Elsaticsearch reindex zero downtime

Photo by Austin Neill on Unsplash

I think this is the most straightforward strategy and super easy way

let’s say…
petshop-index = currently index that we use
petshop-index_v2 = new index

STEP1 :

Add the new aliases to petshop-index as assume naming it to petshop-index_latest ( The reason why I naming it like that because if we want to reindex in the next time we don't need to re-point an application to use new aliases just keep it latest :) )

POST _aliases
{
  "actions": [
      { 
        "add": {
          "alias": "petshop-index_latest",
          "index": "petshop-index"
        }
      }
    ]
}

STEP2 :

Create a new index that you want to reindex (change the mapping, field type, etc)

PUT /petshop-index_v2
{
  "settings": {
    "index": {
      "number_of_shards": 10,
      "sort.field" : "bill_date",
      "sort.order": "desc"
    }
  },
  "mappings": {
     ...
  }
}

STEP3 :

After you already have a new index it’s time to move all incoming traffic to the new index by changing aliases. Formally we point
[ petshop-index_latest ->petshop-index ]
but now we have to change it to
[ petshop-index_latest ->petshop-index_v2 ]
So, when you finished doing that you can count a document and you’ll see all traffic come to petshop-index_v2 instead of petshop-index

POST _aliases
{
  "actions": [
      { 
        "remove": {
          "alias": "petshop-index_latest",
          "index": "petshop-index"
        }
      },
      { 
        "add": {
          "alias": "petshop-index_latest",
          "index": "petshop-index_v2"
        }
      }
    ]
}

STEP4 :

Reindex your own data move from petshop-index to petshop-index_v2

POST _reindex?wait_for_completion=false
{
  "source": {
    "index": "petshop-index"
  },
  "dest": {
    "index": "petshop-index_v2"
  }
}

Note: use wait_for_completion for running reindex task in the background process. It gonna return task id so, you can check it out how about your process by using TaskAPI

GET /_tasks/O0bQQ8VYQ0yiWNrDaTmrtA:20830445

Happy searching….

Ref:

Reindex API | Elasticsearch Reference [7.6] | Elastic

Task management API | Elasticsearch Reference [7.6] | Elastic

Update index alias API | Elasticsearch Reference [7.6] | Elastic

Good cover image by:
Photo by Austin Neill on Unsplash