whitfin/local-cluster

Easy local cluster creation for Elixir to aid in unit testing

local-cluster's Issues

Getting 'undefined function' error on simple test

I wrote a simplified version of a test based on the documentation, over here: https://github.com/whitfin/local-cluster#usage

However, when I run the test it fails (message not received), and I see the following error in stdout:

$ mix test
.
10:03:57.708 [error] Process #PID<20934.220.0> on node :"[email protected]" raised an exception
** (UndefinedFunctionError) undefined function
    #Function<0.60679234/0 in ChatTest."test test node things"/1>()

10:03:57.708 [error] Process #PID<0.220.0> on node :"[email protected]" raised an exception
** (UndefinedFunctionError) undefined function
    #Function<0.60679234/0 in ChatTest>()


  1) test test node things (ChatTest)
     test/chat_test.exs:5
     Assertion failed, no matching message after 100ms
     The process mailbox is empty.
     code: assert_receive :a_message_from_the_node
     stacktrace:
       test/chat_test.exs:14: (test)


Finished in 3.1 seconds (0.00s async, 3.1s sync)
1 doctest, 1 test, 1 failure

Randomized with seed 660329

My test looks as follows:

defmodule ChatTest do
  use ExUnit.Case
  doctest Chat

  test "test node things" do
    [n1, _n2, _n3] = LocalCluster.start_nodes("my-cluster", 3)

    caller = self()

    _n1_pid = Node.spawn(n1, fn ->
      send(caller, :a_message_from_the_node)
    end)

    assert_receive :a_message_from_the_node
  end
end

My test_helper.exs:

# start the current node as a manager
:ok = LocalCluster.start()

# start your application tree manually
Application.ensure_all_started(:my_app)

# run all tests!
ExUnit.start()

My mix.exs:

defmodule Chat.MixProject do
  use Mix.Project

  def project do
    [
      app: :chat,
      version: "0.1.0",
      elixir: "~> 1.14",
      start_permanent: Mix.env() == :prod,
      deps: deps(),
      aliases: [
        test: "test --no-start"
      ]
    ]
  end

  def application do
    [
      extra_applications: [:logger],
      mod: {Chat.Application, []}
    ]
  end

  defp deps do
    [
      {:local_cluster, "~> 1.2", only: [:test]}
    ]
  end
end

My elixir version:

$ elixir --version
Erlang/OTP 25 [erts-13.0.4] [source] [64-bit] [smp:10:10] [ds:10:10:10] [async-threads:1] [jit]

Elixir 1.14.0 (compiled with Erlang/OTP 25)

Anything obvious that I'm doing wrong?
I get the same behavior when I use receive do ... instead of assert_receive
When I delete the assert_receive line, I don't get the 'undefined function` error anymore.

Error when running `LocalCluster.start/0`

When running LocalCluster.start/0 I get the following error:

{:error, 
  {{:shutdown, {:failed_to_start_child, :net_kernel, {:EXIT, :nodistribution}}},  
   {:child, :undefined, :net_sup_dynamic,   
    {:erl_distribution, :start_link, [[:"[email protected]"], false]},   
    :permanent, 1000, :supervisor, [:erl_distribution]}}}

I followed the getting started guide, other then that I have a pretty simple phoenix app with some other deps.

This is my Elixir and Erlang/OTP version:

Erlang/OTP 21 [erts-10.3] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [hipe] [dtrace]
Elixir 1.8.1 (compiled with Erlang/OTP 21)

Any clue?

Crashes with certain cookies

Some systems generate cookies that have special characters in them, this trips the shell when supplying that cookie with the -setcookie option.

For example, I have the cookie 0mwHxf/~5h{?|pm<ST1PCtean_Be~bT9386.5O9!RL2s5=[YkPLCew%^@[A&CO^x, and shell outputs these errors:

sh: ST1PCtean_Be~bT9386.5O9!RL2s5=[YkPLCew%^@[A: No such file or directory
sh: CO^x: command not found

This is easily fixed by wrapping the cookie with quotes.

How to start a supervisor in the slave nodes?

I am working on a Spawnfest idea and I am using LocalCluster to test the distribution. If I start my supervision tree implicitly (with the :mod key), then Application.ensure_started works and LocalCluster's doc document as much (started applications are replicated to slave nodes).

But how does it work if I don't want to start my app up implicitly? Instead of starting it implicitly, I am requiring users to put it in their supervision tree. In my test, I can manually call start_link to start it which is pretty neat, but when LocalCluster is involved, I am not able to get these supervision tree started there.

I tried to do a :rpc.call(node1, MySupervisor, :start_link, []) but that doesn't work either, is it not possible?

Can we start nodes with test env (MIX_ENV=test)?

Is there a way to start the nodes with test env (MIX_ENV=test)?
I'm using Swarm as a dependency, and by default it logs a lot of data when running in dev mode (info and debug).
While using Local Cluster in a test, I can see all the logs Swarm produces from all nodes on the test cluster as they're running with dev environment.

Is there a way to prevent all these logs to appear during tests but keep them for dev?

Update the readme to show ExUnit.start can run before LocalCluster.start ?

I was following the readme to the letter recently by running LocalCluster.start before my ExUnit.start in the test_helper (Phoenix) but ... strangely enough it turns out you can run the LocalCluster.start in a single setup for just 1 test meaning the ExUnit.start can remain in the test_helper as you would see in any default application layout.

Any reason we can't update the readme to reflect this^ world view?

note: working example app w/ my results to prove its fine running after ExUnit.start

toranb/elixir-budget@b657a18

umbrella apps config

I see that application configs are passed to spawned nodes here

local-cluster/lib/local_cluster.ex

Line 70 in f86e6f0

rpc.(Application, :put_env, [ app_name, key, val ])

And looks like it works, but sometimes in my umbrella project some applications are terminating because of missing configs. I have 2 suggestions

• some umbrella app somehow is getting started before this line is executed

  local-cluster/lib/local_cluster.ex

  Line 70 in f86e6f0

  rpc.(Application, :put_env, [ app_name, key, val ])

• some umbrella app is not loaded (and loading later with missing config)

  local-cluster/lib/local_cluster.ex

  Line 68 in f86e6f0

  for { app_name, _, _ } <- Application.loaded_applications() do

is it possible?

Feature Request: Simulating slow or unstable connections

I'd like to use this library not inside unit-tests, but inside some integration tests that ensure that the core functionality of our distributed application (https://planga.io) keeps functioning within expected bounds, even if the connection between nodes is slow, or if from time to time requests are being dropped.

What do you think? 🙂

Can't load libcluster configuration

Hi, I'm using https://github.com/bitwalker/libcluster to setup, well, the cluster 😄
But, for some reason, creating nodes from test via LocalCluster.start_nodes("my_cluster", 2) doesn't pick up libcluster configuration.

In config/config.exs I have:

config :my_app, MyAppWeb.Endpoint,
  ...

config :libcluster,
  topologies: [
    local: [
      strategy: Cluster.Strategy.Gossip,
      connect: {:net_kernel, :connect_node, []},
      disconnect: {:erlang, :disconnect_node, []},
      list_nodes: {:erlang, :nodes, [:connected]}
    ]
  ]

And in application.ex I use topologies = Application.fetch_env!(:libcluster, :topologies) to fetch that configuration and supply it to libcluster. However, :libcluster configuration is empty for nodes created via LocalCluster. At the same time, it is properly picked up when project is started in dev/prod mode and manager node started with tests also picks it up correctly.

In test helper I have:

:ok = LocalCluster.start()
Application.ensure_all_started(:my_app)
ExUnit.start()

Note that if I change the configuration to config :my_app instead of config :libcluster, it all works correctly (configuration is picked up). So there is a workaround, but I'd still like to be able to set the config key properly. Funny thing is, e.g. config :logger is correctly picked up.

Starting local cluster with the main node as a hidden node?

The title here is probably more of a potential solution then the underlying problem.

In a lot of my tests I need to ensure that nodes discover and connect to each other. But when local cluster the primary node connects to the other nodes and creates a full mesh between all of the existing nodes. I'm not even sure if what I want to do is possible but I'm wondering if there's a programatic way to start the main node as a hidden node or something similar so that the cluster behaves as though the main node isn't truly a part of the cluster. I know that you can pass an erl flag to set a node as hidden but I'm not sure if you can do that once the node is already booted.

I might be going in a totally wrong direction here (and if so please tell me so) but I wanted to get your thoughts on it.

Some clarifications

Hello!

Tried this library and got permanent :not_alive error on LocalCluster.start_nodes
Also your library test returned this

00:02:37.767 [info]  Protocol 'inet_tcp': register/listen error: econnrefused                                                                                                                                                   
                                                                                                                                                                                                                                
** (MatchError) no match of right hand side value: {:error, {{:shutdown, {:failed_to_start_child, :net_kernel, {:EXIT, :nodistribution}}}, {:child, :undefined, :net_sup_dynamic, {:erl_distribution, :start_link, [[:"manager@1
27.0.0.1"], false]}, :permanent, 1000, :supervisor, [:erl_distribution]}}}                                                                                                                                                      
    test/test_helper.exs:2: (file)                                                                                                                                                                                              
    (elixir) lib/code.ex:813: Code.require_file/2                                                                                                                                                                               
    (elixir) lib/enum.ex:783: Enum."-each/2-lists^foreach/1-0-"/2    

I am not sure - may be this issue is trivial and self obvious for true erlang developers, but for noobs like me it was kind of pain.

Finally I got the reason - there must be epmd daemon running.

So may be reflect this requirements in documentation? It seems mandatory condition so looks logical for me to write couple of lines about it.