Breaking changes in 5.5

Previous versions of Elasticsearch would skip hidden files and directories when scanning the plugins folder. This allows broken plugin installs to remain undetected so this leniency has been removed.

Elasticsearch attempts to set the kernel parameter vm.max_map_count during installation. In some environments this can fail. Previous versions of Elasticsearch accepted a flag ES_SKIP_SET_KERNEL_PARAMTERS to skip this writing. Starting in Elasticsearch 5.5.0, this flag has been removed and instead the same functionality can be achieved by masking the systemd-sysctl service.

The RPM and Debian packages now set the setgid flag on /etc/elasticsearch so that any files and subdirectories created under /etc/elasticsearch have the same ownership as /etc/elasticsearch (root:elasticsearch). This is used to ensure that files and subdirectories created under /etc/elasticsearch (e.g., a keystore) are readable by the elasticsearch user.

Previous versions of Elasticsearch did not return a 404 in all cases when a requested alias or a requested type did not exist on the get alias or get mapping APIs, respectively. Starting in Elasticsearch 5.5.0, these APIs consistently return a 404 in any case when an alias or type is requested that does not exist.

The has_child, has_parent and parent_id queries have moved to parent-join module. Also the children aggregation has been moved to the parent-join module. The parent-join module should be loaded when using the transport client. Alternatively use the PreBuiltTransportClient client, which load the module automatically.