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Distributest

Distributed/Concurrent Ruby test runner written in Erlang.

NOTE

I haven't worked on this much lately. I originally planned on rewriting using OTP and fixing some of the bugs. However, I have come to realize if your project needs this, it has already failed. There are very few applications that truly have slow running proper test suites. If you find that yours is slow your doing it wrong.

If you have a test suite that runs in 10 seconds but you want it to be faster, there are better choices than a fully distributed system such as this.

Description

Distributest allows you to run your tests across multiple cores on multiple nodes. It is designed to not interfere with anyone that is using the nodes the tests are distributed to. Devs on the other nodes can also run distributed tests for the same project at the same time without issue.

Installation

You need Erlang installed on every box you intend to distribute to/from. Tested heavily with R13B04

Clone this project to any folder

Go into folder and run:

  • rake compile

  • rake install_gem

  • sudo rake install

This needs to be done on every node your distributing to including your local box.

This will install the app into /usr/local/distributest and make symlinks for the scripts used to start the Erlang vms.

Run rake -T for more options although they are limited at the moment.

Configuration

Inside the project there is a folder named move_following_folders. Copy or move the distributest folder in to_etc to /etc on your box. The other folders are an example of how you can override the systems configurations per project. I haven't had a need for this and it may or may not do want you want. Read the comments in the files if you need to override the settings from /etc/distributest with ones from your Ruby project

Edit set_hostname.sh and replace the comment with the fully qualified name of the box it's installed on. This is needed by most boxes as I am expecting fully qualified names to be used to communicate between the erlang VM on each node. This needs to match the node name used in config.txt. The set_hostname.sh script is used when starting the runner and master erlang vms when using the supplied scripts (distributest, start_distributest_vm) NOTE:This will be made simpler in the future.

setup hooks

Inside the global_setup_scripts folder there are 2 files, node_setup and runner_setup. These two files are copied to every node participating on every test run. The node_setup file is executed in the project directory on every node before any runners start. This is useful for running bundle install on every node. The runner_setup file is executed on every runner startup. rake db:create and rake db:migrate should be located here if your testing a Rails app. The runner_setup file is passed an identifier as the first argument and should be used to name your databases so there are no clashes. Both files included in this project have examples commented out in them of exactly how they are used by the team I'm on.

config.txt

This is the main conifguration file. It includes a file glob of what tests to run, the nodes to run them on, and the amount of runners per node. Every node specified in here needs to have an ssh keypair set up from the box initiating tests. I currently support different users per node, but it needs to log in without a password for rsync.

See file for examples of how to configure the runners etc. Please copy the formatting as these are just Erlang terms and it will not work if they are not valid.

If you need to have different tests run per project you can create .distributest/config.txt in project and put your file glob there. This will override the one in /etc/distributest/config.txt NOTE:This is the only override that is supported in the per project config.txt

Ruby projects database setup

Finally, if your tests are using a database you need to edit your projects database.yml. It should look something like this.

database: <%= ENV[“DB_PREFIX”]%>distributest_test

Uncomment the last 4 lines of /etc/distributest/runner_setup as well. This will allow every runner on every node to have it's own database. Otherwise you will be blowing away your other devs test databases and having lock issues etc when X runners start pounding the same db.

Starting the application

Every system needs to have the 'runner' Erlang node started. This can be left running forever. To start this type start_distributest_vm on every node after you have installed this application and edited the set_hostname.sh as instructed above. This will be changed in the future to have a proper startup/shutdown. I recommend starting it as the user that you set in the config.txt for each particular node. If you have the same user across all the nodes it will be easier to get correct the first time.

To start the tests go to your Ruby project and type distributest.

Usage

Once you have done the initial configuration, go to your Ruby projects folder and run distributest. The code and global setup scripts will be rsynced to every node in the config.txt. It will then run the node_prep script on every node. Next it will start X runners on every node where X is specified in config.txt per node. Next each runner on each node will run the runner_setup script. Finally, every runner will start running the test files.

A log of all stdout/errout of the Ruby and Bash processes and some other logging is written to /tmp/distributest.log on the system that started the tests. The node the message came from will be at the bottom of each message. This is cleared out each run.

Speed

Distributest sorts files on a couple of things to try and get the slowest ones running first. Also, after the first run it will start sorting on the previous run time for each file.

You will very easily get your test suite time to that of the slowest test + db:migrate time. This is why it's important to run the slowest ones first.

On one project I'm working on I took a test suite that takes around 25 minutes normally down to 1:57.

Technical

Distributest was designed to be used on your fellow devs workstations/laptops etc without causing any issues. The way this works is by syncing your code to a configurable directory on every node being distributed to. The path is also keyed off the hostname of the node initiating the tests. There is also a separate database set up for every runner on every node that is keyed off the hostname of the node initiating the tests and the number of the runner. Because of this as soon as you see a test fail you can fix the issue and run the test in Textmate etc without effecting the distributed run.

I have designed this application to be fault tolerant in every aspect. If any non critical piece of this application fails on any node, the tests will continue to run. If a critical piece fails ie. you kill the main Erlang VM, it will properly kill off all Ruby processes on every node, and every process on the runner vm's on every node. The runner Erlang vm will still be running on every node and this should never go down. It only takes around 10-15 MB of memory.

When you start a projects tests a second Erlang vm will be started on the box initiating the tests. This is only alive for as long as the tests are running. It's name will be something like 'master@hostname.blah'.

Test Support

Currently this only support Rspec 1.x, but due to the way this appliction is written it should not be hard to add Rspec2, test unit etc. With a bit more work you should be able to do Python or any other language. Check out the code that the gem is built from in gem/*

I plan on adding Rspec 2 and Test Unit.

Bundler Support

In the config you can tell distributest to use bundler. If you do this you need to place distributest in your gemfile. Currently it should be set to the exact version of the app you downloaded. In the future I am going to relax this so the Erlang app can talk with any of the minor versions of the gem.

Startup issues

Note: this section will be fleshed out.
A log of info and errors is written during every run. It's located at /tmp/distributest.log on the box that is initiating the tests.  All logs from all nodes are written here.  Check it out for the initial debugging.  
If the runners are immediately dying there is a problem either loading the distributest gem or the rails application.  It can be a bit tricky tracking this down sometimes and I'm working on rescuing load errors and getting them back to the person running the tests.

Todos

  • Rewrite using OTP. I intended for this application to be a proof of concept, but it is being used in production by Rackspace and Thoughtworks now. The application can be made simpler with OTP and I intend to start working it in soon.

  • Better way to handle upgrading a cluster

  • Support more than Rspec 1.x

  • Bundler support was quickly hacked in. Currently it gos from local config. Needs to be passed in from the person running tests so we don't read the local config on any of the runners. Need to add override per app support as well.

Disclaimer

THIS WILL NOT WORK AT ALL ON WINDOWS!! You can try but don't say I didn't warn you.

I have only tested this on OSX, but I do not believe there would be any issues on any *nix variant.

I am not responsible for anything bad that happens including loss of data.

I have ran over a billion specs through this application without issue. I do not guarantee that this will happen for you. Please submit any issues you encounter after you have verified that your tests run using normal methods. Please keep in mind that if you distribute a thousand broken tests they will still be broken when ran on Distributest =) If you leave test data around you will likely see random failures. The order of tests on any given runner is not consistent as it's designed to run the entire suite as fast as possible. This can lead to random test failures where a test in one file causes a test in a following file to fail due to left over data etc. You may not see these in normal testing because it runs in the same order every time and the test causing the issue runs later.

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