`AWS_REGION` vs `REGION` environment variables

In `.ebextensions/options.config` it is the `AWS_REGION` environment variable that is set, but in `app.js`, the code refers to the `REGION` environment variable to set `AWS.config.region`. Inspection of running system on launched EB environment shows that indeed `REGION` is actually not set.

Although the code still appears to work, I believe that the intention was to say `AWS.config.region = process.env.AWS_REGION` instead (otherwise `AWS_REGION` is not used anywhere). I'm a bit puzzled as to why the code still works when `AWS.config.region` is set to undefined (especially after one switches to use `nodejs-tutorial` for table name). How does the running process know to use the correct region in this case?

Compare the AWS_REGION setting in .ebextensions/options.config with the REGION lookup in app.js, then inspect how the running Elastic Beanstalk process obtains its region. Verify the intended variable is used consistently and confirm the sample still starts and accesses its configured table in the expected region.

索引モデルが issue の本文から書いたものです。