Erlang in The Land of Lisp

As seen on PolyConf 2016, Clojure Remote 2016 and :clojureD 2016.

This talk is dedicated to lessons we’ve learned while designing, developing, and deploying to production our very first Erlang project. The audience of this talk will learn about differences between Clojure and Erlang, both at the linguistic level as well as, even more importantly, at the level of underlying virtual machines. I’m going to discuss how Erlang challenges our methods of building systems in Clojure. I’ll use our new Erlang-based project as a source of concrete differences.

Video: https://www.youtube.com/watch?v=qVMKIKJrUd8

Transcript

1. Erlang in the Land of Lisp
   with Jan Stępień @janstepien
   

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3. api.stylefruits.de
   ↑ ↓ ↑↑↑ ↓↓↓
   mobile client
   

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4. GET /v1/give-me-all-i-need-right-now
   Host: api.stylefruits.de
   Accept: applica on/truckload-of-json
   

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5. api.stylefruits.de
   ↑ ↓ ↑↑↑ ↓↓↓
   batching proxy
   ↑ ↓
   mobile client
   

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6. ↑↑↑ ↓↓↓
   HTTP client
   ↑↑↑ ↓↓↓
   JSON processing
   ↑ ↓
   HTTP server
   ↑ ↓
   

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7. ͜
   Rib
   Requests in Batches
   

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8. Erlang
   The syntax and the beauty beneath
   

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9. -module(qsort).
   -export([qsort/1]).
   qsort([]) -> [];
   qsort([Pivot|Rest]) ->
   qsort([Front || Front ++ [Pivot] ++
   qsort([Back || Back = Pivot]).
   en.wikipedia.org/wiki/Erlang (programming language)
   

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10. The Erlang VM
    where processes dwell
    p1 p2
    ↕
    p4 ↔ p3
    

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11. CPU CPU CPU CPU
    sched sched sched sched
    p0 p1 p2 p3 p4 p5 p6 p7 p8 p9
    

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12. Processes’ heaps are separated
    p0 p1 p2 p3 p4 p5
    

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16. Back to Rib
    Se ng the environment up
    

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17. $ rebar create-app appid=rib
    ==> rib (create-app)
    Writing src/rib.app.src
    Writing src/rib_app.erl
    Writing src/rib_sup.erl
    

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18. %% rebar.config
    {deps,
    [{jiffy, ".*",
    {git,
    "git://github.com/davisp/jiffy",
    {tag, "0.13.3"}}},
    {ejsonpath, ".*",
    {git,
    "git://github.com/rustyio/sync",
    "de3c42df58"}}]}.
    

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19. $ rebar sh
    ==> rib (shell)
    Erlang/OTP 18
    Eshell V7.0 (abort with ^G)
    1> sync:go().
    Starting Sync (Automatic Code Compiler / Reloader)
    Scanning source files...
    ok
    2>
    =INFO REPORT==== 7-Feb-2016::12:21:23 ===
    src/rib.erl:0: Recompiled.
    =INFO REPORT==== 7-Feb-2016::12:21:23 ===
    rib: Reloaded! (Beam changed.)
    

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20. Elli
    and callback modules
    

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21. -module(elli_minimal_callback).
    -behaviour(elli_handler).
    handle(Req, _Args) ->
    handle(Req#req.method, elli_request:path(Req), Req).
    handle('GET',[<>, <>], _Req) ->
    {200, [], <>};
    handle(_, _, _Req) ->
    {404, [], <>}.
    github.com/knu n/elli
    

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22. Let’s make it all concurrent
    

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23. pmap(Fun, List) ->
    Parent = self(),
    Workers =
    [spawn(fun() ->
    Parent ! {self(), Fun(X)}
    end)
    || X [receive
    {Worker, Value} -> Value
    end
    || Worker

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24. pmap(Fun, List) ->
    Parent = self(),
    Workers =
    [spawn_link(fun() ->
    Parent ! {self(), Fun(X)}
    end)
    || X [receive
    {Worker, Value} -> Value
    end
    || Worker

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25. pmap(Fun, List) ->
    Parent = self(),
    Workers =
    [spawn_link(fun() ->
    Parent ! {self(), Fun(X)}
    end)
    || X [receive
    {Worker, Value} -> Value
    after
    1000 -> error(timeout)
    end
    || Worker

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26. You shall not
    !
    

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27. OTP
    and generic behaviours in par cular
    

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28. Use case
    HTTP connec on killer
    

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29. -module(rib_conn_killer).
    -export([start_link/0]).
    start_link() ->
    {ok, spawn_link(fun go/0)}.
    go() ->
    {ok, Url} = application:get_env(rib, backend),
    Headers = [{"connection", "close"}],
    {ok, _} = httpc:request(get, {Url, Headers}),
    ok = timer:sleep(30000),
    go().
    

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30. -module(rib_conn_killer_sup).
    -behaviour(supervisor).
    -export([start_link/0, init/1]).
    start_link() ->
    supervisor:start_link({local, ?MODULE},
    ?MODULE,
    []).
    init([]) ->
    {ok, {{one_for_one, 5, 10},
    [{rib_conn_killer, ...}]}}.
    

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31. Use case
    Request limiter
    

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32. -module(rib_limiter).
    -behaviour(gen_server).
    start_link(Opts) ->
    gen_server:start_link(?MODULE, Opts, []).
    subtract(ServerRef, N) ->
    gen_server:cast(ServerRef, {subtract, N}).
    init({max, N}) ->
    {ok, N}.
    handle_cast({subtract, N}, State) ->
    NewState = State - N,
    case NewState >= 0 of
    true -> {noreply, NewState};
    false -> {stop, limit_exceeded, NewState}
    end.
    

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33. Deployment
    Lightweight Docker images
    

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34. Something completely different
    Happy path programming, le ng it crash
    

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35. On shoulders of giants
    Virtual machine, OTP
    

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36. Needs more research
    Polymorphism, editor integra on
    

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37. Can’t stand the syntax?
    LFE, Joxa, Elixir
    

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38. github.com/stylefruits/rib
    

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39. Erlang in the Land of Lisp
    with Jan Stępień @janstepien
    

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