Austin Clojure Meetup (8/12/2013) Updated for Dalls Clojure Meetup (8/22/2013) demo code: https://github.com/orb/pi-game

1. Norman Richards
orb@nostacktrace.comImmutant

2. Clojure Web Development
$ lein new compojure myapp
$ lein ring server
Congratulations, you now have a Clojure
web application listening on port 3000!

3. Immutant
What about?
? database
? messaging
? scheduling
? clustering
? production

4. Immutant
+ Based on JBoss AS 7
+ Makes use of Clojure standards (ring)
+ Production-ready stack out of the box

5. Setup
+ add immutant plugin to ~/.lein/profiles.clj
{:user
{:plugins [[lein-immutant "1.0.0"]]}

6. Setup
$ lein immutant install
Downloading http://repository-projectodd.forge.cloudbees.com/release/org/immutant/immutant-dist/1.0.0/immutant-dist-1.0.0-slim.zip
done!
Extracting /var/folders/jw/p379vgcn62q51q4_95xm1v6m0000gp/T/lein-immutant-8041099c-b2c5-4342-ac81-9e3986dfcbd2/immutant-dist-1.0.0-slim.zip
Extracted /Users/norman/.immutant/releases/immutant-1.0.0-slim
Linking /Users/norman/.immutant/current to /Users/norman/.immutant/releases/immutant-1.0.0-slim
The following versions of Immutant are installed to /Users/norman/.immutant
(* is currently active via /Users/norman/.immutant/current):
* 1.0.0 (type: slim)

7. Setup
$ lein immutant deploy
Deployed myapp to /Users/norman/.immutant/current/jboss/standalone/deployments/myapp.clj

8. Setup
$ lein immutant run
Starting Immutant: /Users/norman/.immutant/current/jboss/bin/standalone.sh
=========================================================================
JBoss Bootstrap Environment
JBOSS_HOME: /Users/norman/.immutant/current/jboss
JAVA: java
JAVA_OPTS: -server -XX:+UseCompressedOops -Xms64m -Xmx512m -XX:MaxPermSize=256m -Djava.net.preferIPv4Stack=true -
Djboss.modules.system.pkgs=org.jboss.byteman -Djava.awt.headless=true
=========================================================================
16:13:01,823 INFO [org.jboss.modules] (main) JBoss Modules version 1.2.0.CR1
16:13:02,294 INFO [org.jboss.msc] (main) JBoss MSC version 1.0.4.GA
16:13:02,344 INFO [org.jboss.as] (MSC service thread 1-6) JBAS015899: JBoss AS 7.2.x.slim.incremental.6 "Janus" starting
...
...
...
16:13:12,534 INFO [org.jboss.as] (Controller Boot Thread) JBAS015874: JBoss AS 7.2.x.slim.incremental.6 "Janus" started
in 10969ms - Started 128 of 175 services (46 services are passive or on-demand)

9. Setup
$ lein immutant run --clustered
...
...
16:17:44,573 INFO [org.jboss.as] (Controller Boot Thread) JBAS015874: JBoss AS 7.2.x.slim.incremental.6 "Janus" started
in 10170ms - Started 130 of 223 services (92 services are passive or on-demand)

10. Housekeeping
$ lein immutant undeploy
Undeployed /Users/norman/.immutant/releases/immutant-1.0.0-slim/jboss/standalone/deployments/myapp.clj

11. Housekeeping
$ lein immutant env
immutant-home: /Users/norman/.immutant/current
jboss-home: /Users/norman/.immutant/current/jboss

12. Housekeeping
$ lein immutant list
The following applications are deployed to /Users/norman/.immutant/current:
blue-app.clj (status: deployed)
red-app.clj (status: deployed)

13. Modules
+ immutant.web
+ immutant.xa
+ immutant.cache
+ immutant.messaging
+ immutant.jobs
+ immutant.daemons

14. immutant.web
(defproject somewebapp "0.1.0-SNAPSHOT"
;; ...
:plugins [[lein-ring "0.8.5"]]
:ring {:handler somewebapp.handler/app})
(defproject somewebapp "0.1.0-SNAPSHOT"
;; ...
:immutant {:nrepl-port 0
:context-path "/"})

15. immutant.web
(ns immutant.init
(:require [somewebapp.handler :as handler]
[immutant.web :as web]))
(web/start "/" handler/app)

16. immutant.web
/context-prefix /handler-path /app-path
From the deployment
From immutant init From your application

17. immutant.web
(def app
(-> app-routes
;; additional handlers
handler/site))
(def app
(let [store (immutant.web.session/servlet-store)]
(-> app-routes
;; additional handlers
(handler/site {:session {:store store}}))))

18. immutant.web
+ works with non-ring apps (eg. Pedestal)
+ control over virtual hosts and context paths
+ can dynamically start/stop endpoints
+ minimal changes to your code, framework agnostic

19. immutant.xa
(defonce my-datasource
(xa/datasource "mydb" {:adapter "postgres"
:host "33.33.33.50"
:username "db-user"
:password "db-password"
:database "my-awesome-db"}))
(def db-spec {:datasource my-datasource})

20. immutant.xa
(jdbc/with-connection db-spec
(jdbc/do-commands
"CREATE TABLE widgets (
name VARCHAR NOT NULL PRIMARY KEY,
count VARCHAR NOT NULL DEFAULT 0);"))
(jdbc/with-connection db-spec
(korma.core/select :widgets))
(def db-spec {:name "java:jboss/datasources/SomeExternalDS"})

21. immutant.xa
(defn new-widget [name number]
(let [widget {:name name :count number}]
(xa/transaction
(jdbc/with-connection db-spec
(korma/insert :widgets (korma/values widget)))
(msg/publish "/queue/widgets" widget))))

22. + integrates well with Clojure database things
+ XA transactions are tricky and hard to test
+ Most apps use many non-XA resources
+ database config can be external and shared
immutant.xa
+ All the immutant services are XA

23. immutant.cache
(def game-cache
(cache/create "game"
:persist true
:sync true))
(def job-cache
(cache/create "job-status"
:ttl 10
:idle 1
:units :minutes))

24. immutant.cache
(defn add-points [player points]
(let [current-score (get game-cache player 0)
new-score (+ current-score points)]
(cache/put game-cache player new-score)
new-score))

25. immutant.cache
+ Really easy to use
+ Interface isn’t very Clojure-like, needs abstraction
+ Should a data grid be deployed along side app?
+ Infinispan does much more than caching

26. immutant.messaging
(msg/start "/queue/orders")
(msg/start "/topic/new-widget")
(defn process-order [order]
(println "processing" order)
(msg/publish "/topic/new-widget" {:widget order}))
(defonce widgets (atom []))
(defn cache-widget [widget]
(swap! widgets #(conj % widget))
(println "I have" (count @widgets) "widgets"))
(msg/listen "/queue/orders" process-order)
(msg/listen "/topic/new-widget" cache-widget)

27. immutant.messaging
+ Priority, expiration, persistence, properties
+ Easy to toss around Clojure data structures
+ Pipelines are very cool
+ Topics and queues

28. immutant.jobs
(defonce heartbeat (atom nil))
(defn send-heartbeat []
(riemann/send-event {:service "heartbeat" :state "ok" :metric 1}))
(defn heartbeat-thread [every-n-sec]
(while true
(send-heartbeat)
(Thread/sleep (* 1000 every-n-sec))))
(defn start-heartbeat []
(swap! heartbeat
(fn [heartbeat]
(or heartbeat
(doto (Thread. #(heartbeat-thread 10))
.start)))))
(defn stop-heartbeat []
(swap! heartbeat
(fn [heartbeat] (when heartbeat (.stop heartbeat)))))

29. immutant.jobs
(defn send-heartbeat []
(riemann/send-event {:service "heartbeat" :state "ok" :metric 1}))
(defn start-heartbeat []
(jobs/schedule :heartbeat
send-heartbeat
:every 10000))
(defn stop-heartbeat []
(jobs/unschedule :heartbeat))

30. + Also supports CRON-like scheduling syntax
+ Can be used for ad-hoc jobs
+ Not easy to see what jobs are scheduled/running
+ Jobs can be on all nodes or just one
immutant.jobs

31. immutant.daemons
(defonce listener (atom nil))
(defn start-listener []
(swap! listener
(fn [listener]
(msg/listen "/queue/guesses" play/handle-guess))))
(defn stop-listener []
(swap! listener
(fn [listener]
(when listener
(msg/unlisten listener)))))
(daemon/daemonize "guess-listener"
start-listener
stop-listener
:singleton true)

32. immutant.daemons
+ Can be long running
+ Singleton processes can be reliably setup
+ Manage application-specific services

33. The PI Game
π
https://github.com/orb/pi-game

34. PI Game Demo
+ EDN api to get state and send actions
+ Game state saved in persistent cache
+ Clojurescript front end, Clojure back end
+
+
+ Player actions are sent to guess queue
Singleton daemon creates one listener per cluster
Demo uses two immutant nodes with nginx in front

35. But...
• Works out of the box
• It’s good Clojure - not “Clojure 2
Enterprise Edition”
• Best solution for multiple applications
• Best solution when you want to work
with Java or Ruby apps
• JBoss is production tested
• Responsive dev team
• Are these the services you
would have chosen?
• It’s one big blob, not lots of
composable blocks
• Does it fit your application
architecture?
• Does it fit your ops strategy?
Yes

36. • App was ring/jetty - using our own custom startup
• Wanted to split our APIs out and modularize app instead of
deploying as a monolithic app
• Wanted to be able to support rolling updates across nodes
• Liked the idea of being able to bring mature clustering, caching
and messaging into the app almost for free
Immutant at Threatgrid

37. • Transition to Immutant was very fast and required only minor
changes to our customized startup code
• We ran into a few small issues, but the Immutant dev team had
almost immediate fixes/workarounds.
• Transitional codebase still supports running outside Immutant,
so we haven’t been able to leverage some features
• Ops team strongly prefers individual services that can be
managed independently - Immutant is one big ball
• Our web nodes and data nodes scale separately - Immutant
seems to prefer a more homogenous deployment
• Immutant a la carte would really hit a sweet spot
And.... we’re still deciding