elasticsearch_create_alias.rb

req_body_for_patient_a = {
  routing: 'PatientA',
  filter: {
    term: { patient_name: 'PatientA' }
  }
}

req_body_for_patient_b = {
  routing: 'PatientB',
  filter: {
    term: { patient_name: 'PatientB' }
  }
}

raw_put 'patients/_alias/PatientA', req_body_for_patient_a
raw_put 'patients/_alias/PatientB', req_body_for_patient_b

client.indices.exists_alias? name: 'PatientA' # => true
client.indices.exists_alias? name: 'PatientB' # => true