Relationship between resources in Managed Service for Kubernetes
Kubernetes is an environment for managing containerized applications. Kubernetes provides mechanisms for interacting with clusters that can automate tasks like deploying, scaling, and managing applications in containers.
The main entity in the service is the Kubernetes cluster.
Kubernetes cluster
Kubernetes clusters consist of a master and one or more node groups. The master is responsible for managing the Kubernetes cluster. Containerized user applications are run on nodes.
The service fully controls the master and monitors the status and health of node groups. Users can manage nodes directly and configure Kubernetes clusters using the Yandex.Cloud management console and the Managed Service for Kubernetes CLI and API.
Warning
Groups of Kubernetes nodes require internet access for downloading images and components.
Internet access can be provided in the following ways:
- By assigning each node in the group a public IP address.
- Configuring a VM as a NAT instance.
- Enabling NAT to the internet.
Kubernetes clusters in the Yandex.Cloud infrastructure use the following resources:
| Resource | Amount | Comments |
|---|---|---|
| Subnet | 2 | Kubernetes reserves ranges of IP addresses to use for pods and services. |
| Public IP | N | The number N includes: * One public IP address for the NAT instance. * A public IP address assigned to each node in the group if you use one-to-one NAT technology. |
Master
Masters are components that manage Kubernetes clusters.
They run Kubernetes control processes that include the Kubernetes API server, scheduler, and main resource controllers. The master lifecycle is managed by the service when creating or deleting a Kubernetes cluster. The master is responsible for global solutions that are run on all Kubernetes cluster nodes. These include scheduling workloads (such as containerized applications), managing the lifecycle of workloads, and scaling.
There are two types of masters that differ by their location in availability zones:
-
Zonal: A master created in a subnet in one availability zone.
-
Regional: A master created and distributed in three subnets in each availability zone. If a zone becomes unavailable, the regional master remains functional.
Warning
The internal IP address of a regional master is only available within a single Yandex Virtual Private Cloud cloud network.
Node group
A node group is a group of VMs in a Kubernetes cluster that have the same configuration and run the user's containers.
Configuration
When you create a group of nodes, you can configure the following VM parameters:
- VM type.
- Type and number of cores (vCPU).
- Amount of memory (RAM) and disk space.
You can create groups with different configurations in a Kubernetes cluster and place them in different availability zones.
Connecting to group nodes
You can connect to nodes in a group via SSH. Learn more in Connecting to a node via SSH.
Pod
A pod is a request to run one or more containers on a group node. In a Kubernetes cluster, each pod has a unique IP address so that applications do not conflict when using ports.
Containers are described in pods via JSON or YAML objects.
Service
Service is an abstraction that provides network load balancing functions. Traffic rules are configured for a group of pods united by a set of labels.
By default, a service is only available within a specific Kubernetes cluster, but it can be public and receive requests from outside the Kubernetes cluster.
Namespace
A namespace is an abstraction that logically isolates Kubernetes cluster resources and distributes quotas to them. This is useful for isolating resources of different teams and projects in a single Kubernetes cluster.
Node labels
Node labels, node_labels are a mechanism for grouping nodes together in Kubernetes. You can use node labels to manage pod distribution across the nodes of a cluster. For more information, see the Kubernetes documentation.
Warning
Don't confuse node group cloud labels (labels) with Kubernetes node labels (node_labels) managed by Managed Service for Kubernetes.
We recommend managing all node labels via the Yandex Managed Service for Kubernetes API since, by default, when updating or changing a node group, some of the nodes are recreated with different names and some of the old ones are deleted. That's why labels added using the Kubernetes API may be lost. Conversely, using the Kubernetes API to delete labels created via the Managed Service for Kubernetes API has no effect since they will be restored.
Node labels can only be set when creating a node group. Each object can be assigned a set of node labels in the form of a key:value pair. Each key must be unique to an object.
Node label keys can consist of two parts: an optional prefix and a name separated by a /.
A prefix is an optional part of a key. Prefix requirements:
- It must be a DNS subdomain: a series of DNS tags separated by dots
.. - The maximum length is 253 characters.
- The last character must be followed by a
/.
A name is a required part of a key. Naming requirements:
- The length can be up to 63 characters.
- May contain lowercase Latin letters, numbers, hyphens, underscores, and periods.
- The first and the last characters must be a letter or number.
For managing node labels, see Managing Kubernetes cluster node labels.