Breaking changes in 6.1

This section discusses the changes that you need to be aware of when migrating your application to Elasticsearch 6.1.

Bootstrap checks now apply to link-local addresses

Previously when Elasticsearch was bound to localhost, Elasticsearch would bind to any address on the loopback device. This included link-local addresses on the loopback device such as fe80::1%lo0 on macOS. Starting in 6.1.2, Elasticsearch will now only bind to loopback addresses on the loopback device. Because of the previous behavior, Elasticsearch would skip the bootstrap checks if bound to a link-local address. Now that Elasticsearch no longer binds to such addresses when binding to localhost, the bootstrap checks now apply to link-local addresses.