## First, add a couple of pipelines that set a field to a boolean:
PUT /_ingest/pipeline/foo-pipeline?pretty
{
  "processors": [
    {
      "set": {
        "field": "foo",
        "value": true
      }
    }
  ]
}

PUT /_ingest/pipeline/bar-pipeline?pretty
{
  "processors": [
    {
      "set": {
        "field": "bar",
        "value": true
      }
    }
  ]
}

## Now, create two component templates. One provides a mapping enforces that the only field is "foo"
## and that field is a keyword. The other provides a setting that makes "foo-pipeline" the default pipeline.
## Remember that the "foo-pipeline" sets the "foo" field to a boolean, so using both of these templates
## together would cause a validation exception. These could be in the same template, but are provided
## separately just so that later we can show how multiple templates can be overridden.
PUT _component_template/mappings_template
{
  "template": {
    "mappings": {
      "dynamic": "strict",
      "properties": {
        "foo": {
          "type": "keyword"
        }
      }
    }
  }
}

PUT _component_template/settings_template
{
  "template": {
    "settings": {
      "index": {
        "default_pipeline": "foo-pipeline"
      }
    }
  }
}

## Here we create an index template  pulling in both of the component templates above
PUT _index_template/template_1
{
  "index_patterns": ["foo*"],
  "composed_of": ["mappings_template", "settings_template"]
}

## We can index a document here to create the index, or not. Either way the simulate call ought to work the same
POST foo-1/_doc
{
  "foo": "FOO"
}

## This will not blow up with validation exceptions because the substitute "mappings_template" sets
## dynamic to true so that the introduction of the "bar" field doesn't cause problems.
## And the bar-pipeline is executed rather than the foo-pipeline because of the substitute 
## "settings_template", so the value of "foo" does not get set to an invalid type.
POST _ingest/_simulate?pretty&index=foo-1
{
  "docs": [
    {
      "_id": "asdf",
      "_source": {
        "foo": "foo",
        "bar": "bar"
      }
    }
  ],
  "template_substitutions": {
    "mappings_template": {
      "mappings": {
        "dynamic": "strict",
        "properties": {
          "foo": {
            "type": "keyword"
          },
          "bar": {
            "type": "boolean"
          }
        }
      }
    },
    "settings_template": {
      "settings": {
        "index": {
          "default_pipeline": "bar-pipeline"
        }
      }
    }
  }
}