraints and set to "true", the NFVO shall process the
Affinity/Anti-Affinity constraint in a best effort manner, in which
case, if specified resources cannot be allocated based on specified
placement constraint, the NFVO looks for an alternate best effort
placement for the specified resources to be granted.
2. Availability zone reselection
The VNFLCM v2 API (instantiate/heal/scale for VNF) process can change the availability zone to be used from the one notified by the NFVO if necessary. If the availability zone notified by the NFVO has insufficient resources, the VNF is created/updated in a different availability zone. The availability zone is reselected considering Affinity/Anti-Affinity and re-create/update until there are no more candidates.
1) Flowchart of availability zone reselection
- blockdiag {
-
orientation = portrait; edge_layout = flowchart;
create [shape=flowchart.condition,label='stack create/update']; start [shape=beginpoint]; lin [shape=flowchart.loopin,label='stack create/updatenin other AZ']; recreate [shape=flowchart.condition,label='stack create/update']; lout [shape=flowchart.loopout,label='no more AZncandidates']; failure [shape=endpoint,label='end']; success [shape=endpoint,label='end'];
class none [shape=none]; n [class=none];
start -> create [label='NFVO AZ'] create -> lin [label=error] lin -> recreate [label='other AZ'] recreate -> lout [label='error'] lout -> failure [label='failure'];
create -> success;
recreate -> n [dir=none] n -> success [label='success'];
}
The procedure consists of the following steps as illustrated in above flow:
- Execute "stack create/update" in the availability zone notified by the NFVO.
- If an error occurs in 1, get the availability zone list.
Availability zone list details are described in
2) Get and manage availability zone list<az-list>
. - Select an availability zone (excluding the Availability Zone where
the error occurred) randomly in compliance with Affinity/Anti-Affinity
from the availability zone list obtained in 2, and re-execute “stack
create/update”. Reselection policy details are described in
3) Availability zone reselection policy<reselection-policy>
. - If "stack create/update" in the availability zone reselected in 3
becomes an error, reselect the availability zone and repeat until "stack
create/update" succeeds or until all availability zone candidates fail.
Detecting error details are described in
4) Detection method of insufficient resource error<detection-method>
.
2) Get and manage availability zone list
Get availability zone list
Extract all availability zones as candidates for reselection without limiting the availability zones to be reselected. Although it is possible to extract only availability zones permitted by Grant as candidates for reselection, this is not adopted in this Spec because it depends on the NFVO product specifications.
The concept of availability zone exists for Compute/Volume/Network, but this Spec targets only Compute. The reason is that SOL(SOL003 v3.3.1 Type: GrantInfo 3) specifies that the zoneId of GrantInfo, which is the data type of addResources, etc., is usually specified as a COMPUTE resource.
Note
SOL003 v3.3.1 Type: GrantInfo
Reference to the identifier of the "ZoneInfo" structure in the "Grant" structure defining the resource zone into which this resource is to be placed. Shall be present for new resources if the zones concept is applicable to them (typically, Compute resources) and shall be absent for resources that have already been allocated. Shall be present for new resources if the zones concept is applicable to them (typically, Compute resources) and shall be absent for resources that have been allocated.
Call the Compute-API "GetDetailedAvailabilityZoneInformation" 4 to get the availability zones from the "hosts" response associated with "nova-compute".
Compute endpoints are obtained in the following way.
Manage availability zone list
Keep in on-memory until availability zone reselection iterations are completed, and discard after completion (no storage in DB).
Note
Error-Handling Retry consideration
Since the availability zone list is not saved and is retrieved again, there is no guarantee that the availability zone is reselected in the same order when Retry is executed.
3) Availability zone reselection policy
Availability zones in error are excluded from the reselection candidates, and Availability zones are reselected randomly in compliance with Affinity/Anti-Affinity of PlacementConstraint.
The availability zone in error can be identified in the following way.
- Call Heat-API "Show stack details" after an error occurs in "stack create/update"
- Identify the VDU where the error occurred due to insufficient resource by the stack_status_reason in the response of 1.
- Identify the availability zone by the VDU identified in 2.
Note
Insufficient resource in availability zones that once failed during reselection attempts may be resolved, but the availability zones will not be reselected. In Scale/Heal operations, VDUs that have already been deployed will not be re-created.
Availability zone reselection for each PlacementConstraint is as follows.
Precondition: availability zone AZ-1/AZ-2/AZ-3 exist and VNF VDU-1/VDU-2 are deployed
PlacementConstraint is Anti-Affinity
- Before reselection, the following attempts to deploy failed (AZ-1
has insufficient resource)
- VDU-1: AZ-1
- VDU-2: AZ-2
- Reselect the following (except AZ-1, select AZ-2/AZ-3 in compliance
with Anti-Affinity)
- VDU-1: AZ-2
- VDU-2: AZ-3
Note
The above is an example, and it is possible that the reverse availability zones are selected for VDU-1 and VDU-2, but it is guaranteed that they will not be the same availability zone.
- Before reselection, the following attempts to deploy failed (AZ-1
has insufficient resource)
PlacementConstraint is Affinity
- Before reselection, attempt to deploy in the following and fail
(AZ-1 has insufficient resource)
- VDU-1: AZ-1
- VDU-2: AZ-1
- Reselect the following (except AZ-1, select AZ-2/AZ-3 in compliance
with Affinity)
- VDU-1: AZ-2
- VDU-2: AZ-2
Note
The above is an example, and it is possible that the availability zone AZ-3 is selected for VDU-1 and VDU-2, but it is guaranteed that they will be the same availability zone.
- Before reselection, attempt to deploy in the following and fail
(AZ-1 has insufficient resource)
4) Detection method of insufficient resource error
When "stack create/update" fails, it is detected from "Show stack details" 7 of Heat-API response whether the failure is due to insufficient resources. The error message that indicates insufficient resources is extracted from the parameter "stack_status_reason" in the response.
Note
In the case of insufficient resources, the error occurs after "stack create/update" returns an acceptance response, so the "Show stack details" response is used to detect the cause.
The following is an example of an error message stored in "stack_status_reason" when resources are insufficient.
- ex1) Set the flavor defined in “OS::Nova::Server” to a large value
that cannot be deployed (not enough storage/not enough vcpu/not enough
memory).
- Resource CREATE failed: ResourceInError: resources.<VDU-name>: Went to status ERROR due to “Message: No valid host was found. , Code: 500”
- ex2) Specifies an extra-spec that cannot be assigned for the flavor
defined in "OS::Nova::Server."
- Resource CREATE failed: ResourceInError: resources.<VDU-name>: Went to status ERROR due to “Message: Exceeded maximum number of retries. Exhausted all hosts available for retrying build failures for instance <server-UUID>., Code: 500”
Error messages that Tacker detects as insufficient resources are
specified by a regular expression in the configuration file. Add
definitions details are described in 3. Add definitions to the
configuration file<configuration-file>
.
By changing the method of specifying this regular expression in accordance with the operational policy, it is possible to flexibly set a policy to detect more error messages as insufficient resource with a higher tolerance for misdetection, or to detect only specific error messages as insufficient resource.
- ex1) Regular expression for a policy to detect more error messages
as insufficient resource by increasing the tolerance for
misclassification
- Resource CREATE failed:(. *)
- ex2) Regular expression to specify the policy to detect more error
messages as insufficient resource with higher tolerance for false
positives
- Resource CREATE failed: ResourceInError: resources(. *): Went to status ERROR due to "Message: No valid host was found. *): Went to status ERROR due to "Message: Exceeded maximum number of retries. Exhausted all hosts available for retrying build failures for instance(. *). , Code: 500".
5) AutoScalingGroup consideration
In BaseHOT which includes AutoScalingGroup definitions, there is a constraint that each VNFC associated with a VDU under AutoScalingGroup cannot be set to Anti-Affinity for the availability zone. This constraint is due to the constraint in the HOT specification that availability zones can only be set for each VDU under the AutoScalingGroup. This constraint occurs not only at the time of reselection, but also at the time of initial execution. Therefore, BaseHOT which includes AutoScalingGroup definitions, ignores the PlacementConstraint for each VNFC associated with a VDU and reselects a single availability zone for each VDU under the AutoScalingGroup. (Always set to Affinity.)
top HOT:
resources:
VDU1_scale_group:
type: OS::Heat::AutoScalingGroup
properties:
min_size: 1
max_size: 3
desired_capacity: { get_param: [ nfv, VDU, VDU1, desired_capacity ] }
resource:
type: VDU1.yaml
properties:
flavor: { get_param: [ nfv, VDU, VDU1, computeFlavourId ] }
image: { get_param: [ nfv, VDU, VDU1-VirtualStorage, vcImageId ] }
zone: { get_param: [ nfv, VDU, VDU1, locationConstraints] }
net1: { get_param: [ nfv, CP, VDU1_CP1, network] }
net2: { get_param: [ nfv, CP, VDU1_CP2, network ] }
subnet1: { get_param: [nfv, CP, VDU1_CP1, fixed_ips, 0, subnet ]}
subnet2: { get_param: [nfv, CP, VDU1_CP2, fixed_ips, 0, subnet ]}
net3: { get_resource: internalVL1 }
net4: { get_resource: internalVL2 }
net5: { get_resource: internalVL3 }
nested HOT:
resources:
VDU1:
type: OS::Nova::Server
properties:
flavor: { get_param: flavor }
name: VDU1
block_device_mapping_v2: [{"volume_id": { get_resource: VDU1-VirtualStorage }}]
networks:
- port:
get_resource: VDU1_CP1
- port:
get_resource: VDU1_CP2
- port:
get_resource: VDU1_CP3
- port:
get_resource: VDU1_CP4
- port:
get_resource: VDU1_CP5
availability_zone: { get_param: zone }
As shown above, top HOT specifies a single "zone" (availability zone) for each VDU under the AutoScalingGroup, so each VNFC associated with a VDU under the AutoScalingGroup is in the same availability zone.
3. Add definitions to the configuration file
Add the following definition to the tacker.conf
file.
Boolean value of "GrantRequest.PlacementConstrains.fallbackBestEffort"
Default value: "false"
Whether or not to reselect availability zone
Default value: not to reselect
Regular expression for detecting insufficient resource error
Default value: regular expression for insufficient resource error
Note
Consider the regular expression that can catch stack create and stack update errors.
Maximum number of retries for reselection of availability zone
Default value: no upper limit
Note
Consider the case where there are a large number of availability zones and the availability zone reselection process takes too long.
Data model impact
None
REST API impact
None
Security impact
None
Notifications impact
None
Other end user impact
None
Performance Impact
None
Other deployer impact
None
Developer impact
None
Implementation
Assignee(s)
- Primary assignee:
-
Yuta Kazato <yuta.kazato.nw@hco.ntt.co.jp>
Hirofumi Noguchi <hirofumi.noguchi.rs@hco.ntt.co.jp>
- Other contributors:
-
Hiroo Kitamura <hiroo.kitamura@ntt-at.co.jp>
Ai Hamano <ai.hamano@ntt-at.co.jp>
Work Items
- Implement availability zone reselection functions.
- Add new parameter
fallbackBestEffort
in GrantRequest API. - Add new definitions to the Tacker configuration file
tacker.conf
. - Add new unit and functional tests.
- Add new examples to the Tacker User Guide.
Dependencies
- VNF Lifecycle Operation Granting interface (Grant Lifecycle Operation)8
- VNF Lifecycle Management interface (Instantiate/Heal/Scale VNF)9
Testing
Unit and functional test cases will be added for the new placement functionalities.
Documentation Impact
New supported functions need to be added into the Tacker User Guide.
References
https://www.etsi.org/deliver/etsi_gs/NFV-SOL/001_099/003/03.03.01_60/gs_nfv-sol003v030301p.pdf↩︎
https://www.etsi.org/deliver/etsi_gs/NFV-SOL/001_099/003/03.03.01_60/gs_nfv-sol003v030301p.pdf↩︎
https://www.etsi.org/deliver/etsi_gs/NFV-SOL/001_099/003/03.03.01_60/gs_nfv-sol003v030301p.pdf↩︎
https://docs.openstack.org/api-ref/compute/?expanded=get-detailed-availability-zone-information-detail#availability-zones-os-availability-zone↩︎
https://docs.openstack.org/api-ref/identity/v3/?expanded=list-endpoints-detail#list-endpoints↩︎
https://docs.openstack.org/api-ref/identity/v3/?expanded=list-services-detail#list-services↩︎
https://docs.openstack.org/api-ref/orchestration/v1/index.html?expanded=show-stack-details-detail#show-stack-details↩︎
https://www.etsi.org/deliver/etsi_gs/NFV-SOL/001_099/003/03.03.01_60/gs_nfv-sol003v030301p.pdf↩︎
https://www.etsi.org/deliver/etsi_gs/NFV-SOL/001_099/003/03.03.01_60/gs_nfv-sol003v030301p.pdf↩︎