Cob

Cob, yet another yum S3 plugin, provides a way to accessing yum repositories hosted on AWS S3.

What's the difference between Cob and original yum s3 plugin?

• Support more secure AWS Signature Version 4 while original one still in version 2, especially for the new region eu-central-1 only SigV4 allowed
• Hook on higher layer of Yum built-in library to avoid complicated low-level handlings
• Support static AWS credentials prior to IAM role
• Add retry mechanism to fetch IAM role credentials

Quick Start

• Installation

  • ./install.sh
  • plugin conf: cob.conf --> /etc/yum/pluginconf.d/cob.conf
  • plugin code: cob.py --> /usr/lib/yum-plugins/cob.py

• Setup minimal IAM Role Policy for Cob

  {
    "Statement": [
      {
        "Effect": "Allow",
        "Action": [
          "s3:GetObject"
        ],
        "Resource": "*"
      }
    ]
  }

  • For cross-account access, setup the policy of yum s3 bucket

    {
      "Version": "2008-10-17",
      "Statement": [
        {
          "Effect": "Allow",
          "Principal": {
            "AWS": [
              "arn:aws:iam::37ABC0340XYZ:root",
              "arn:aws:iam::24ABC3058XYZ:root"
            ]
          },
          "Action": "s3:GetObject",
          "Resource": "arn:aws:s3:::yum-s3-bucket-XYZ/*"
        }
      ]
    }

    • "37ABC0340XYZ", "24ABC3058XYZ": AWS account id with the permission to access
    • "yum-s3-bucket-XYZ": S3 bucket for yum access

• Configure your yum repo conf under /etc/yum.repos.d/, like the example below cob.repo

  [cob]
  name=cob
  baseurl=https://your-bucket-name-0.s3.amazonaws.com/repo-name/arch/
          https://your-bucket-name-1.s3-eu-west-1.amazonaws.com/repo-name/arch/
          https://your-bucket-name-2.s3-us-west-2.amazonaws.com/repo-name/arch/
  failovermethod=priority
  enabled=1
  gpgcheck=0

  • add the bucket region name in the baseurl as shown in the example, especially for us-east-1, like your-bucket-name-0, no region name needed there
  • s3 endpoint reference: http://docs.aws.amazon.com/general/latest/gr/rande.html#s3_region

• An example from cob.conf is taken to indicate its usages:

  [main]
  cachedir=/var/cache/yum/$basearch/$releasever
  keepcache=1
  debuglevel=4
  logfile=/var/log/yum.log
  exactarch=1
  obsoletes=0
  gpgcheck=0
  plugins=1
  distroverpkg=centos-release
  enabled=1
  
  [aws]
  # access_key = 
  # secret_key =
  timeout = 60
  retries = 5
  metadata_server = http://169.254.169.254

  • set main/enabled=1 to enable this yum plugin
  • for static AWS credentials, you could specify via aws/access_key, aws/secret_key
  • aws/timeout and aws/retries, used to indicate params in the way of fetching IAM role credentials
  • metadata_server used to help testing

• Enable verbose log to help troubleshoot the Cob issue:

  URLGRABBER_DEBUG=1 yum -v makecache