VNF scaling¶
VNF resources in terms of CPU core and memory are hardcoded in VNFD template through image flavor settings. This result in either provisioning VNF for typical usage or for maximum usage. The former leads to service disruption when load exceeds provisioned capacity. And the later leads to underutilized resources and waste during normal system load. So tacker provides a way to seamlessly scale the number of VNFs on demand either manually or automatically.
TOSCA schema for scaling policy¶
Tacker defines TOSCA schema for the scaling policy as given below:
tosca.policies.tacker.Scaling:
derived_from: tosca.policies.Scaling
description: Defines policy for scaling the given targets.
properties:
increment:
type: integer
required: true
description: Number of nodes to add or remove during the scale out/in.
min_instances:
type: integer
required: true
description: Minimum number of instances to scale in.
max_instances:
type: integer
required: true
description: Maximum number of instances to scale out.
default_instances:
type: integer
required: true
description: Initial number of instances.
cooldown:
type: integer
required: false
default: 120
description: Wait time (in seconds) between consecutive scaling
operations. During the cooldown period, scaling action will be ignored
targets:
type: list
entry_schema:
type: string
required: true
description: List of Scaling nodes.
Sample TOSCA with scaling policy¶
Following TOSCA snippet shows the scaling policy used in VNFD, in which vdu1 and vdu2 are already defined VDUs.
policies:
- sp1:
type: tosca.policies.tacker.Scaling
description: Simple VDU scaling
targets: [vdu1, vdu2]
properties:
min_instances: 1
max_instances: 3
default_instances: 2
increment: 1
Deploying scaling TOSCA template using Tacker¶
Once OpenStack/Devstack along with Tacker has been successfully installed, deploy a sample scaling template from location given below: https://github.com/openstack/tacker/tree/master/samples/tosca-templates/vnfd
Refer the ‘Getting Started’ link below on how to create a VNFD and deploy a VNF: https://docs.openstack.org/tacker/latest/install/getting_started.html
How to scale VNF using CLI¶
Tacker provides following CLI for scaling.
- openstack vnf scale –vnf-id <vnf-id>
–vnf-name <vnf name> –scaling-policy-name <policy name> –scaling-type <type>
Here,
scaling-policy-name - Policy name defined in scaling VNFD
scaling-type - in or out
vnf-id - scaling VNF id
vnf-name - scaling VNF name
For example, to scale-out policy ‘sp1’ defined above, this cli could be used as below:
- openstack vnf scale –vnf-name sample-vnf
–scaling-policy-name sp1 –scaling-type out
How to scale VNF using REST API¶
Tacker provides following REST API for scaling.
POST on v1.0/vnfs/<vnf-id>/actions
with body
{“scale”: { “type”: “<type>”, “policy” : “<scaling-policy-name>”}}
Here,
scaling-policy-name - Policy name defined in scaling VNFD
scaling-type - in or out
vnf-id - scaling VNF id
Response http status codes:
202 - Accepted the request for doing the scaling operation
404 - Bad request, if given scaling-policy-name and type are invalid
500 - Internal server error, on scaling operation failed due to an error
401 - Unauthorized
VNF state transitions during scaling operation¶
During the scaling operation, the VNF will be moving in below state transformations:
ACTIVE -> PENDING_SCALE_IN -> ACTIVE
ACTIVE -> PENDING_SCALE_IN -> ERROR
ACTIVE -> PENDING_SCALE_OUT -> ACTIVE
ACTIVE -> PENDING_SCALE_OUT -> ERROR
Limitations¶
Following features are not supported with scaling:
Auto-scaling feature is supported only with alarm monitors and it does not work with other monitors such as ping, http_ping.
When VNF is modelled with scaling requirement in VNFD, any config management requirement in VNFD is not supported.
Scaling feature does not support to selectively choose the VDU as part of scaling.