How to set a timeout on a Hystrix command in Clojure? - clojure

Question

I'm learning about Hystrix and Clojure and don't understand how to (properly) set a timeout on a Hystrix command in Clojure.
I searched StackOverflow and the web more generally. I looked at Hystrix's Clojure wrapper source code (https://github.com/Netflix/Hystrix/blob/master/hystrix-contrib/hystrix-clj/src/main/clojure/com/netflix/hystrix/core.clj). There is a init-fn function parameter that looked promising, but the comments seem to suggest that this won't be a sustainable solution. But would this be a simple start?
I have a ridiculously simple Hystrix command running in Clojure and would appreciate help in extending this to set, say, a 200ms timeout:
(ns hystrix-timeout.core
(:require [clojure.string :as str])
(:require [com.netflix.hystrix.core :as hystrix])
(:gen-class))
(defn my-primary [a]
(if (= a true) (throw (Exception. "Primary failed")) (str "primary: " a)))
(defn my-fallback [a]
(str "fallback: " a))
(hystrix/defcommand my-command
{:hystrix/fallback-fn my-fallback}
[a]
(my-primary a))
(defn -main
"Executes a simple Hystrix command. Will use a timeout when I know how to do this in Clojure."
[& args]
(println (my-command false))
(println (my-command true))
(System/exit 0) ; Exit explicitly as Hystrix threads are still running.
)
I've put my lein project up at https://github.com/oliverbaier/learning/tree/master/hystrix-timeout in case this makes answering easier.
Thanks a lot,
Oliver

Answer 1

The simplest route is to just use System properties. You can set either a global default:
(System/setProperty "hystrix.command.default.execution.isolation.thread.timeoutInMilliseconds" "200")
or a command specific value:
(System/setProperty "hystrix.command.my-command.execution.isolation.thread.timeoutInMilliseconds" "200")
You can perform this in your -main method. If you are running a real web-app sans -main, you can add a ring init in project.clj :ring {:handler your-handler :init your-config-method} your-config-method will be invoked on startup.