Alistar Runes explained
There's one set of runes for Alistar on patch
11.19
that is the clear favorite for LoL players and pros alike. The best Alistar Runes on the position 
Support are Resolve as the primary path and
Inspiration as the secondary path with a pick rate of 82%. Besides runes you should take a look on Alistar Build and if you are interested in pro matches take a look at Alistar Probuilds. If you want to discuss
Alistar then you should visit the champion subreddit.
Primary path on Alistar
Resolve empowers the survivability of Alistar and increases the tankiness. Most of high elo players – and our LoL pros in the the major regions – have agreed that
Aftershock is the best keystone rune to run on
Alistar. This keystone rune bulks you up, increasing both armour and magic resistance, once you immobilized a champion.
Aftershock synergises both with the sheer amount of crowd control Alistar possesses and the need to be tanky as soon as you engage. This is usually followed up by taking
Font of Life,
Bone Plating and
Unflinching.
Font of Life provides your teammates with more sustain by healing them whenever they attack a champion whose movement you've recently impaired.
Bone Plating make Alistar overall tankier, by decreasing the amount of poke damage in the early game.
Unflinching inceases Alistar tenacity based on your missing health.
Secondary path on Alistar
When it comes to your secondary path, most
Alistar players prefer to go with
Inspiration.
Inspiration opens creative opportunities on Alistar troughout the match. On the
Inspiration path, the best runes for Alistar are
Hextech Flashtraption and
Cosmic Insight.
Having an extra way to decrease the distance with the
Hextech Flashtraption will make an engage much easier to pull off.
Cosmic Insight grants summoner spell and item haste.