Reserved instance pools

The reserved instance pool feature is at the Preview stage.

A reserved instance pool is the total of computing resources reserved by the user in a given availability zone to secure their guaranteed availability to the user for the purpose of creating VMs of a particular configuration in this availability zone.

You can manage reserved instance pools and attach VMs to them using the Yandex Cloud CLI and API.

Reserved instance pools are incompatible with dedicated hosts, preemptible VMs, and VMs with vCPU performance levels below 100%. At present, reserved instance pools do not support placement groups and instance groups.

A reserved instance pool consists of a set of slots, i.e., collections of the availability zone's computing resources that are minimally required to launch one VM in the configuration specified for the pool.

Pool sizePool size

The size of a reserved instance pool is the number of its slots. You can view a pool’s size in its details.

When modifying the size of a pool with pending slots, another key parameter apart from size will be its committed_size. The committed_size field indicates the actual number of non-pending slots in the pool, i.e., the number of slots for which Compute Cloud guarantees resources.

A pool’s committed_size will be different from its size only if the pool has pending slots. If pending slots are not used, the pool’s committed_size will match its size.

Each running VM attached to a reserved instance pool occupies a single slot. VMs attached to the pool but not currently running do not occupy any slots but still count towards the total number of VMs in the pool.

In pools with overcommitment disabled, the number of attached VMs cannot exceed the committed_size value. To attach more VMs to a pool than specified as its committed_size, enable overcommitment.

Regardless of the overcomminment state, the number of VMs you can run simultaneously cannot exceed the committed_size value.

Pending slotsPending slots

When increasing the size of a pool, you can enable the pending slots option. This allows you to add to the pool as many slots as you need even if the pool's availability zone currently lacks resources to accommodate them.

You can manage this setting via --allow-pending-slots in the yc compute reserved-instance-pool update Yandex Cloud CLI command or in the allow_pending_slots field of an API request.

When you scale up a pool with pending slots enabled, and there are not enough resources to create new slots immediately, any such slots will get the pending status. Yandex Compute Cloud will continuously search for resources in the reserved instance pool's availability zone to allocate them to pending slots. Once there are enough resources for a slot, its status changes to available, and the pool's committed_size value increases accordingly.

You must enable pending slots each time you change the size of a pool with slots in the pending status. Otherwise, the reserved instance pool update operation will fail. The only exception is scaling a pool down to a value that does not exceed its committed_size. When you scale down a pool, its pending slots will be removed first.

Creating a poolCreating a pool

When creating a reserved instance pool, you specify its size as the number of slots, the availability zone the computing resources will be reserved in, and the configuration of the virtual machines in the pool.

The configuration of VMs in the pool includes the following parameters:

• Platform
• Number of vCPUs
• Amount of RAM
• Cluster and number of GPUs
• Network type (standard or software-accelerated)

You can change the pool size after you create it. The availability zone and VM configuration are set when you create a pool and cannot be changed later.

Managing instances in a poolManaging instances in a pool

Attaching VMs to a poolAttaching VMs to a pool

To attach a virtual machine to a reserved instance pool, provide the pool ID in the VM’s settings. You can attach a VM to a reserved instance pool either when creating a new VM or when updating an existing one.

When you create a new virtual machine in the reserved instance pool, this virtual machine will occupy one of the free slots in the pool. If you create a VM in a pool with no free slots, the VM creation will fail with an error. To fix this, you can increase the pool size.

When attaching an existing virtual machine to a reserved instance pool:

• If the VM is stopped, the total value in the pool's VM statistics will increase.

• If the VM is running, the number of available slots in the pool's slot statistics will decrease while the number of used slots will increase as well as the total value in the VM statistics.

  If the pool has pending or unavailable slots, the running VMs you are attaching will replace such slots first, starting with unavailable ones.

By default, the number of VMs attached to a pool cannot exceed its actual size, specified under committed_size. The possible workaround is to use overcommitment.

OvercommitmentOvercommitment

In overcommitment mode, you can attach any number of stopped VMs to a pool so that the total count of attached VMs can exceed its size. However, the number of simultaneously running VMs in a pool cannot be more than its current committed_size, which means an attempt to start a VM in a pool with no available slots will fail.

You can enable overcommitment when creating or updating a reserved instance pool by using the --allow-oversubscription parameter in these Yandex Cloud CLI commands: yc compute reserved-instance-pool create|update. Alternatively, use the allow_oversubscription field in the API request.

To disable overcommitment in a pool, make sure the number of attached VMs does not exceed its committed_size. Remember to detach any excess VMs first.

Starting and stopping VMs attached to a poolStarting and stopping VMs attached to a pool

Stopping a VM attached to a reserved instance pool releases the slot occupied by that VM, changing the slot's status back to available. The released slot can then be used by the same or another VM in the pool. This means stopped VMs do not consume slots in reserved instance pools.

When restarted, this VM will again occupy one of the available slots, switching it back to used.

Detaching VMs from a poolDetaching VMs from a pool

You can detach a virtual machine from a reserved instance pool:

• If the VM is stopped, the total value in the pool's VM statistics decreases.

• If the VM is running, the number of available slots in the pool's slot statistics increases while the number of used slots as well as the total value in the VM statistics decreases.

  You can detach a running VM from a pool only if the availability zone has resources to reserve for the slot being released.

  Note

  Detaching a running VM from a reserved instance pool increases the amount of billable resources: you pay for the detached VM separately from the pool as well as the resources reserved for its new available slot.

Statistics of pool resource usageStatistics of pool resource usage

To get information about a reserved instance pool, use the yc compute reserved-instance-pool get Yandex Cloud CLI command, the get REST API method for the ReservedInstancePool resource, or the ReservedInstancePoolService/Get gRPC API call. The output will return the pool's name, ID, size, availability zone, configuration of its VMs, slot and VM statistics, as well as other properties.

Pool slot statisticsPool slot statistics

In slot statistics of a reserved instance pool, the following fields are available:

• total: Total number of slots in the pool. This is the sum of all used, available, unavailable, and pending slots.

• used: Number of slots currently occupied by running VMs.

• available: Number of slots which have reserved resources in the pool's availability zone. These slots can be occupied by VMs.

  All available slots in a reserved instance pool use up quotas for the total number of vCPUs, GPUs, and VM's total virtual memory but do not use up quotas for the number of VMs per cloud.

• unavailable: Number of slots currently unavailable due to technical issues.

  If some of the hardware allocated to the pool fails, a slot may become unavailable. You cannot use such a slot to run a VM.

  Compute Cloud continuously attempts to restore unavailable slots using the availability zone’s resources. Once the required resources are found, the slot’s status changes back to available.

• pending: Number of pending slots.

  This status is assigned to a new slot when you scale up a pool and the availability zone lacks resources to allocate to this new slot, provided you perform the update with the pending slots setting enabled.

  Compute Cloud continuously searches for resources to allocate them to pending slots. Once it finds sufficient resources for a slot, its status changes to available.

Pool VM statisticsPool VM statistics

The VM statistics indicate the total number of virtual machines attached to a reserved instance pool. This value represents all its attached VMs, both running and stopped.

Deleting a poolDeleting a pool

When you delete a reserved instance pool, all VMs attached to it will be detached, and the running ones will continue to operate.

See alsoSee also

• Creating a reserved instance pool
• Updating a reserved instance pool
• Deleting a reserved instance pool
• Managing VMs in a reserved instance pool