From 0fa74e9f1e491e01d0d51af694bcd8598cf499f4 Mon Sep 17 00:00:00 2001 From: Constantinos Venetsanopoulos <cven@grnet.gr> Date: Thu, 20 Feb 2014 13:18:56 +0200 Subject: [PATCH] docs: Regions, Zones, Clusters and VM mobility Add a section in the Admin Guide documenting mobility and failure domains: Regions, Zones, Clusters. --- docs/admin-guide.rst | 106 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 106 insertions(+) diff --git a/docs/admin-guide.rst b/docs/admin-guide.rst index 5fe94741a..fc62d098e 100644 --- a/docs/admin-guide.rst +++ b/docs/admin-guide.rst @@ -2536,6 +2536,112 @@ Node10: All sections: :ref:`Scale out Guide <i-synnefo>` +Regions, Zones and Clusters +=========================== + +Region +------ + +A Region is a single Synnefo installation, with +Compute/Network/Image/Volume/Object Store services. A Region is associated with +one set of Synnefo DBs (Astakos DB, Pithos DB and Cyclades DB). Every Region has a +distinct set of API endpoints, e.g., +`https://cloud.example.com/cyclades/compute/v2.0`. Two Regions are most times +located geographically far from each other, e.g. "Europe", "US-East". A Region +comprises multiple Zones. + +Zone +---- + +A Zone is a set of Ganeti clusters, in a potentially geographically distinct +location, e.g. "Athens", "Rome". All clusters have access to the same physical +networks, and are considered a single failure domain, e.g., they access the +network over the same router. A Zone comprises muliple Ganeti clusters. + +Ganeti cluster +-------------- + +A Ganeti cluster is a set of Ganeti nodes (physical machines). One of the nodes +has the role of "Ganeti master". If this node goes down, another node may +undertake the master role. Ganeti nodes run Virtual Machines (VMs). VMs can live +migrate inside a Ganeti cluster. A Ganeti cluster comprises multiple physical +hardware nodes, most times geographically close to each other. + +VM mobility +----------- + +VMs may move across Regions, Zones, Ganeti clusters and physical nodes. Before we +describe how that's possible, we will describe the different kinds of moving, +providing the corresponding terminology: + +Live migration +~~~~~~~~~~~~~~ + +The act of moving a running VM from physical node to physical node without any +impact on its operation. The VM continues to run on its new physical location, +completely unaffected, and without any service downtime or dropped connections. +Live migration typically requires shared storage and networking between the source +and destination nodes. + +Live migration is issued by the administrator in the background and is transparent +to the VM user. + +Failover +~~~~~~~~ + +The act of moving a VM from physical node to physical node by stopping it first on +the source node, then re-starting it on the destination node. There is short +service downtime, during the time the VM boots up, and client connections are +dropped. + +Failover is issued by the administrator in the background and the VM user will +experience a reboot. + +Snapshot Failover +~~~~~~~~~~~~~~~~~ + +The act of moving a VM from physical node to physical node via a point-in-time +snapshot. That is, stopping a VM on the source node, taking a snapshot, then +creating a new VM from that snapshot. + +Snapshot failover is issued by the VM user and not the administrator. + +Disaster Recovery +----------------- + +In Synnefo terminology, Disaster Recovery is the process of sustaining a disaster +in one datacenter, and ensuring business continuity by performing live migration +or failover of running/existing VMs, or respawning VMs from previously made +snapshots. Based on the method used, this can work inside a single Ganeti cluster, +across Ganeti clusters in the same Zone, or across Zones. + +Specifically: + +Live migration is only supported inside a single Ganeti cluster. Ganeti supports +live migration between nodes in the same cluster with or without shared storage. +Live migration is done at the Ganeti level and is transparent to Synnefo. + +Failover is supported inside a Ganeti cluster, across Ganeti clusters and across +Zones. Ganeti supports failover inside a Ganeti cluster with or without shared +storage, which poses minimum downtime for the VM. Failover inside the same Ganeti +cluster is done at the Ganeti level and is transparent to Synnefo. + +Ganeti also provides tools for failing over VMs across different Ganeti clusters, +meaning that one can use them to failover VMs across Ganeti clusters of the same +Zone or across Ganeti clusters of different Zones, thus moving across Zones. +Failing over across different Ganeti clusters requires copying of data, resulting +in longer downtimes, depending on the geographical distance and network between +them. Failover across Ganeti clusters, either in the same or different Zones, is +not transparent to Synnefo and requires manual import of intances at Synnefo level +too, by the administrator. + +Snapshot failover supports moving VMs across all domains. It is issued by the VM +user and is done at the Synnefo level without the need of running anything at the +Ganeti level or by the administrator. + +In the future Synnefo will also support moving VMs across different Regions. + + Upgrade Notes ============= -- GitLab