Preheat a grill to a high temperature in the indirect heat zone, about 500 degrees F (260 degrees C). The grill needs to be ready to go so the onion rings can be battered and cooked with as little rest time in the process as possible.
Beer Batter
In a bowl combine the flour, cornstarch, and salt.
Slowly pour in the pale ale while whisking continually to keep as smooth as possible. Stop adding the beer when it gets to the desired thickness.
Add the Sriracha sauce to your desired taste or heat level. If you want it to have a red color but not add too much Sriracha sauce you can add a small amount of sweet paprika.
Onion Rings
Thickly slice the onions then dip them in the batter.
Sprinkle the onion rings lightly with the all-purpose BBQ rub.
Place the battered onion rings on the preheated grill as soon as practical and cook for up to 20 minutes, or until the batter is crisp and the onions are soft. Serve immediately, otherwise, the batter will soften.