PLEASE NOTE: This document applies to the HEAD of the source tree
If you are using a released version of Kubernetes, you should
refer to the docs that go with that version.
The latest release of this document can be found
[here](http://releases.k8s.io/release-1.1/docs/design/admission_control_limit_range.md).
Documentation for other releases can be found at
[releases.k8s.io](http://releases.k8s.io).
--
# Admission control plugin: LimitRanger
## Background
This document proposes a system for enforcing resource requirements constraints as part of admission control.
## Use cases
1. Ability to enumerate resource requirement constraints per namespace
2. Ability to enumerate min/max resource constraints for a pod
3. Ability to enumerate min/max resource constraints for a container
4. Ability to specify default resource limits for a container
5. Ability to specify default resource requests for a container
6. Ability to enforce a ratio between request and limit for a resource.
## Data Model
The **LimitRange** resource is scoped to a **Namespace**.
### Type
```go
// LimitType is a type of object that is limited
type LimitType string
const (
// Limit that applies to all pods in a namespace
LimitTypePod LimitType = "Pod"
// Limit that applies to all containers in a namespace
LimitTypeContainer LimitType = "Container"
)
// LimitRangeItem defines a min/max usage limit for any resource that matches on kind.
type LimitRangeItem struct {
// Type of resource that this limit applies to.
Type LimitType `json:"type,omitempty"`
// Max usage constraints on this kind by resource name.
Max ResourceList `json:"max,omitempty"`
// Min usage constraints on this kind by resource name.
Min ResourceList `json:"min,omitempty"`
// Default resource requirement limit value by resource name if resource limit is omitted.
Default ResourceList `json:"default,omitempty"`
// DefaultRequest is the default resource requirement request value by resource name if resource request is omitted.
DefaultRequest ResourceList `json:"defaultRequest,omitempty"`
// MaxLimitRequestRatio if specified, the named resource must have a request and limit that are both non-zero where limit divided by request is less than or equal to the enumerated value; this represents the max burst for the named resource.
MaxLimitRequestRatio ResourceList `json:"maxLimitRequestRatio,omitempty"`
}
// LimitRangeSpec defines a min/max usage limit for resources that match on kind.
type LimitRangeSpec struct {
// Limits is the list of LimitRangeItem objects that are enforced.
Limits []LimitRangeItem `json:"limits"`
}
// LimitRange sets resource usage limits for each kind of resource in a Namespace.
type LimitRange struct {
TypeMeta `json:",inline"`
// Standard object's metadata.
// More info: http://releases.k8s.io/HEAD/docs/devel/api-conventions.md#metadata
ObjectMeta `json:"metadata,omitempty"`
// Spec defines the limits enforced.
// More info: http://releases.k8s.io/HEAD/docs/devel/api-conventions.md#spec-and-status
Spec LimitRangeSpec `json:"spec,omitempty"`
}
// LimitRangeList is a list of LimitRange items.
type LimitRangeList struct {
TypeMeta `json:",inline"`
// Standard list metadata.
// More info: http://releases.k8s.io/HEAD/docs/devel/api-conventions.md#types-kinds
ListMeta `json:"metadata,omitempty"`
// Items is a list of LimitRange objects.
// More info: http://releases.k8s.io/HEAD/docs/design/admission_control_limit_range.md
Items []LimitRange `json:"items"`
}
```
### Validation
Validation of a **LimitRange** enforces that for a given named resource the following rules apply:
Min (if specified) <= DefaultRequest (if specified) <= Default (if specified) <= Max (if specified)
### Default Value Behavior
The following default value behaviors are applied to a LimitRange for a given named resource.
```
if LimitRangeItem.Default[resourceName] is undefined
if LimitRangeItem.Max[resourceName] is defined
LimitRangeItem.Default[resourceName] = LimitRangeItem.Max[resourceName]
```
```
if LimitRangeItem.DefaultRequest[resourceName] is undefined
if LimitRangeItem.Default[resourceName] is defined
LimitRangeItem.DefaultRequest[resourceName] = LimitRangeItem.Default[resourceName]
else if LimitRangeItem.Min[resourceName] is defined
LimitRangeItem.DefaultRequest[resourceName] = LimitRangeItem.Min[resourceName]
```
## AdmissionControl plugin: LimitRanger
The **LimitRanger** plug-in introspects all incoming pod requests and evaluates the constraints defined on a LimitRange.
If a constraint is not specified for an enumerated resource, it is not enforced or tracked.
To enable the plug-in and support for LimitRange, the kube-apiserver must be configured as follows:
```console
$ kube-apiserver --admission-control=LimitRanger
```
### Enforcement of constraints
**Type: Container**
Supported Resources:
1. memory
2. cpu
Supported Constraints:
Per container, the following must hold true
| Constraint | Behavior |
| ---------- | -------- |
| Min | Min <= Request (required) <= Limit (optional) |
| Max | Limit (required) <= Max |
| LimitRequestRatio | LimitRequestRatio <= ( Limit (required, non-zero) / Request (required, non-zero)) |
Supported Defaults:
1. Default - if the named resource has no enumerated value, the Limit is equal to the Default
2. DefaultRequest - if the named resource has no enumerated value, the Request is equal to the DefaultRequest
**Type: Pod**
Supported Resources:
1. memory
2. cpu
Supported Constraints:
Across all containers in pod, the following must hold true
| Constraint | Behavior |
| ---------- | -------- |
| Min | Min <= Request (required) <= Limit (optional) |
| Max | Limit (required) <= Max |
| LimitRequestRatio | LimitRequestRatio <= ( Limit (required, non-zero) / Request (non-zero) ) |
## Run-time configuration
The default ```LimitRange``` that is applied via Salt configuration will be updated as follows:
```
apiVersion: "v1"
kind: "LimitRange"
metadata:
name: "limits"
namespace: default
spec:
limits:
- type: "Container"
defaultRequests:
cpu: "100m"
```
## Example
An example LimitRange configuration:
| Type | Resource | Min | Max | Default | DefaultRequest | LimitRequestRatio |
| ---- | -------- | --- | --- | ------- | -------------- | ----------------- |
| Container | cpu | .1 | 1 | 500m | 250m | 4 |
| Container | memory | 250Mi | 1Gi | 500Mi | 250Mi | |
Assuming an incoming container that specified no incoming resource requirements,
the following would happen.
1. The incoming container cpu would request 250m with a limit of 500m.
2. The incoming container memory would request 250Mi with a limit of 500Mi
3. If the container is later resized, it's cpu would be constrained to between .1 and 1 and the ratio of limit to request could not exceed 4.
[]()