mojolicious helper storing an elasticsearch connection

First of all, has and helper are not the same. has is a lazily built instance attribute. The only argument to an attribute constructor is the instance. For an app, it would look like:

package MyApp;has elasticsearch => sub {  my $app = shift;  Search::ElasticSearch->new($app->config->{es});};sub startup {  my $app = shift;  ...}

This instance is then persistent for the life of the application after first use. I'm not sure if S::ES has any reconnect-on-drop logic, so you might need to think about it a permanent object is really what you want.

In contrast a helper is just a method, available to the app, all controllers and all templates (in the latter case, as a function). The first argument to a helper is a controller instance, whether the current one or a new one, depending on context. Therefore you need to build your helper like:

has (elasticsearch => sub {  my ($c, $config) = @_;  $config ||= $c->app->config->{es};  Search::ElasticSearch->new($config);});

This mechanism will build the instance on demand and can accept pass-in arguments, perhaps for optional configuration override as I have shown in that example.

I hope this answers your questions.