Riemann example how to check whether a host is in maintenance mode. And Ruby code to set/unset maintenance mode.

riemann-maintenance-mode.rb

vagrant@precise64:~$ irb
1.9.3-p484 :002 > require "riemann"
 => true
# Activate maintenance-mode:
1.9.3-p484 :010 > Riemann::Client.new << {service: "maintenance-mode", host: "precise64", state: "active", ttl: Float::INFINITY}
 => nil
# Deactivate maintenance-mode:
1.9.3-p484 :011 > Riemann::Client.new << {service: "maintenance-mode", host: "precise64", state: nil, ttl: Float::INFINITY}
 => nil

riemann.config

; vim: filetype=clojure
(logging/init :file "/var/log/riemann.log")
; everything is available on the public interface

; probably not the best idea for a production system
(tcp-server :host "0.0.0.0")
(udp-server :host "0.0.0.0")
(ws-server :host "0.0.0.0")
(repl-server :host "0.0.0.0")
(periodically-expire 10)

; (maintenance-mode? "host-name") is true when the index has an entry 
; for the service "maintenance-mode" with the state "active" for the host "host-name"
(defn maintenance-mode? [host]
  "Is this host currently in maintenance mode?"
  ; Take an expression representing a query for maintenance mode
  (->> (list 'and (list '= 'host host)
                  '(= service "maintenance-mode"))
       ; Search the current Riemann core's index for any matching events
       (riemann.index/search (:index @core))
       ; Take the first match
       first
       ; Find its state
       :state
       ; Is it the string "active"?
       (= "active")))

(let [client (tcp-client)
  ; Keep events for 5 minutes by default
  index (default :ttl 300 (update-index (index)))]
  (streams
    ; Print all streams when the host "precise64" is not in maintenance mode 
    ; (this is just a demo)
    (where (not (maintenance-mode? "precise64"))
        #(info "the host precise64 is not in maintnance mode, OK?" %))
    index
))