Object Names and IDs

Each object in your cluster has a Name that is unique for that type of resource. Every Kubernetes object also has a UID that is unique across your whole cluster.

For example, you can only have one Pod named myapp-1234 within the same namespace, but you can have one Pod and one Deployment that are each named myapp-1234.

For non-unique user-provided attributes, Kubernetes provides labels and annotations.

Names

A client-provided string that refers to an object in a resource URL, such as /api/v1/pods/some-name.

Only one object of a given kind can have a given name at a time. However, if you delete the object, you can make a new object with the same name.

Note: In cases when objects represent a physical entity, like a Node representing a physical host, when the host is re-created under the same name without deleting and re-creating the Node, Kubernetes treats the new host as the old one, which may lead to inconsistencies.

Below are four types of commonly used name constraints for resources.

DNS Subdomain Names

Most resource types require a name that can be used as a DNS subdomain name as defined in RFC 1123. This means the name must:

  • contain no more than 253 characters
  • contain only lowercase alphanumeric characters, ‘-‘ or ‘.’
  • start with an alphanumeric character
  • end with an alphanumeric character

RFC 1123 Label Names

Some resource types require their names to follow the DNS label standard as defined in RFC 1123. This means the name must:

  • contain at most 63 characters
  • contain only lowercase alphanumeric characters or ‘-‘
  • start with an alphanumeric character
  • end with an alphanumeric character

RFC 1035 Label Names

Some resource types require their names to follow the DNS label standard as defined in RFC 1035. This means the name must:

  • contain at most 63 characters
  • contain only lowercase alphanumeric characters or ‘-‘
  • start with an alphabetic character
  • end with an alphanumeric character

Path Segment Names

Some resource types require their names to be able to be safely encoded as a path segment. In other words, the name may not be “.” or “..” and the name may not contain “/“ or “%”.

Here’s an example manifest for a Pod named nginx-demo.

  1. apiVersion: v1
  2. kind: Pod
  3. metadata:
  4.   name: nginx-demo
  5. spec:
  6.   containers:
  7.   - name: nginx
  8.     image: nginx:1.14.2
  9.     ports:
  10.     - containerPort: 80

Note: Some resource types have additional restrictions on their names.

UIDs

A Kubernetes systems-generated string to uniquely identify objects.

Every object created over the whole lifetime of a Kubernetes cluster has a distinct UID. It is intended to distinguish between historical occurrences of similar entities.

Kubernetes UIDs are universally unique identifiers (also known as UUIDs). UUIDs are standardized as ISO/IEC 9834-8 and as ITU-T X.667.

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