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From "Jens Alfke (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (COUCHDB-1259) Replication ID is not stable if local server has a dynamic port number
Date Mon, 05 Nov 2012 04:33:12 GMT

    [ https://issues.apache.org/jira/browse/COUCHDB-1259?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13490448#comment-13490448
] 

Jens Alfke commented on COUCHDB-1259:
-------------------------------------

It seems like overkill to get the IANA to assign a fixed port number to an app that doesn't
even listen on any external interfaces! The only use of that port is (was) over the loopback
interface to let the application communicate with CouchDB.

Passing zero for the port in the config file didn't make the problem go away. Apparently the
replicator bases the ID on the actual random port number in use, not on the fixed 0 from the
config.

> What will prevents an hostile node to connect back to your node with the same id?

Hello, are you listening at all to what I'm writing? I've already said several times that
the app does not accept incoming connections at all. It only makes outgoing connections to
replicate.

And in general: obviously in any real P2P app there would be actual security measures in place
to authenticate connections, most likely by using both server and client SSL certs and verifying
their public keys. Once the connection is made, _then_ database IDs can be used to restore
the state of a replication.
                
> Replication ID is not stable if local server has a dynamic port number
> ----------------------------------------------------------------------
>
>                 Key: COUCHDB-1259
>                 URL: https://issues.apache.org/jira/browse/COUCHDB-1259
>             Project: CouchDB
>          Issue Type: Bug
>          Components: Replication
>    Affects Versions: 1.1
>            Reporter: Jens Alfke
>            Assignee: Robert Newson
>            Priority: Blocker
>             Fix For: 1.3
>
>         Attachments: couchdb-1259.patch, couchdb-1259.patch
>
>
> I noticed that when Couchbase Mobile running on iOS replicates to/from a remote server
(on iriscouch in this case), the replication has to fetch the full _changes feed every time
it starts. Filipe helped me track down the problem -- the replication ID is coming out different
every time. The reason for this is that the local port number, which is one of the inputs
to the hash that generates the replication ID, is randomly assigned by the OS. (I.e. it uses
a port number of 0 when opening its listener socket.) This is because there could be multiple
apps using Couchbase Mobile running on the same device and we can't have their ports colliding.
> The underlying problem is that CouchDB is attempting to generate a unique ID for a particular
pair of {source, destination} databases, but it's basing it on attributes that aren't fundamental
to the database and can change, like the hostname or port number.
> One solution, proposed by Filipe and me, is to assign each database (or each server?)
a random UUID when it's created, and use that to generate replication IDs.
> Another solution, proposed by Damien, is to have CouchDB let the client work out the
replication ID on its own, and set it as a property in the replication document (or the JSON
body of a _replicate request.) This is even more flexible and will handle tricky scenarios
like full P2P replication where there may be no low-level way to uniquely identify the remote
database being synced with.

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