Installing Custom Code

Riak supports the use of Erlang named functions in compiled modules for pre/post-commit hooks, and MapReduce operations. This doc contains installation steps with simple examples for each use case.

Your developers can compile custom erlang code, which they can send to you as a beam file. You should note that in Erlang, a file name must have the same name the module. So if you are given a file named validate_json.beam, do not rename it.

Note: The Configure step (add_paths) also applies to installing JavaScript files.


If you have been given Erlang code and are expected to compile it for your developers, keep the following notes in mind.

Note on the Erlang Compiler

You must use the Erlang compiler (erlc) associated with the Riak installation or the version of Erlang used when compiling Riak from source. For packaged Riak installations, you can consult Table 1 below for the default location of Riak’s erlc for each supported platform. If you compiled from source, use the erlc from the Erlang version you used to compile Riak.

CentOS & RHEL Linux


Debian & Ubuntu Linux






Solaris 10


Table 1: Erlang compiler executable location for packaged Riak installations on supported platforms

Compiling the module is a straightforward process.

erlc validate_json.erl

Next, you’ll need to define a path from which compiled modules can be stored and loaded. For our example, we’ll use a temporary directory /tmp/beams, but you should choose a directory for production functions based on your own requirements such that they will be available where and when needed.

Ensure that the directory chosen above can be read by the riak user.

Successful compilation will result in a new .beam file, validate_json.beam.


Take the validate_json.beam and copy this file to the /tmp/beams directory.

cp validate_json.beam /tmp/beams/

After copying the compiled module into /tmp/beams/, you must update app.config and configure Riak to allow loading of compiled modules from the directory where they’re stored (again in our example case, /tmp/beams).

Edit app.config and insert an add_paths setting into the riak_kv section as shown:

{riak_kv, [
  %% ...
  {add_paths, ["/tmp/beams/"]},
  %% ...

After updating app.config, Riak must be restarted. In production cases, you should ensure that if you are adding configuration changes to multiple nodes, that you do so in a rolling fashion, taking time to ensure that the Riak key value store has fully initialized and become available for use.

This is done with the riak-admin wait-for-service command as detailed in the Commands documentation.

It is important that you ensure riak_kv is active before restarting the next node.