Chef resource to register gitlab runner automatically We would like to automate installation of gitlab runner using chef.  we are  successful with it. Now, the Issue is regarding registering gitlab runner with chef resource.
we have gone through chef resource. and official cookbook https://gitlab.com/chef-platform/gitlab-ci-runner but looks a bit complicated for us. we wonder if we have any pre-built chef resources to register gitlab runner. if yes, can we know how we can register with a example resource.
Additionally, I have tried looking at resource https://github.com/TYPO3-cookbooks/site-gitlabcirunnertypo3org/blob/master/recipes/default.rb  

name = "#{node['fqdn']}-docker"
  gitlab_ci_runner name do
      options(
        registration_token: registration_token,
        url: node['site-gitlabcirunnertypo3org']['gitlab_url'],
        executor: 'docker',
        :'docker-image' =&gt; 'docker:1',
        :'tag-list' =&gt; ['docker']
      )
end


But I dont understand how it is registering the runner. Thanks for help!
Your second link just use the official cookbook. This official cookbook still uses the LWRP syntax, so you need to check in the provider directory for the resource action code -- which for register is basically just two execute commands (extract from the file linked above):

converge_by("Register runner #{new_resource.description}") do
  execute "#{env} gitlab-runner register --non-interactive #{options}"
  # giving time to gitlab-ci to manage the request
  execute "sleep #{new_resource.sleep}"
end


So mostly, your exemple ends up calling the gitlab-runner register command with the options defined in the options hash (with a little transformation of the hash into command parameters).

There's no 'core' chef resource to register gitlab runners out of using an execute resource to run the command.

A basic example of this resource is present in the cookbook Readme:

gitlab_ci_runner 'my runner' do
  options({
    registration_token: '1234567890',
    url: 'http://gitlab-ci.myinstance'
  })
end