Spot instances on CloudFerro Cloud

Spot instance is resource similar to Amazon EC2 Spot Instances or Google Spot VMs. In short, user is provided with unused computational resources for a discounted price but those resources can be terminated on a short time notice whenever on-demand usage increases. The main use case are ephemeral workflows which can deal with being terminated unexpectedly and/or orchestration platforms which can deal with forced scaling down of available resources e.g. Kubernetes clusters.

What We Are Going To Cover

How to create spot instances

Additional configuration via tags

What is the expected behaviour

Prerequisites

No. 1 Account

You need a CloudFerro Cloud hosting account with access to the Horizon interface: https://horizon.cloudferro.com

No. 2 Available exclusively on WAW3-2 cloud

When using spot instances, be sure to work only on WAW3-2 cloud:

No. 3 Using quotas and flavors

For quotas, see this article: Dashboard Overview Project Quotas And Flavors Limits on CloudFerro Cloud

No. 3 OpenStack CLI client

If you want to interact with CloudFerro Cloud cloud using OpenStack CLI client, you need to have it installed. Check one of these articles:

Once you have installed this piece of software, you need to authenticate to start using it: How to activate OpenStack CLI access to CloudFerro Cloud cloud using one- or two-factor authentication

To test whether the openstack command is working, list flavors:

openstack flavor list

This is the result and there is a group of spot. flavors, marked here in red rectangle:

No. 4 Creation of a new instance

A spot instance is an instance which is created in a normal way, say, as explained in this article: How to create a Linux VM and access it from Linux command line on CloudFerro Cloud save for the fact that in Step 3 of that article, you are choosing a flavor that starts with word spot.:

You can see the flavor when the instance is created:

How to create spot instances

The only prerequisite for an instance being a spot instance is the use of specific flavor. They are typically denoted as

spot.<name of non-spot flavor>

and have exactly the same parameters as their non-spot counterparts. Hence, user is able to just as easily schedule spot instance via Horizon and Openstack CLI. Additionally, one can confirm that a flavor is indeed a spot flavor by using openstack CLI. A command such as

openstack flavor show spot.hma.small -f json -c properties

should contain cf:spot.instance set to True.

Additional configuration via tags

Additionally, you can configure behaviour of spot instances when they are deleted. This is achieved by setting tags either on existing instances with

openstack server set --tag <tag_value> --os-compute-api-version 2.26 <instance name or uuid>

or by creating already tagged instances with

openstack server create (...) --tag <tag_value> --os-compute-api-version 2.52 <instance name or uuid>

Currently supported tags

callback_url:<url value>: This endpoint will be called some time before the spot instance is terminated. Query parameters can be provided, no escaping is required. More specifically, a POST request will be sent with body

{
"instance_uuid": <instance_uuid>,
"time_until_deletion" <time until deletion in seconds>
}

Note that call with time_until_deletion set to 0 will be made to confirm the instance deletion.

The expected behaviour of spot instances

Currently, spot instances use the same project quota as on-demand instances and, under normal circumstances, behave identically to their non-ephemeral counterparts. When resources in the cloud become tight, the behaviour changes as well – scheduling an on-demand instance might still be possible but scheduling a spot instance may become unavailable. This is to make sure that on-demand user’s experience is prioritized.

How to convert spot instance to on-demand instance

If you receive notification that a spot instance is about to be deleted, you can prevent it by resizing it to a normal on-demand instance. (Note that instead of paying reduced price for spot instances, you are back to paying normal price for on-demand instances.)

You can resize instance through Horizon:

With CLI, you can use a command like this:

openstack server resize INSTANCE_NAME FLAVOR_NAME

Additional commands of interest are:

openstack server resize --confirm INSTANCE_NAME
openstack server resize --revert INSTANCE_NAME
openstack server show INSTANCE_NAME

Shelving is not available for spot instances.