This instruction is to install Extension:AWS for MediaWiki 1.27-1.34 (old versions of MediaWiki). If you use MediaWiki 1.35+, see Extension:AWS#Installation instead.

Installation for 1.27-1.34

1. Download the extension:

   git clone --depth 1 -b REL1_34 https://github.com/edwardspec/mediawiki-aws-s3.git AWS

2. Move the AWS directory to the "extensions" directory of your MediaWiki, e.g. /var/www/html/w/extensions (assuming MediaWiki is in /var/www/html/w).
3. Run composer install from /var/www/html/w/extensions/AWS (to download dependencies). If you don't have Composer installed, see Composer for how to install it.
4. Create an S3 bucket for images, e.g. wonderfulbali234.

   Note: this name will be seen in URL of images.

5. Authorize MediaWiki to access Amazon S3:
   1. If your EC2 instance has an IAM instance profile (recommended), copy everything from "Needed IAM permissions" (see below) to inline policy of the IAM role. See https://console.aws.amazon.com/iam/home#/roles
   2. If your EC2 instance doesn't have an IAM profile, obtain key/secret for AWS API. You'll need to write it in LocalSettings.php (see below).
6. Modify LocalSettings.php (see below).

See https://github.com/edwardspec/mediawiki-aws-s3/blob/master/README.md for more details.