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From Jared Cantwell <jared.cantw...@gmail.com>
Subject Re: Dynamic reconfiguration
Date Sat, 28 Jul 2012 22:26:08 GMT
Having to "make up" a configuration for new servers that are non voting followers is something
I keep getting stuck on, because if a couple of these servers start with just the wrong configuration
they can all have an unspecified version and actually form a standalone quorum and not know
a newer one exists. I would feel much better if new servers that are to become non voting
followers could simply copy the configuration file from an existing voting participant (including
 the version) and still start up. This is particularly an issue for us because servers with
arbitrarily old configurations can start up at any time, and if the wrong things happen then
they could form a quorum if they have the right "bootstrap" configurations with unspecified

Does this make sense as a concern? We may patch the server to allow starting up without its
myid in the configuration. 


On Jul 28, 2012, at 12:15 PM, Alexander Shraer <shralex@gmail.com> wrote:

> yes, if the server reboots (this is when it would read the config file). 
> Otherwise, it has the last config in memory (this is held in a QuorumVerifier object
in QuorumPeer) and it doesn't look in the config file. 
> BTW the config file (when overwritten by the system) has an auto-generated version using
which we know which config is later than which.  Users are not supposed to specify this version
at all - its supposed to be managed by the system. If you replace the file and set the version
to something low or not specify it at all, chances are that the config file will be overwritten
during synchronization with the leader or during communication with other servers in FastLeaderElection.
> If you set it to something high, its possible that your server will be able to convince
others that this is the latest config :)
> Alex
> On Sat, Jul 28, 2012 at 10:57 AM, Jared Cantwell <jared.cantwell@gmail.com> wrote:
> No that you would want to do this, but simply overwriting a config file would "uncommit"
a configuration and make that server think the last committed configuration was whatever is
in the file?

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