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September 8, 2019 ~ 2 min read

Labels and selectors


Labels are a set of key/pair values, used to attach to objects. Labels are designed to specify meaningful, identifying information for the object. Common usage is micro-service name, tier, environment, and software version. Users could define meaningful labels that could be used with selector later.

Labels syntax in object spec is:

labels:
    $key1: $value1 $key2: $value2

Along with label, label selector is used to filter the set of objects. Separated by commas, multiple requirements will be joined by the AND logical operator. There are two ways to filter:

  • Equality-based requirement: Equality-based requirement supports the operator of =, ==, and !=. For example, if selector is chapter=2,version!=0.1, the result will be object C. If requirement is version=0.1, the result will be object A and object B. If we write the requirement in supported object spec, it'll be as follows: yaml selector: $key1: $value1

  • Set-based requirement: Set-based requirement supports in, notin, and exists (for key only). For example, if requirement is chapter in (3, 4),version, then object A will be returned. If requirement is version notin (0.2), !author_info, the result will be object A and object B. The following is an example if we write to the object spec that supports set-based requirement:

selector:
    matchLabels: $key1: $value1 matchExpressions: {key: $key2, operator: In, values: [$value1, $value2]}

Sebastian BolaƱos

Hi, I'm Sebastian. I'm a software developer from Costa Rica. You can follow me on Twitter. I enjoy working on trustless systems.