# Constraint In Juju, a **constraint** is a key-value pair that represents a specification that can be passed to certain `juju` commands /command flags to customise the [compute resources](https://documentation.ubuntu.com/juju/2.9/reference/resource-compute.md#resource-compute) (bare metal machines, virtual machines, system containers, Kubernetes containers) spawned by Juju. If the resource is a bare metal machine or a virtual machine, a constraint represents a minimum, whereas if the resource is a system container or a Kubernetes container it represents a maximum. For machine (non-Kubernetes) clouds, constraints can be set directly on individual [machines](https://documentation.ubuntu.com/juju/2.9/reference/machine.md#machine). However, more commonly they are set at the level of the [controller](https://documentation.ubuntu.com/juju/2.9/reference/controller.md#controller), [model](https://documentation.ubuntu.com/juju/2.9/reference/model.md#model), or [application](https://documentation.ubuntu.com/juju/2.9/reference/application.md#application). If you set constraints at multiple levels at once – that is, with overlap – the constraint applied at the more specific level takes precedence. The rest of this document describes all the existing constraints. #### CAUTION Some of these keys – their availability and their meaning – vary from one cloud to another. Below this is indicated with a generic note. For specifics see [List of supported clouds](https://documentation.ubuntu.com/juju/2.9/reference/cloud/list-of-supported-clouds.md#list-of-supported-clouds) > ``. ## List of constraints ## `allocate-public-ip` Supplying this constraint will determine whether machines are issued an IP address accessible outside of the cloud’s virtual network.

**Valid values:** `true`, `false`.

**Note:** Applies to public clouds (GCE, EC2, Azure) and OpenStack. Public cloud instances are assigned a public IP by default. ## `arch` The architecture.

**Valid values:** `amd64`, `arm64`, `ppc64el`, `s390x`, `riscv64`. ## `container` Indicates that a machine must be the specified container type.

**Valid values:** `lxd`, `kvm`. ## `cores` Number of effective CPU cores.

**Type:** integer.

**Alias:** `cpu-cores`. ## `cpu-power` Abstract CPU power.

**Type:** integer, where 100 units is roughly equivalent to “a single 2007-era Xeon” as reflected by 1 Amazon vCPU. In a Kubernetes context a unit of “milli” is implied.

**Note:** Not supported by all providers. Use `cores` for portability. ## `image-id` |

`image-id`

| (Starting with `3.2`) The image ID. If not nil, indicates that a machine must use the specified image.

**Note:** Not supported by all providers. Value is provider-specific. Also, when applied during `juju deploy`, must be used in conjunction with the `--base` flag of the command – the `image-id` will specify the image to be used for the provisioned machines and the `--base` will specify the charm revision to be deployed on those machines. | ## `instance-role` Indicates that the specified role/profile for the given cloud should be used.

**Note:** Only valid for clouds which support instance roles. Currently only for AWS with instance profiles and (starting with Juju 3.6) for Azure with managed identities. ## `instance-type` Cloud-specific instance-type name. Values vary by provider, and individual deployment in some cases.

**Note:** When compatibility between clouds is desired, use corresponding values for `cores`, `mem`, and `root-disk` instead. ## `mem` Memory (MiB). An optional suffix of M/G/T/P indicates the value is mega-/giga-/tera-/peta- bytes. ## `root-disk` Disk space on the root drive (MiB). An optional suffix of M/G/T/P is used as per the `mem` constraint. Additional storage that may be attached separately does not count towards this value. ## `root-disk-source` Name of the storage pool or location the root disk is from.

**Note:** `root-disk-source` has different behaviour with each provider. ## `spaces` A comma-delimited list of Juju network space names that a unit or machine needs access to. Space names can be positive, listing an attribute of the space, or negative (prefixed with “^”), listing something the space does not have.

Example: `spaces=storage,db,^logging,^public` (meaning, select machines connected to the storage and db spaces, but NOT to logging or public spaces).

**Note:** EC2 and MAAS are the only providers that currently support the spaces constraint. ## `tags` Comma-delimited tags assigned to the machine. Tags can be positive, denoting an attribute of the machine, or negative (prefixed with `^`), to denote something that the machine does not have.

Example: `tags=virtual,^dualnic`

**Note:** Currently only supported by the MAAS provider. ## `virt-type` Virtualisation type.

**Valid values:** `kvm`, `virtual-machine`. ## `zones` A list of availability zones. Multiple values present a range of zones that a machine must be created within.

**Valid values:** Depending on the cloud provider.

**Example for the `aws` cloud:** `zones=us-east-1a,us-east-1c`

**Note:** A zone can also be used as a [placement directive](https://documentation.ubuntu.com/juju/2.9/reference/placement-directive.md#placement-directive) (`--to zone= `).