Setting Container Specifications

Scenario

UCS allows you to set resource limits for added containers during workload creation. You can apply for and limit the CPU and memory quotas used by each pod in the workload.

Meanings

The meanings of requests and limits for CPU and memory are as follows:

• Requests are the minimum guaranteed amount of a resource that is reserved for containers in a pod. If the node where the pod is running does not have enough of that resource, the containers fail to be created.
• Limits are the maximum amount of a resource to be used by containers. You can specify the resource limit for a container to prevent the container from using more of that resource than the limit you set or being evicted due to node resource exhaustion.

When creating a workload, you are advised to set the upper and lower limits of CPU and memory resources. If the upper and lower resource limits are not set for a workload, a resource leak of this workload will make resources unavailable for other workloads deployed on the same node. In addition, workloads that do not have upper and lower resource limits cannot be accurately monitored.

Configuration Description

• CPU quotas:

  Table 1 Description of CPU quotas

  Parameter	Description
  CPU request	Minimum number of CPU cores required by a container. Resources are scheduled for the container based on this value. The container can be scheduled to this node only when the total available CPU on the node is greater than or equal to the number of containerized CPU applications.
  CPU limit	Maximum number of CPU cores available for a container.

  Recommended configuration

  Actual available CPU of a node ≥ Sum of CPU limits of all containers on the current node ≥ Sum of CPU requests of all containers on the current node. You can view the actual available CPUs of a node on the CCE console (Resource Management > Nodes > Allocatable).

• Memory quotas:

  Table 2 Description of memory quotas

  Parameter	Description
  Memory request	Minimum amount of memory required by a container. Resources are scheduled for the container based on this value. The container can be scheduled to this node only when the total available memory on the node is greater than or equal to the number of containerized memory applications.
  Memory Limit	Maximum amount of memory available for a container. When the memory usage exceeds the configured memory limit, the instance may be restarted, which affects the normal use of the workload.

  Recommended configuration

  Actual available memory of a node ≥ Sum of memory limits of all containers on the current node ≥ Sum of memory requests of all containers on the current node. You can view the actual available memory of a node on the CCE console (Resource Management > Nodes > Allocatable).

The allocatable resources are calculated based on the resource request value (Request), which indicates the upper limit of resources that can be requested by pods on this node, but does not indicate the actual available resources of the node. The calculation formula is as follows:

• Allocatable CPU = Total CPU – Requested CPU of all pods – Reserved CPU for other resources
• Allocatable memory = Total memory – Requested memory of all pods – Reserved memory for other resources

Example

Assume that a cluster contains a node with 4 cores and 8 GB. A workload containing two pods has been deployed on the cluster. The resources of the two pods (pods 1 and 2) are as follows: {CPU request, CPU limit, memory request, memory limit} = {1 core, 2 cores, 2 GB, 2 GB}.

The CPU and memory usage of the node is as follows:

• Allocatable CPU = 4 cores - (1 core requested by pod 1 + 1 core requested by pod 2) = 2 cores
• Allocatable memory = 8 GB - (2 GB requested by pod 1 + 2 GB requested by pod 2) = 4 GB

Therefore, the remaining 2 cores and 4 GB can be used by the next new pod.