Modify Elasticsearch mappings and settings without downtime

Here is a 3 steps procedure to modify mappings and settings on an existing index without downtime. No need to manually re-import everything.

Step 1: Create a new index

Let’s say the original index name is things. Create a new index with another name with the new settings and mappings properties:

PUT things2
{
  "mappings": {
    "_doc": {
      "properties": {
        "foo": {
          "type": "text",
          "analyzer": "french"
        }
      }
    }
  }
}

Step 2: Re-index from old index to new index

Then you need to copy the docs from things to things2:

POST _reindex
{
  "source": {
    "index": "things"
  },
  "dest": {
    "index": "things2"
  }
}

Step 3: Create an alias for new index

Finally, you can drop the old index and create an alias for the new one with the same name as the previous one.

POST _aliases
{
  "actions" : [
    { "add":  { "index": "things2", "alias": "things" } },
    { "remove_index": { "index": "things" } }  
  ]
}

Voilà! You can use things as usual with the new settings and mappings. 🎉