Despite this, I've seen that LDAP is not widely used. Is this for its complexity or are there deeper reasons that suggest to use SQL database for both (user data, accounting) purposes? Does anybody have links that might help to build a system made using this architecture?
I use ldap for users and sql for accounting for the same reasons you listed. Installing and using openldap has a much higher learning curve than mysql, which is why I would guess more users use mysql. There is an old doc in the source under doc/ldap_howto.txt. I wrote that several years ago and keep promising a new version. Well, I was finally given a week at the end of this month or early next month to stop all my projects and start documenting. So, at that time, I will be re-writing that doc to be more current. I agree that ldap is a perfect place to store user objects. For example, I have it setup like this. ou=users uid=someuser,ou=users... radiusgroupname: dial radiusgroupname: adsl accountNumber: 11111 uid=anotheruser,ou=users... radiusgroupname: adsl accountNumber: 11111 ou=accounts accountNumber=11111,ou=accounts... radiusgroupname: wifi Using ldap, I can specify the services the user has access to as an attribute of that user. I can also do account level groups as well. In the users above, with my freeradius configuration, I can assure that someuser has access to adsl and dial, while another user can only login to adsl. Any user in the 11111 account can login to wifi, which would be both of those users. Now, you can easily do the same thing in mysql as well. But, I feel that ldap is a better model for this data. Also, with openldap it is very easy to replicate and setup distribution of these users. Also, since ldap is a standard protocol, my provisioning system can write to it whether its from windows, solaris, linux, etc... It just needs to understand the ldap protocol. Using mysql, means your provisioning system must understand mysql syntax, although that isn't usually a difficult task to get setup. Finally, as you said, ldap is optimized for reads and that's exactly what I'm doing. I've never experienced any issues with the ldap servers being overloaded. Then again I don't get a whole lot of traffic maybe 60k-80k logins a day. The only downside I can think of with openldap is that it doesn't support multi-master setups. There are workarounds I've heard of people using with some kind of heartbeat setup and a shared IP, but I don't have the need for a multi-master setup. As long as my master is replicating to my slaves and freeradius is hitting my slaves, I can assure that no users are ever denied access because of an ldap server going down. If the master goes down, the only effect is on provisioning (such as adding new users or changing passwords). In this case we take a slave server and manually upgrade it to a master while we fix the master server. Freeradius with its configurable_failover solution, will allow us to point to all of our slave servers and it takes care of any slave servers going down automatically for us, without the need for a load balancer. As an alternative for non-freeradius ldap queries, I've also setup two ldap proxy servers that point back to my three slaves. The two proxy servers share an IP, so one is always master (on the ip). If it goes down, the slave takes over that IP. In that scenario, you can point applications that don't do failover to the proxyldap shared IP and it will take care of the failover for you. I really like ldap, but its taken me some time to become comfortable with it. I hope that doc helps you with your setup, if you need more help, post questions to the list. Be sure to explain what you are trying to do and show debug info (radiusd -X) so we can see the difference between what its doing and what you want it to do. Take care.