Preparation

In this section, you will start building a blockchain to play the checkers game. You will build it natively with Cosmos SDK v0.50. At least, you will build some initial elements.

This section uses the following repositories:

• A minimal Cosmos v0.50 app with no extra modules, found here (opens new window).
• A minimal v0.50 module example, found here (opens new window).

Version 0.50 of the Cosmos SDK was created, in part, with a view to facilitate module integration. This section seeks to demonstrate that. In particular, you will keep your checkers module separate from the (minimal) app.

Install

Before you can start building, you need to prepare your computer. The simplest way is to rely on Docker (opens new window), as the Cosmos team has prepared a Docker image for developers (opens new window) built via this Dockerfile (opens new window). If you need a refresher on Docker, head here.

You will also need to have make (opens new window) on your computer.

The minimal app

Since you are building off the minimal app, clone it locally:

Copy $ git clone https://github.com/cosmosregistry/chain-minimal.git --branch mini-v050 $ cd chain-minimal $ git checkout -b main

You can already confirm that it compiles and runs correctly. You need Go version 1.21. To compile it, run:

Copy $ make install

Make use of scripts/init.sh to set it up with test values:

Copy $ make init

Run it:

Copy $ minid start

You should see the familiar log:

Copy ... 7:03PM INF finalized block block_app_hash=25D4020CCCE016BFC606F4904334EF3E81F60A283F694FC5F11B0F1F9850EA83 height=1 module=state num_txs_res=0 num_val_updates=0 7:03PM INF executed block app_hash=25D4020CCCE016BFC606F4904334EF3E81F60A283F694FC5F11B0F1F9850EA83 height=1 module=state ...

In another shell, you can confirm the list of modules that are included:

Copy $ minid query --help

This confirms that your minimal chain is working as expected. You can stop it with CTRL-C.

The module example

Since you are going to copy a (small) number of files from the module example, it is convenient to have a local copy somewhere:

Copy $ git clone https://github.com/cosmosregistry/example.git --branch v0.1.0 minimal-module-example $ cd minimal-module-example $ git checkout -b main

Moreover, your checkers module is going to be named github.com/alice/checkers, so to make your file copying even easier you can use the provided renaming script:

Copy $ MODULE_NAME=alice/checkers ./scripts/rename.sh

The updated files will come in handy when you want to copy-paste them.

1

The rename.sh files self-removes when the process is complete. If an error happens, you may have to reset hard with Git before retrying:

Copy $ git reset --hard

This assumes that you have no other uncommitted changes that are worth keeping.

2

If you get something like:

Copy /usr/bin/env: 'bash\r': No such file or directory

Note that the \r points to line endings. Try changing the script's line endings from Windows to Unix/Linux style, or vice-versa.

Up next

With the minimal chain and a copy of the minimal module, it is time to build your own module.