Riak Test

Welcome to the exciting world of riak_test.

What is Riak Test?

riak_test is a system for testing Riak clusters. Tests are written in Erlang, and can interact with the cluster using distributed Erlang.

How does it work?

riak_test runs tests in a sandbox, typically $HOME/rt/riak. The sanbox uses git to reset back to a clean state after tests are run. The contents of $HOME/rt/riak might look something like this:

$ ls $HOME/rt/riak
current riak-1.1.4 riak-1.2.1 riak-1.3.2

Inside each of these directories is a dev folder, typically created with your normal make [stage]devrel. So how does this sandbox get populated to begin with?

You'll create another directory that will contain full builds of different version of Riak for your platform. Typically this directory has been ~/test-releases but it can be called anything and be anywhere that you'd like. The dev/ directory from each of these releases will be copied into the sandbox ($HOME/rt/riak). There are helper scripts in bin/ which will help you get both ~/test-releases and $HOME/rt/riak all set up. A full tutorial for using them exists further down in this README.

There is one folder in $HOME/rt/riak that does not come from ~/test-releases: current. The current folder can refer to any version of Riak, but is typically used for something like the master branch, a feature branch, or a release candidate. The $HOME/rt/riak/current dev release gets populated from a devrel of Riak that can come from anywhere, but is usually your 'normal' git checkout of Riak. The bin/rtdev-current.sh can be run from within that folder to copy dev/ into $HOME/rt/riak/current.

Once you have everything set up (again, instructions for this are below), you'll want to run and write tests. This repository also holds code for an Erlang application called riak_test. The actual tests exist in the test/ directory.

Bootstraping Your Test Environment

Running tests against a development version of Riak is just one of the things that you can do with riak_test. You can also test things involving upgrading from previous versions of Riak. Together, we'll get your test environment up and running. Scripts to help in this process are located in the bin directory of this project.

rtdev-all.sh

This script is for the lazy. It performs all of the setup steps described in the other scripts, including installing the current "master" branch from Github into "current". The releases will be built in your current working directory, so create an empty one in a place you'd like to store these builds for posterity, so that you don't have to rebuild them if your installation path ($HOME/rt/riak by the way this script installs it) gets into a bad state.

If you do want to restore your $HOME/rt/riak folder to factory condition, see rtdev-setup-releases.sh and if you want to change the current riak under test, see rtdev-current.sh.

rtdev-build-releases.sh

The first one that we want to look at is rtdev-build-releases.sh. If left unchanged, this script is going to do the following:

1. Download the source for the past three major Riak versions (e.g. 1.1.4, 1.2.1 and 1.3.2)
2. Build the proper version of Erlang that release was built with, using kerl (which it will also download)
3. Build those releases of Riak.

You'll want to run this script from an empty directory. Also, you might be thinking that you already have all the required versions of erlang. Great! You can crack open the script and set the paths to your installation:

R14B04=${R14B04:-$HOME/erlang-R14B04}
R15B01=${R15B01:-$HOME/erlang-R15B01}
R15B03=${R15B03:-$HOME/erlang-R15B03}

Kerlveat: If you want kerl to build erlangs with serious 64-bit macintosh action, you'll need a ~/.kerlrc file that looks like this:

KERL_CONFIGURE_OPTIONS="--disable-hipe --enable-smp-support --enable-threads --enable-kernel-poll  --enable-darwin-64bit"

The script will check that all these paths exist. If even one of them is missing, it will prompt you to install kerl, even if you already have kerl. If you say no, the script quits. If you say yes, or all of your erlang paths check out, then go get a cup of coffee, you'll be building for a little while.

rtdev-setup-releases.sh

The rtdev-setup-releases.sh will get the releases you just built into a local git repository. Currently, running this script from the same directory that you just built all of your releases into. Currently this script initializes this repository into $HOME/rt/riak but it's probably worth making that configurable in the near term.

rtdev-current.sh

rtdev-current.sh is where it gets interesting. You need to run that from the Riak source folder you're wanting to test as the current version of Riak. Also, make sure that you've already run make devrel or make stagedevrel before you run rtdev-current.sh.

Config file.

Now that you've got your releases all ready and gitified, you'll need to tell riak_test about them. The method of choice is to create a ~/.riak_test.config that looks something like this:

{default, [
    {giddyup_host, "localhost:5000"},
    {giddyup_user, "user"},
    {giddyup_password, "password"},
    {rt_max_wait_time, 600000},
    {rt_retry_delay, 1000},
    {rt_harness, rtdev},
    {rt_scratch_dir, "/tmp/riak_test_scratch"},
    {basho_bench, "/home/you/basho/basho_bench"},
    {spam_dir, "/home/you/basho/riak_test/search-corpus/spam.0"},
    {platform, "osx-64"}
]}.

{rtdev, [
    {rt_project, "riak"},
    {rtdev_path, [{root,     "/home/you/rt/riak"},
                  {current,  "/home/you/rt/riak/current"},
                  {previous, "/home/you/rt/riak/riak-1.3.2"},
                  {legacy,   "/home/you/rt/riak/riak-1.2.1"}
                 ]}
]}.

The default section of the config file will be overridden by the config name you specify. For example, running the command below will use an rt_retry_delay of 500 and an rt_max_wait_time of 180000. If your defaults contain every option you need, you can run riak_test without the -c argument.

Some configuration parameters:

rt_default_config

Default configuration parameters that will be used for nodes deployed by riak_test. Tests can override these.

{rtdev, [
    { rt_default_config,
        [ {riak_core, [ {ring_creation_size, 16} ]} ] }
]}

Running riak_test for the first time

Run a test! ./riak_test -c rtdev -t verify_build_cluster

Did that work? Great, try something harder: ./riak_test -c rtdev_mixed -t upgrade

Intercepts

Intercepts are a powerful but easy to wield feature. They allow you to change the behavior of any function and affect global state in an extremely lightweight manner. You can modify the KV vnode to simulate dropped puts. You can sleep a call to discover what happens when certain calls take a long time to finish. You can even turn a call into a noop to really cause havoc on a cluster. These are just some examples. You should also be able to change any function you want, including dependency functions and even Erlang functions. Furthermore, any state you can reach from a function call can be affected such as function arguments but also ETS tables. This leads to the principle of intercepts.

If you can do it in Riak source code you can do it with an intercept.

Writing Intercepts

Writing an intercept is nearly identical to writing any other Erlang source with a few easy to remember conventions added.

1. All intercepts must live under the intercepts dir.

2. All intercept modules should be named the same as the module they affect with the suffix _intercepts added. E.g. riak_kv_vnode => riak_kv_vnode_intercepts.

3. All intercept modules should include the intercept.hrl file. This includes macros to properly log messages. You cannot call lager.

4. All intercept modules should declare the macro M who's value is the affected module with the suffix _orig added. E.g. for riak_kv_vnode add the line -define(M, riak_kv_vnode_orig). This, along with the next convention is needed to call into the original function.

5. To call the origin function use the ?M: follow by the name of the function with the _orig suffix appended. E.g. to call riak_kv_vnode:put you would type ?M:put_orig.

6. To log a message use the I_ macros. E.g. to log an info message use ?I_INFO.

The easiest way to understand the above conventions is to see them all at work in an example.

-module(riak_kv_vnode_intercepts).
-compile(export_all).
-include("intercept.hrl").
-define(M, riak_kv_vnode_orig).

dropped_put(Preflist, BKey, Obj, ReqId, StartTime, Options, Sender) ->
    NewPreflist = lists:sublist(Preflist, length(Preflist) - 1),
    ?I_INFO("Preflist modified from ~p to ~p", [Preflist, NewPreflist]),
    ?M:put_orig(NewPreflist, BKey, Obj, ReqId, StartTime, Options, Sender).

How Do I Use Intercepts?

Intercepts can be used in two ways: 1) added via the config, 2) added via rpc:call in the test. The first way is most convenient, is persistent (survives node restarts), and is in effect for all tests. The second method requires additional code, is specific to a test, is ephemeral (does not survive a node restart), but allows more fine grained control.

In both cases intercepts can be disabled by adding the following to your config. By default intercepts will be loaded and compiled, but not added. That is, they will be available but not in effect unless you add them via one of the methods listed previously.

{load_intercepts, false}

Config

Here is how you would add the dropped_put intercept via the config.

{intercepts, [{riak_kv_vnode, [{{put,7}, dropped_put}]}]}

Breaking this down, the config key is intercepts and its value is a list of intercepts to add. Each intercept definition in the list describes which functions to intercept and what functions to intercept them with. The example above would result in all calls to riak_kv_vnode:put/7 being intercepted by riak_kv_vnode_intercepts:dropped_put/7.

{ModuleToIntercept, [{{FunctionToIntercept, Arity}, InterceptFunction}]}

Manual

To add the dropped_put intercept manually you would do the following.

`rt_intercept:add(Node, {riak_kv_vnode, [{{put,7}, dropped_put}]})`

How Does it Work?

Knowing the implementation details is not needed to use intercepts but this knowledge could come in handy if problems are encountered. There are two parts to understand: 1) how the intercept code works and 2) how intercepts are applied on-the-fly in Riak Test. It's important to keep one thing in mind.

Intercepts are based entirely on code generation and hot-swapping. The overhead of an intercept is always 1 or 2 function calls. 1 if a function is not being intercepted, 2 if it is and you call the original function.

The intercept code turns your original module into three. Based on the mapping passed to intercept:add code is generated to re-route requests to your intercept code or forward them to the original code. E.g. if defining intercepts on riak_kv_vnode the following modules will exist.

• riak_kv_vnode_orig - Contains the original code from riak_kv_vnode but modified so that all original functions have the suffix _orig added to them and the original function definitions become passthrus to riak_kv_vnode, the proxy.

• riak_kv_vnode_intercepts - This contains code of your intercept as you defined it. No modification of the code is performed.

• riak_kv_vnode - What once contained the original code is now a proxy. All functions passthru to riak_kv_vnode_orig. Unless an intercept is registered in the mapping passed to intercept:add. In that case the call will forward to riak_kv_vnode_intercepts.

The interceptor code also modifies the original module and proxy to export all functions. This fact, along with the fact that all the original functions in riak_kv_vnode_orig will callback into the proxy, means that you can intercept private functions as well.

In order for Riak Test to use intercepts they need to be compiled, loaded, and registered on the nodes under test. You can't use the bytecode generated by Riak Tests' rebar because the Erlang version used will often be different from that included with your Riak nodes. You could require that the user compile with the oldest Erlang version supported but that is extra burden on the user and still doesn't guarantee things will work if there is a jump of more than 2 majors in Erlang version. No, this should be easy to use and thus the intercept code is compiled on the Riak nodes guaranteeing that the bytecode will be compatible.

After the code is compiled and loaded the intercepts need to be added. All intercepts defined in the user's riak_test.config will be added automatically any time a node is started. Thus, intercepts defined in the config survive restarts and are essentially always in play. A user can also manually add an intercept by making an rpc call from the test code to the remote node. This method is ephemeral and the intercept will not survive restarts.