The gateway and recovery modules
Apart from our indices and the data indexed inside them, Elasticsearch needs to hold the metadata such as the type mappings and index-level settings. This information needs to be persisted somewhere so that it can be read during the cluster recovery. This is why Elasticsearch introduced the gateway module. You can think about it as a safe haven for your cluster data and metadata. Each time you start your cluster, all the required data is read from the gateway and when you make a change to your cluster, it is persisted using the gateway module.
The gateway
In order to set the type of gateway we want to use, we need to add the gateway.type property to the elasticsearch.yml configuration file and set it to a local value. Currently, Elasticsearch recommends that you use the local gateway type (gateway.type set to local), which is the default. There were additional gateway types in the past (such as the fs, hdfs, and s3), but they are deprecated and will be removed...
