How To Use Label Selectors to Identify Resources
- 24 Jun 2024
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How To Use Label Selectors to Identify Resources
- Updated on 24 Jun 2024
- 2 Minutes to read
- Contributors
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Background
Labels are a mechanism that allows you to associate meaningful and relevant attributes to resources in your Kubernetes environment. The labels you associate with resources can then be used to organize, categorize, and select those resources. Label selectors are the mechanism you use to select and filter resources based on their labels. Label selectors allow you to precisely identify specific subsets of resources by specifying criteria that match resource labels.
Label Selectors
Label selectors are a search/filter syntax used to identify a set of resources based on the labels associated with the resources. A label selector can consist of multiple requirements; each requirement must be comma-separated. The comma separator acts as a logical AND; when multiple requirements are specified, all must be satisfied. Label selectors are case-sensitive; case mismatches will exclude a resource from the filter result set.
There are two types of label selectors:
equality-based
set-based
Set-based requirements can be mixed with equality-based requirements in the same label selector to define the appropriate filtering constraints.
Equality-based label selectors
Equality- and inequality-based label selectors filter by directly using label key-value pairs. To be considered a match, resources must have all of the specified labels, but they can have additional labels that are not part of the filtering constraints. Supported operators include =, ==, and !=. The = and == both represent equality, while != represents inequality.
Examples
| Label Selector | Results |
|---|---|
environment=production | Identifies all resources with the environment=production label |
environment!=beta | Identifies all resources with an environment label that is not environment=beta |
app=shopping-cart | Identifies all resources with the app=shopping-cart label |
environment=production, app=shopping-cart | Identifies all resources with the environment=production label AND the app=shopping-cart label |
Set-based label selectors
Set-based label selectors allow for more complex queries by filtering keys according to a set of values. To be considered a match, resources must have labels that match the specified criteria, but they can have additional labels that are not part of the filtering constraints. Supported operators include in and notin; you can also search on just the key.
Examples
| Label Selector | Results |
|---|---|
environment in (production, qa) | Identifies all resources with an environment=production or an environment=qa label |
environment notin (beta) | Identifies all resources with an environment label that is not environment=beta |
app in (shopping-cart) | Identifies all resources with the app=shopping-cart label |
environment in (production), app in (shopping-cart) | Identifies all resources with the environment=production label AND the app=shopping-cart label |
tier | Identifies all resources with a tier label, regardless of the value |
More information
Kubernetes documentation: Labels and Selectors
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