[Freeipa-users] replication again :-(

[Ludwig Krispenz]

On 05/21/2015 03:28 PM, Janelle wrote:
> I think I found the problem.
>
> There was a lone replica running in another DC. It was installed as a 
> replica some time ago with all the others.  Think of this -- the 
> original config had 5 servers, one of them was this server. Then the 
> other 4 servers were RE-BUILT from scratch, so all the replication 
> agreements were changed AND - this is the important part - the 5th 
> server was never added back in. BUT - the 5th server was left running 
> and never told it that it was not a member anymore. It still thought 
> it had a replication agreement with original "server 1", but server 1 
> knew otherwise.
>
> Now, although the first 4 servers were rebuilt, the same domain, 
> realm, AND passwords were used.
>
> I am guessing that somehow, this 5th server keeps trying to interject 
> its info into the ring of 4 servers, kind of forcing its way in. 
> Somehow, because the original credentials still work (but certs are 
> all different) is leaving the first 4 servers with a "can't decode" 
> issue.
>
> There should be some security checks so this can't happen. It should 
> also be easy to replicate.
>
> Now I have to go re-initialize all the servers from a good server, so 
> everyone is happy again. The "problem" server has been shutdown 
> completely. (and yes, there were actually 3 of them in my scenario - I 
> just used 1 to simplify my example - but that explains the 3 CSNs that 
> just kept "appearing")
>
> What concerns me most about this - were the servers outside of the 
> "good ring" somehow able to inject data into replication which might 
> have been causing bad data??? This is bad if it is true.
it depends a bit on what you mean by rebuilt from scratch.
A replication session needs to meet three conditions to be able to send 
data:
- the supplier side needs to be able to authenticate and the 
authenticated users has to be in the list of binddns of the replica
-  the data generation of supplier and consumer side need to be the same 
(they all have to have the same common origin)
- the supplier needs to have the changes (CSNs) to be able to position 
in its changelog to send updates

now if you have 5 servers, forget about one of them and do not change 
the credentials in the others and do not reinitialize the database by an 
ldif import to generate a new database generation, the fifth server will 
still be able to connect and eventually send updates - how should the 
other servers know that this one is no longer a "good" one
>
> ~Janelle
>