Deployment Limits for Red Hat OpenStack Platform

Updated 4 Oct 2023

These limits for Red Hat OpenStack Platform components can be used to help design and scale OpenStack deployments. For more information on configuration options, see Recommended Practices for OpenStack, and the OpenStack documentation.

Networking service (Neutron)

Area	Maximum Limit	Notes
Number of logical networks in the environment using VLAN	4,094	This is the number of unique networks when using VLANs (12-bit VID in 802.1q).
Number of logical networks in the environment using NVGRE / VXLAN	16,000,000	This is the number of unique networks when using NVGRE (24-bit TNI) or VXLAN (24-bit VNI).
Number of logical networks per compute node	4,094	This assumes that you are using the ML2/Open vSwitch plugin. OVS 'br-int' uses local VLANs to separate traffic on the node.
Number of logical networks served by a network node	4,094	This assumes that you are using the ML2/Open vSwitch plugin. OVS 'br-int' uses local VLANs to separate traffic on the node.
Number of external networks	Topology-dependent	The maximum limit is the sum of the logical networks served by a network node or compute node, if OpenStack is set as a provider network on the compute node.
Number of routed networks	Unlimited
Number of HA routers	255 per tenant	The number of HA routers per tenant is capped to 255 due to the VRRP protocol. Also, there is a limit on the maximum number of HA routers across all tenants based on the memory available on the overcloud controllers as each HA router created, spawns a neutron-keepalived-state-change process which consumes 85M of RSS memory.
Number of gateways	Unlimited	Some versions of Open vSwitch limit the number of namespaces to 1,000. This can impact the number of gateways.
Number of network pools	Unlimited
Number of load balancers	Unlimited	This is limited by the number of processes you can start on the machine. Some versions of Open vSwitch limit the number of namespaces to 1,000. This can impact the number of load balancers. Also in the case of Octavia with amphora driver, a VM with HAProxy acts as the load balancer, so you could also be limited by the capacity on the hypervisors.

Compute service (Nova)

Area	Maximum Limit	Notes
Number of virtual machines per KVM host	16384	This is limited by the operating system limits for process counts and open files.
Allocated RAM per KVM host	64TB	For more information, see Red Hat Enterprise Linux technology capabilities and limits.
Number of virtual CPUs per virtual machine	160, 240, 288, or 710	The limit was raised to 710 in RHEL 8. For RHEL 7.3, the limit is 288. For RHEL 7.1 and RHEL 7.2, the limit is 240. In previous versions of RHEL, the limit is 160. For more information, see Virtualization limits for Red Hat Enterprise Linux with KVM.
RAM per virtual machine	4000GB	For more information, see Virtualization limits for Red Hat Enterprise Linux with KVM.
Virtual machine swap file size	System limits	The limit is the available disk space.
Virtual NICs per virtual machine	28	This is determined by the number of used PCI slots and the number of available slots (depends on QEMU machine type). If there are 32 slots (pc-i440fx* machine types), then slots are allocated for video, PIIX, balloon, and disk, which leaves 28 slots for NICs; if other slots are active, then the maximum number may be lower than 28. If NICs are being assigned as vfio devices, then RHEL8 has a limit of 64 devices for pc-i440fx* machine types. Note that there is no set limit on the number of NICs if the hw_machine_type is q35, but creating too many NICs may cause CPU pressure depending on the number of CPUs that are assigned or cause a timeout trying to start up and configure a large number of NICs at boot time.
Video memory per virtual machine	Driver-dependent	Different drivers have different performance limits.
Concurrent remote console connections to a virtual machine	65000	Limited by the number of TCP ports available that can opened against any single IP address. This will be something less than 65535 per compute host. Since a single console server targets many hosts, you'll in fact have a 65536 concurrent connection limit across everything served by that nova console host
Serial ports per virtual machine	2
Serial ports per virtual machine with virtio-console	Many
Number of cells per region	8	Multiple-cells Cells V2 is supported.
Number of instances	No known tested limit	There is no limit on the number of instances in a cloud, but the sizing of the environment, including controllers, can affect the practical limit.
Number of hosts	700	There is no theoretical limit on the number of hosts in a cloud, but the sizing of the environment, including controllers, can affect the practical limit. Red Hat doesn't support scaling more than 700 hosts on a single director. This is supported from RHOSP16.1 or later. For RHOSP13, we only support 500 hosts.

Image service (Glance)

Area	Maximum Limit	Notes
Number of images	Unlimited	The practical limit depends on the underlying database performance and back end storage type.

Orchestration service / Template (Heat)

Area	Maximum Limit	Notes
Number of templates	Relative to projects	The number of templates is related to the number of projects. With the default settings, there can be no more than 100 * the number of projects.
Number of virtual machines per template	1,000	This is a default configuration setting.
Number of templates per project	100	This is a default configuration setting.

Block Storage service (Cinder)

Area	Maximum Limit	Notes
Number of volumes	Unlimited	Specific databases may have relevant performance limits. No limits are imposed through the OpenStack configuration.
Number of concurrent active volumes	Unlimited	This is the control path component. The prospective volume is the raw database. The storage database may have limits on the number of active volumes.
Number of independent disks	Unlimited
Number of unique storage classes	Unlimited
Number of back end storage classes	Unlimited
Number of mounted volumes per host	Unlimited	For iSCSI/FC: 10,000 devices on the system. 1024 paths per multipath group and up to 1024 multipath groups. Depending on the storage backend, cinder driver, HBA driver, etc. additional limits may be in place.
Number of mounted volumes per virtual machine	Unlimited	For RHOSP13z10 and earlier, the maximum is 26 volumes. For RHOSP13z11 and later, the theoretical maximum is unlimited if using virtio-scsi. While there is no theoretical limit on the maximum number of attached volumes in RHOSP13z11 and later, physical limitations can come from: the disk bus, the hypervisor, the host OS, or the storage backend.

Identity service (Keystone)

Area	Maximum Limit	Notes
Number of regions	Unlimited	There is no technical limit within OpenStack, but overall performance depends primarily on the underlying database performance.
Total number of users	Unlimited	There is no technical limit within OpenStack, but overall performance depends primarily on the underlying database performance.
Number of projects	Unlimited	There is no technical limit within OpenStack, but overall performance depends primarily on the underlying database performance.
Number of users per project	Unlimited	There is no technical limit within OpenStack, but overall performance depends primarily on the underlying database performance.
Number of active concurrent users	Unlimited	There is no technical limit within OpenStack, but other practical performance limits apply.