[Gluster-devel] [Gluster-users] Proposal for GlusterD-2.0

[Pranith Kumar Karampuri]

On 09/05/2014 03:51 PM, Kaushal M wrote:
> GlusterD performs the following functions as the management daemon for 
> GlusterFS:
> - Peer membership management
> - Maintains consistency of configuration data across nodes 
> (distributed configuration store)
> - Distributed command execution (orchestration)
> - Service management (manage GlusterFS daemons)
> - Portmap service for GlusterFS daemons
>
>
> This proposal aims to delegate the above functions to technologies 
> that solve these problems well. We aim to do this in a phased manner.
> The technology alternatives we would be looking for should have the 
> following properties,
> - Open source
> - Vibrant community
> - Good documentation
> - Easy to deploy/manage
>
> This would allow GlusterD's architecture to be more modular. We also 
> aim to make GlusterD's architecture as transparent and observable as 
> possible. Separating out these functions would allow us to do that.
>
> Bulk of current GlusterD code deals with keeping the configuration of 
> the cluster and the volumes in it consistent and available across the 
> nodes. The current algorithm is not scalable  (N^2 in no. of nodes) 
> and doesn't prevent split-brain of configuration. This is the problem 
> area we are targeting for the first phase.
>
> As part of the first phase, we aim to delegate the distributed 
> configuration store. We are exploring consul [1] as a replacement for 
> the existing distributed configuration store (sum total of 
> /var/lib/glusterd/* across all nodes). Consul provides distributed 
> configuration store which is consistent and partition tolerant. By 
> moving all Gluster related configuration information into consul we 
> could avoid split-brain situations.
Did you get a chance to go over the following questions while making the 
decision? If yes could you please share the info.
What are the consistency guarantees for changing the configuration in 
case of network partitions?
      specifically when there are 2 nodes and 1 of them is not reachable?
      consistency guarantees when there are more than 2 nodes?
What are the consistency guarantees for reading configuration in case of 
network partitions?

Pranith
>
> All development efforts towards this proposal would happen in parallel 
> to the existing GlusterD code base. The existing code base would be 
> actively maintained until GlusterD-2.0 is production-ready.
>
> This is in alignment with the GlusterFS Quattro proposals on making 
> GlusterFS scalable and easy to deploy. This is the first phase ground 
> work towards that goal.
>
> Questions and suggestions are welcome.
>
> ~kaushal
>
> [1] : http://www.consul.io/
>
>
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