Reindex to upgrade

Elasticsearch is able to use indices created in the previous major version only. For instance, Elasticsearch 5.x can use indices created in Elasticsearch 2.x, but not those created in Elasticsearch 1.x or before.

Elasticsearch 5.x nodes will fail to start in the presence of too old indices.

If you are running an Elasticsearch 2.x cluster which contains indices that were created before 2.x, you will either need to delete those old indices or to reindex them before upgrading to 5.x. See Reindex in place.

If you are running an Elasticsearch 1.x cluster, you have two options:

Reindex in place

The easiest way to reindex old (1.x) indices in place is to use the Elasticsearch Migration Plugin. You will need to upgrade to Elasticsearch 2.3.x or 2.4.x first.

The reindex utility provided in the migration plugin does the following:

  • Creates a new index with the Elasticsearch version appended to the old index name (e.g. my_index-2.4.1), copying the mappings and settings from the old index. Refresh is disabled on the new index and the number of replicas is set to 0 for efficient reindexing.
  • Sets the old index to read only to ensure that no data is written to the old index.
  • Reindexes all documents from the old index to the new index.
  • Resets the refresh_interval and number_of_replicas to the values used in the old index, and waits for the index to become green.
  • Adds any aliases that existed on the old index to the new index.
  • Deletes the old index.
  • Adds an alias to the new index with the old index name, e.g. alias my_index points to index my_index-2.4.1.

At the end of this process, you will have a new 2.x index which can be used by an Elasticsearch 5.x cluster.

Upgrading with reindex-from-remote

If you are running a 1.x cluster and would like to migrate directly to 5.x without first migrating to 2.x, you can do so using reindex-from-remote.

Elasticsearch includes backwards compatibility code that allows indices from the previous major version to be upgraded to the current major version. By moving directly from Elasticsearch 1.x to 5.x, you will have to solve any backwards compatibility issues yourself.

You will need to set up a 5.x cluster alongside your existing 1.x cluster. The 5.x cluster needs to have access to the REST API of the 1.x cluster.

For each 1.x index that you want to transfer to the 5.x cluster, you will need to:

  • Create a new index in 5.x with the appropriate mappings and settings. Set the refresh_interval to -1 and set number_of_replicas to 0 for faster reindexing.
  • Use reindex-from-remote to pull documents from the 1.x index into the new 5.x index.
  • If you run the reindex job in the background (with wait_for_completion set to false), the reindex request will return a task_id which can be used to monitor progress of the reindex job in the task API: GET _tasks/TASK_ID.
  • Once reindex has completed, set the refresh_interval and number_of_replicas to the desired values (the defaults are 30s and 1 respectively).
  • Once the new index has finished replication, you can delete the old index.

The 5.x cluster can start out small, and you can gradually move nodes from the 1.x cluster to the 5.x cluster as you migrate indices across.