nvim-lspconfig/lua/lspconfig/configs/dockerls.lua

-- !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
-- This config is DEPRECATED.
-- Use the configs in `lsp/` instead (requires Nvim 0.11).
--
-- ALL configs in `lua/lspconfig/configs/` will be DELETED.
-- They exist only to support Nvim 0.10 or older.
-- !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
local util = require 'lspconfig.util'

return {
  default_config = {
    cmd = { 'docker-langserver', '--stdio' },
    filetypes = { 'dockerfile' },
    root_dir = util.root_pattern 'Dockerfile',
    single_file_support = true,
  },
  docs = {
    description = [[
https://github.com/rcjsuen/dockerfile-language-server-nodejs

`docker-langserver` can be installed via `npm`:
```sh
npm install -g dockerfile-language-server-nodejs
```

Additional configuration can be applied in the following way:
```lua
require("lspconfig").dockerls.setup {
    settings = {
        docker = {
	    languageserver = {
	        formatter = {
		    ignoreMultilineInstructions = true,
		},
	    },
	}
    }
}
```
    ]],
  },
}