Load Balancing Databases with Rails

One of the most common reasons for using LDAP is to integrate into an existing authentication structure. If an LDAP server is provided for a Windows domain, this will allow the web application to authenticate users against that domain rather than maintaining its own user models separately.

Set up the ldap.yml file as described previously (without specifyinga password), but do not bind to the LDAP server from environment.rb. We will perform the bind as part of the authentication process. The following code is adapted from the Rails wiki:*

  class LdapUser < ActiveLDAP::Base
    ldap_mapping :prefix => (LDAP prefix for your users)

    LDAP_PATH = File.join(RAILS_ROOT,"config","ldap.yml")
    LDAP_CONFIG = YAML.load(File.read(ldap_path))[RAILS_ENV]

    def self.authenticate username, password
      begin 
       ActiveLDAP::Base.establish_connection(config.merge(
         :bind_format => "uid=#{username},cn=users,dc=mycompany,dc=com",
         :password => password,
         :allow_anonymous => false

      ))
      ActiveLDAP::Base.close
      return true

      rescue ActiveLDAP::AuthenticationError
        return false
      end
    end
  end

Authentication is then very simple:

  LdapUser.authenticate "my_username", "password" # => true or false

Further Reading

Chris Date's Database in Depth (OReilly) is a very accessible introduction to relational theory aimed at software developers who are experienced in the use of relational databases. It reintroduces readers into the technical foundations behind the relational model.

Theo Schlossnagle's Scalable Internet Architectures (Sams) is a short but comprehensive treatment of ways to accomplish scalability (both high availability and load balancing are covered); it covers ground from the smallest two-server failover cluster up to global server load balancing.

Both the MySQL manual (http://dev.mysql.com/doc/) and the PostgreSQL manual (http://www.postgresql.org/docs/) have a wealth of information about general database topics, as well as specific information pertaining to the use of those DBMSs.

* Informally, DBMSs are often referred to as “databases." Consistent with industry practices, in this book "database management system" refers to the software package or installation thereof, while "database" refers to the actual data set being managed.

* Technically pronounced "post-gres-Q-L," and usually just called "Postgres." This is a contender for the least intuitive name in computing today. It has its roots in PostgreSQL’s long-ago predecessor, Postgres, which did not support SQL.

* ACID stands for Atomic, Consistent, Isolated, and Durable, which are necessary properties for transactional integrity within a database. See http://en.wikipedia.org/wiki/ACID for a full definition and explanation.

† Instructions are at http://wiki.rubyonrails.org/rails/pages/ HowtoConnectToMicrosoftSQLServerFromRailsOnLinux;
FreeTDS is available from http://www.freetds.org/.

* Short for "byte array."

† Assuming fairly uniform binary data, the BYTEA quoting rules lead to an average expansion ratio of 1:2.9.

‡ The size is defined in LOBLKSIZE. It defaults to 2 KB.

* http://celebnamer.celebworld.ws/stuff/ mod_xsendfile/

* http://cleanair.highgroove.com/articles/ 2006/10/03/mini-file-uploads

* http://www.martinfowler.com/bliki/ DatabaseStyles.html

* I would probably keep that one at the application level, because it contains the business rule that no employee’s salary is zero. However, "an employee’s salary must be non-negative" would most likely be an
integrity constraint, as it is nearly inconceivable that you would "pay" an employee a negative salary.

† http://drysql.rubyforge.org/

* Pronounced "mem-cache-dee," for "memory cache daemon." Available from http://danga.com/memcached/.

* http://wiki.rubyonrails.org/rails/pages/ HowtoAuthenticateViaLdap