ruby/rubygems · error · Gem::S3URISigner::ConfigurationError

no key for host #{host} in s3_source in .gemrc

Error message

no key for host #{host} in s3_source in .gemrc

What it means

Error "no key for host #{host} in s3_source in .gemrc" thrown in ruby/rubygems.

Source

Thrown at lib/rubygems/s3_uri_signer.rb:118

  def generate_signature(s3_config, date, string_to_sign)
    date_key = OpenSSL::HMAC.digest("sha256", "AWS4" + s3_config.secret_access_key, date)
    date_region_key = OpenSSL::HMAC.digest("sha256", date_key, s3_config.region)
    date_region_service_key = OpenSSL::HMAC.digest("sha256", date_region_key, "s3")
    signing_key = OpenSSL::HMAC.digest("sha256", date_region_service_key, "aws4_request")
    OpenSSL::HMAC.hexdigest("sha256", signing_key, string_to_sign)
  end

  ##
  # Extracts S3 configuration for S3 bucket
  def fetch_s3_config
    return S3Config.new(uri.user, uri.password, nil, "us-east-1") if uri.user && uri.password

    s3_source = Gem.configuration[:s3_source] || Gem.configuration["s3_source"]
    host = uri.host
    raise ConfigurationError.new("no s3_source key exists in .gemrc") unless s3_source

    auth = s3_source[host] || s3_source[host.to_sym]
    raise ConfigurationError.new("no key for host #{host} in s3_source in .gemrc") unless auth

    provider = auth[:provider] || auth["provider"]
    case provider
    when "env"
      id = ENV["AWS_ACCESS_KEY_ID"]
      secret = ENV["AWS_SECRET_ACCESS_KEY"]
      security_token = ENV["AWS_SESSION_TOKEN"]
    when "instance_profile"
      credentials = ec2_metadata_credentials_json
      id = credentials["AccessKeyId"]
      secret = credentials["SecretAccessKey"]
      security_token = credentials["Token"]
    else
      id = auth[:id] || auth["id"]
      secret = auth[:secret] || auth["secret"]
      security_token = auth[:security_token] || auth["security_token"]
    end

View on GitHub (pinned to 86cbb817a3)

Solutions

1. Add an entry for the reported host under s3_source in ~/.gemrc

When it happens

Trigger: Thrown at lib/rubygems/s3_uri_signer.rb:118 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of ruby/rubygems@86cbb817a3 (2026-08-23). Data as JSON: /api/errors/dd929d57c036ff95. Report an issue: GitHub.