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README.md
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README.md

Nodes

Notes and exercises while reading through Programming Elixir by Dave Thomas.

A node:

  • is a running Erlang VM
  • like a little OS
  • manages events, scheduling, memory, etc.
  • manages interprocess communication.

A node:

  • connects to other Nodes
  • provides services across connections just as it provides locally

Naming Nodes and Processes

$ iex --name scott@work.local
Erlang/OTP 19 [erts-8.1] [source] [64-bit] [smp:8:8] [async-threads:10] [hipe] [kernel-poll:false] [dtrace]

Interactive Elixir (1.3.4) - press Ctrl+C to exit (type h() ENTER for help)
iex(scott@work.local)1>

work:chapter16:Nodes smeade$ iex --sname node_one
Erlang/OTP 19 [erts-8.1] [source] [64-bit] [smp:8:8] [async-threads:10] [hipe] [kernel-poll:false] [dtrace]

Interactive Elixir (1.3.4) - press Ctrl+C to exit (type h() ENTER for help)
iex(node_one@work)1> Node.list
[]
iex(node_one@work)2> Node.list
[:node_two@work]
iex(node_one@work)3> func = fn -> IO.inspect Node.self end
#Function<20.52032458/0 in :erl_eval.expr/5>
iex(node_one@work)4> spawn(func)
:node_one@work
#PID<0.94.0>
iex(node_one@work)5> Node.spawn(:"node_one@work", func)
:node_one@work
#PID<0.96.0>

# Output appears here on node_one because
# the node_one hierarchy has the group leader
# which determines where IO.puts sends its output.
iex(node_one@work)6> Node.spawn(:"node_two@work", func)
:node_two@work
#PID<9267.98.0>

Exercise

iex(node_one@work)2> Node.spawn(:"node_one@work", fun)
README.md
#PID<0.90.0>
iex(node_one@work)3> Node.spawn(:"node_two@work", fun)
#PID<9415.91.0>
.ansible,.atom,.babel.json,.bash_history,.bash_profile..

Nodes, Cookies, and Security

  • nodes compare the remote node's cookie to its own cookie
  • when configuring a distributed Elixir system, you must create a cookie that all nodes use

Naming Your Processes

If you want to register a callback process on one node and an event- generating process on another, just give the callback PID to the generator. The callback on the other node can look up the generator by name, using the PID that comes back to send messages to it.

:global.register_name(:ticker, pid)
send :global.whereis_name(:ticker), { :register_client, client_pid }

Nodes Are the Basis of Distribution

We’ve seen how we can create and interlink a number of Erlang virtual machines, potentially communicating across a network. This is important, both to allow your application to scale and to increase reliability. -- Dave Thomas