indexes.yml

# Indexes
mongodb_indexes:
  catalog: [
    "db.serviceMetadata.createIndex({service: 1, objectId: 1},{background: true})",
    "db.program.createIndex({title:1},{background : true})" ]
  guid: [
    "db.guids.createIndex({type:1},{background:true})",
    "db.guids.createIndex({'data.peopleInfo.type':1,'data.peopleInfo.firstname':1},{background:true, sparse:true})" ]

task.yml

tasks:
  - name: Setup mongodb indexes
    debug: msg="Key is {{ item.key }} with items {{ item.value }}"
    with_dict: mongodb_indexes

# Indexes
mongodb_indexes:
  catalog: 
    sublist: 
      - "db.serviceMetadata.createIndex({service: 1, objectId: 1},{background: true})"
      - "db.program.createIndex({title:1},{background : true})" 
  guid: 
    sublist:
      - "db.guids.createIndex({type:1},{background:true})"
      - "db.guids.createIndex({'data.peopleInfo.type':1,'data.peopleInfo.firstname':1},{background:true, sparse:true})"

- dosomething: name={{ item.0 }} listitem={{ item.1 }}
  with_subelements:
    - mongodb_indexes
    - sublist

hmm, unfortunately the above didn't work, the item.0 only returned {}. instead, it needed this format

- hosts: foo
  vars:
    mongodb_indexes:
      - name: catalog
        sublist:
          - "db.serviceMetadata.createIndex({service: 1, objectId: 1},{background: true})"
          - "db.program.createIndex({title:1},{background : true})"
      - name: guid
        sublist:
          - "db.guids.createIndex({type:1},{background:true})"
          - "db.guids.createIndex({'data.peopleInfo.type':1,'data.peopleInfo.firstname':1},{background:true, sparse:true})"
  tasks:
     - debug: msg="name is {{ item.0.name }}, listitem is {{ item.1 }}"
       with_subelements:
         - mongodb_indexes
         - sublist

which is basically like a with_together, except the second list is nested. Not what i was expecting, and it's annoying it didn't allow just the key.