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-title: Using AWS Spot instances
+title: Using Preemptible instances
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SPDX-License-Identifier: CC-BY-SA-3.0
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-This page describes how to set up the system to take advantage of "Amazon's EC2 spot instances":https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-spot-instances.html.
+This page describes how to enable preemptible instances. Preemptible instances typically offer lower cost computation with a tradeoff of lower service guarantees. If a compute node is preempted, Arvados will restart the computation on a new instance.
-h3. Nodemanager
+Currently Arvados supports preemptible instances using AWS and Azure spot instances.
-Nodemanager should have configured cloud sizes that include the @preemptible@ boolean parameter. For example, for every on-demand cloud node size, you could create a @.spot@ variant, like this:
+h2. Configuration
-<pre>
-[Size m4.large]
-cores = 2
-scratch = 32000
-
-[Size m4.large.spot]
-cores = 2
-instance_type = m4.large
-preemptible = true
-scratch = 32000
-</pre>
-
-h3. Slurm dispatcher
-
-The @crunch-dispatch-slurm@ service needs a matching instance type configuration on @/etc/arvados/config.yml@, following the previous example:
+To use preemptible instances, set @UsePreemptibleInstances: true@ and add entries to @InstanceTypes@ with @Preemptible: true@ to @config.yml@. Typically you want to add both preemptible and non-preemptible entries for each cloud provider VM type. The @Price@ for preemptible instances is the maximum bid price, the actual price paid is dynamic and will likely be lower. For example:
<pre>
Clusters:
- uuid_prefix:
+ ClusterID:
+ Containers:
+ UsePreemptibleInstances: true
InstanceTypes:
- - Name: m4.large
- VCPUs: 2
- RAM: 7782000000
- Scratch: 32000000000
- Price: 0.1
- - Name: m4.large.spot
- Preemptible: true
- VCPUs: 2
- RAM: 7782000000
- Scratch: 32000000000
- Price: 0.1
+ m4.large:
+ Preemptible: false
+ ProviderType: m4.large
+ VCPUs: 2
+ RAM: 8GiB
+ AddedScratch: 32GB
+ Price: 0.1
+ m4.large.spot:
+ Preemptible: true
+ ProviderType: m4.large
+ VCPUs: 2
+ RAM: 8GiB
+ AddedScratch: 32GB
+ Price: 0.1
</pre>
-@InstanceType@ names should match those defined on nodemanager's config file because it's @crunch-dispatch-slurm@'s job to select the instance type and communicate the decision to @nodemanager@ via Slurm.
+When @UsePreemptibleInstances@ is enabled, child containers (workflow steps) will automatically be made preemptible. Note that because preempting the workflow runner would cancel the entire workflow, the workflow runner runs in a reserved (non-preemptible) instance.
-h3. API Server
+No additional configuration is required, "arvados-dispatch-cloud":{{site.baseurl}}/install/crunch2-cloud/install-dispatch-cloud.html will now start preemptible instances where appropriate.
-Container requests will need the @preemptible@ scheduling parameter included, to make the dispatcher request a spot instance. The API Server configuration file includes an option that when active, will auto assign the @preemptible@ parameter to any new child container request if it doesn't have it already. To activate this feature, the following should be added to the @application.yml@ file:
+h3. Cost Tracking
-<pre>
-preemptible_instances: true
-</pre>
+Preemptible instances prices are declared at instance request time and defined by the maximum price that the user is willing to pay per hour. By default, this price is the same amount as the on-demand version of each instance type, and this setting is the one that @arvados-dispatch-cloud@ uses for now, as it doesn't include any pricing data to the spot instance request.
+
+For AWS, the real price that a spot instance has at any point in time is discovered at the end of each usage hour, depending on instance demand. For this reason, AWS provides a data feed subscription to get hourly logs, as described on "Amazon's User Guide":https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/spot-data-feeds.html.
+
+h2. Preemptible instances on AWS
-With this configuration active, child container requests should include the @preemptible = false@ parameter at creation time to avoid being scheduled for spot instance usage.
+For general information, see "using Amazon EC2 spot instances":https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-spot-instances.html.
-h3. AWS Permissions
+h3. Permissions
-When requesting spot instances, Amazon's API may return an authorization error depending on how users and permissions are set on the account. If this is the case check nodemanager's log for:
+When requesting spot instances, Amazon's API may return an authorization error depending on how users and permissions are set on the account. If this is the case check logs for this error:
<pre>
BaseHTTPError: AuthFailure.ServiceLinkedRoleCreationNotPermitted: The provided credentials do not have permission to create the service-linked role for EC2 Spot Instances.
The account needs to have a service linked role created. This can be done by logging into the AWS account, go to _IAM Management_ → _Roles_ and create the @AWSServiceRoleForEC2Spot@ role by clicking on the @Create@ button, selecting @EC2@ service and @EC2 - Spot Instances@ use case.
-h3. Cost Tracking
+h2. Preemptible instances on Azure
+
+For general information, see "Use Spot VMs in Azure":https://docs.microsoft.com/en-us/azure/virtual-machines/spot-vms.
+
+When starting preemptible instances on Azure, Arvados configures the eviction policy to 'delete', with max price set to '-1'. This has the effect that preemptible VMs will not be evicted for pricing reasons. The price paid for the instance will be the current spot price for the VM type, up to a maximum of the price for a standard, non-spot VM of that type.
-Amazon's Spot instances prices are declared at instance request time and defined by the maximum price that the user is willing to pay per hour. By default, this price is the same amount as the on-demand version of each instance type, and this setting is the one that nodemanager uses for now, as it doesn't include any pricing data to the spot instance request.
+Please note that Azure provides no SLA for preemptible instances. Even in this configuration, preemptible instances can still be evicted for capacity reasons. If that happens and a container is aborted, Arvados will try to restart it, subject to the usual retry rules.
-The real price that a spot instance has at any point in time is discovered at the end of each usage hour, depending on instance demand. For this reason, AWS provides a data feed subscription to get hourly logs, as described on "Amazon's User Guide":https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/spot-data-feeds.html.
\ No newline at end of file
+Spot pricing is not available on 'B-series' VMs, those should not be defined in the configuration file with the _Preemptible_ flag set to true. Spot instances have a separate quota pool, make sure you have sufficient quota available.
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