In the following, one component template and an index template are created. The index template references two component templates, but only the @package one exists.

Create the component template logs-foo_component1. This has to be created before the index template as it is not optional:

response = client.cluster.put_component_template(
  name: 'logs-foo_component1',
  body: {
    template: {
      mappings: {
        properties: {
          "host.name": {
            type: 'keyword'
          }
        }
      }
    }
  }
)
puts response

PUT _component_template/logs-foo_component1
{
  "template": {
    "mappings": {
      "properties": {
        "host.name": {
          "type": "keyword"
        }
      }
    }
  }
}

Next, the index template will be created and it references two component templates:

  "composed_of": ["logs-foo_component1", "logs-foo_component2"]

Before, only the logs-foo_component1 compontent template was created, meaning the logs-foo_component2 is missing. Because of this the following entry was added to the config:

  "ignore_missing_component_templates": ["logs-foo_component2"],

During creation of the template, it will not validate that logs-foo_component2 exists:

response = client.indices.put_index_template(
  name: 'logs-foo',
  body: {
    index_patterns: [
      'logs-foo-*'
    ],
    data_stream: {},
    composed_of: [
      'logs-foo_component1',
      'logs-foo_component2'
    ],
    ignore_missing_component_templates: [
      'logs-foo_component2'
    ],
    priority: 500
  }
)
puts response

PUT _index_template/logs-foo
{
  "index_patterns": ["logs-foo-*"],
  "data_stream": { },
  "composed_of": ["logs-foo_component1", "logs-foo_component2"],
  "ignore_missing_component_templates": ["logs-foo_component2"],
  "priority": 500
}

The index template logs-foo was successfully created. A data stream can be created based on this template:

response = client.indices.create_data_stream(
  name: 'logs-foo-bar'
)
puts response

PUT _data_stream/logs-foo-bar

Looking at the mappings of the data stream, it will contain the host.name field.

At a later stage, the missing component template might be added:

response = client.cluster.put_component_template(
  name: 'logs-foo_component2',
  body: {
    template: {
      mappings: {
        properties: {
          "host.ip": {
            type: 'ip'
          }
        }
      }
    }
  }
)
puts response

PUT _component_template/logs-foo_component2
{
  "template": {
    "mappings": {
      "properties": {
        "host.ip": {
          "type": "ip"
        }
      }
    }
  }
}

This will not have an immediate effect on the data stream. The mapping host.ip will only show up in the data stream mappings when the data stream is rolled over automatically next time or a manual rollover is triggered:

response = client.indices.rollover(
  alias: 'logs-foo-bar'
)
puts response

POST logs-foo-bar/_rollover