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1
=================
2
Ganeti 2.3 design
3
=================
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This document describes the major changes in Ganeti 2.3 compared to
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the 2.2 version.
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.. contents:: :depth: 4
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As for 2.1 and 2.2 we divide the 2.3 design into three areas:
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- core changes, which affect the master daemon/job queue/locking or
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  all/most logical units
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- logical unit/feature changes
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- external interface changes (e.g. command line, os api, hooks, ...)
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Core changes
18
============
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Node Groups
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-----------
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Current state and shortcomings
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Currently all nodes of a Ganeti cluster are considered as part of the
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same pool, for allocation purposes: DRBD instances for example can be
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allocated on any two nodes.
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This does cause a problem in cases where nodes are not all equally
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connected to each other. For example if a cluster is created over two
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set of machines, each connected to its own switch, the internal bandwidth
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between machines connected to the same switch might be bigger than the
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bandwidth for inter-switch connections.
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Moreover some operations inside a cluster require all nodes to be locked
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together for inter-node consistency, and won't scale if we increase the
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number of nodes to a few hundreds.
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Proposed changes
41
~~~~~~~~~~~~~~~~
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With this change we'll divide Ganeti nodes into groups. Nothing will
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change for clusters with only one node group, the default one. Bigger
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cluster instead will be able to have more than one group, and each node
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will belong to exactly one.
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Node group management
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+++++++++++++++++++++
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To manage node groups and the nodes belonging to them, the following new
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commands/flags will be introduced::
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  gnt-node group-add <group> # add a new node group
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  gnt-node group-del <group> # delete an empty group
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  gnt-node group-list # list node groups
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  gnt-node group-rename <oldname> <newname> # rename a group
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  gnt-node list/info -g <group> # list only nodes belongin to a group
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  gnt-node add -g <group> # add a node to a certain group
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  gnt-node modify -g <group> # move a node to a new group
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Instance level changes
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++++++++++++++++++++++
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Instances will be able to live in only one group at a time. This is
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mostly important for DRBD instances, in which case both their primary
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and secondary nodes will need to be in the same group. To support this
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we envision the following changes:
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  - The cluster will have a default group, which will initially be
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  - Instance allocation will happen to the cluster's default group
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    (which will be changable via gnt-cluster modify or RAPI) unless a
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    group is explicitely specified in the creation job (with -g or via
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    RAPI). Iallocator will be only passed the nodes belonging to that
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    group.
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  - Moving an instance between groups can only happen via an explicit
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    operation, which for example in the case of DRBD will work by
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    performing internally a replace-disks, a migration, and a second
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    replace-disks. It will be possible to cleanup an interrupted
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    group-move operation.
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  - Cluster verify will signal an error if an instance has been left
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    mid-transition between groups.
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  - Intra-group instance migration/failover will check that the target
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    group will be able to accept the instance network/storage wise, and
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    fail otherwise. In the future we may be able to make some parameter
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    changed during the move, but in the first version we expect an
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    import/export if this is not possible.
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  - From an allocation point of view, inter-group movements will be
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    shown to a iallocator as a new allocation over the target group.
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    Only in a future version we may add allocator extensions to decide
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    which group the instance should be in. In the meantime we expect
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    Ganeti administrators to either put instances on different groups by
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    filling all groups first, or to have their own strategy based on the
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    instance needs.
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Internal changes
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++++++++++++++++
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We expect the following changes for cluster management:
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  - Frequent multinode operations, such as os-diagnose or cluster-verify
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    will act one group at a time. The default group will be used if none
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    is passed. Command line tools will have a way to easily target all
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    groups, by generating one job per group.
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  - Groups will have a human-readable name, but will internally always
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    be referenced by a UUID, which will be immutable. For example the
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    cluster object will contain the UUID of the default group, each node
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    will contain the UUID of the group it belongs to, etc. This is done
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    to simplify referencing while keeping it easy to handle renames and
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    movements. If we see that this works well, we'll transition other
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    config objects (instances, nodes) to the same model.
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  - The addition of a new per-group lock will be evaluated, if we can
113
    transition some operations now requiring the BGL to it.
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  - Master candidate status will be allowed to be spread among groups.
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    For the first version we won't add any restriction over how this is
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    done, although in the future we may have a minimum number of master
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    candidates which Ganeti will try to keep in each group, for example.
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Other work and future changes
120
+++++++++++++++++++++++++++++
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Commands like gnt-cluster command/copyfile will continue to work on the
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whole cluster, but it will be possible to target one group only by
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specifying it.
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Commands which allow selection of sets of resources (for example
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gnt-instance start/stop) will be able to select them by node group as
128
well.
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Initially node groups won't be taggable objects, to simplify the first
131
implementation, but we expect this to be easy to add in a future version
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should we see it's useful.
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We envision groups as a good place to enhance cluster scalability. In
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the future we may want to use them ad units for configuration diffusion,
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to allow a better master scalability. For example it could be possible
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to change some all-nodes RPCs to contact each group once, from the
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master, and make one node in the group perform internal diffusion. We
139
won't implement this in the first version, but we'll evaluate it for the
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future, if we see scalability problems on big multi-group clusters.
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When Ganeti will support more storage models (eg. SANs, sheepdog, ceph)
143
we expect groups to be the basis for this, allowing for example a
144
different sheepdog/ceph cluster, or a different SAN to be connected to
145
each group. In some cases this will mean that inter-group move operation
146
will be necessarily performed with instance downtime, unless the
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hypervisor has block-migrate functionality, and we implement support for
148
it (this would be theoretically possible, today, with KVM, for example).
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Scalability issues with big clusters
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------------------------------------
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Current and future issues
154
~~~~~~~~~~~~~~~~~~~~~~~~~
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Assuming the node groups feature will enable bigger clusters, other
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parts of Ganeti will be impacted even more by the (in effect) bigger
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clusters.
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While many areas will be impacted, one is the most important: the fact
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that the watcher still needs to be able to repair instance data on the
162
current 5 minutes time-frame (a shorter time-frame would be even
163
better). This means that the watcher itself needs to have parallelism
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when dealing with node groups.
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Also, the iallocator plugins are being fed data from Ganeti but also
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need access to the full cluster state, and in general we still rely on
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being able to compute the full cluster state somewhat “cheaply” and
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on-demand. This conflicts with the goal of disconnecting the different
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node groups, and to keep the same parallelism while growing the cluster
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size.
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Another issue is that the current capacity calculations are done
174
completely outside Ganeti (and they need access to the entire cluster
175
state), and this prevents keeping the capacity numbers in sync with the
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cluster state. While this is still acceptable for smaller clusters where
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a small number of allocations/removal are presumed to occur between two
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periodic capacity calculations, on bigger clusters where we aim to
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parallelise heavily between node groups this is no longer true.
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As proposed changes, the main change is introducing a cluster state
184
cache (not serialised to disk), and to update many of the LUs and
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cluster operations to account for it. Furthermore, the capacity
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calculations will be integrated via a new OpCode/LU, so that we have
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faster feedback (instead of periodic computation).
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Cluster state cache
190
~~~~~~~~~~~~~~~~~~~
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A new cluster state cache will be introduced. The cache relies on two
193
main ideas:
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- the total node memory, CPU count are very seldom changing; the total
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  node disk space is also slow changing, but can change at runtime; the
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  free memory and free disk will change significantly for some jobs, but
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  on a short timescale; in general, these values will mostly “constant”
199
  during the lifetime of a job
200
- we already have a periodic set of jobs that query the node and
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  instance state, driven the by :command:`ganeti-watcher` command, and
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  we're just discarding the results after acting on them
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Given the above, it makes sense to cache inside the master daemon the
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results of node and instance state (with a focus on the node state).
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The cache will not be serialised to disk, and will be for the most part
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transparent to the outside of the master daemon.
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Cache structure
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+++++++++++++++
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The cache will be oriented with a focus on node groups, so that it will
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be easy to invalidate an entire node group, or a subset of nodes, or the
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entire cache. The instances will be stored in the node group of their
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primary node.
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Furthermore, since the node and instance properties determine the
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capacity statistics in a deterministic way, the cache will also hold, at
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each node group level, the total capacity as determined by the new
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capacity iallocator mode.
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Cache updates
224
+++++++++++++
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226
The cache will be updated whenever a query for a node state returns
227
“full” node information (so as to keep the cache state for a given node
228
consistent). Partial results will not update the cache (see next
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paragraph).
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Since the there will be no way to feed the cache from outside, and we
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would like to have a consistent cache view when driven by the watcher,
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we'll introduce a new OpCode/LU for the watcher to run, instead of the
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current separate opcodes (see below in the watcher section).
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Updates to a node that change a node's specs “downward” (e.g. less
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memory) will invalidate the capacity data. Updates that increase the
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node will not invalidate the capacity, as we're more interested in “at
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least available” correctness, not “at most available”.
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Cache invalidations
242
+++++++++++++++++++
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244
If a partial node query is done (e.g. just for the node free space), and
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the returned values don't match with the cache, then the entire node
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state will be invalidated.
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By default, all LUs will invalidate the caches for all nodes and
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instances they lock. If an LU uses the BGL, then it will invalidate the
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entire cache. In time, it is expected that LUs will be modified to not
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invalidate, if they are not expected to change the node's and/or
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instance's state (e.g. ``LUConnectConsole``, or
253
``LUActivateInstanceDisks``).
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Invalidation of a node's properties will also invalidate the capacity
256
data associated with that node.
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258
Cache lifetime
259
++++++++++++++
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261
The cache elements will have an upper bound on their lifetime; the
262
proposal is to make this an hour, which should be a high enough value to
263
cover the watcher being blocked by a medium-term job (e.g. 20-30
264
minutes).
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Cache usage
267
+++++++++++
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269
The cache will be used by default for most queries (e.g. a Luxi call,
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without locks, for the entire cluster). Since this will be a change from
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the current behaviour, we'll need to allow non-cached responses,
272
e.g. via a ``--cache=off`` or similar argument (which will force the
273
query).
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The cache will also be used for the iallocator runs, so that computing
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allocation solution can proceed independent from other jobs which lock
277
parts of the cluster. This is important as we need to separate
278
allocation on one group from exclusive blocking jobs on other node
279
groups.
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281
The capacity calculations will also use the cache—this is detailed in
282
the respective sections.
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Watcher operation
285
~~~~~~~~~~~~~~~~~
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287
As detailed in the cluster cache section, the watcher also needs
288
improvements in order to scale with the the cluster size.
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As a first improvement, the proposal is to introduce a new OpCode/LU
291
pair that runs with locks held over the entire query sequence (the
292
current watcher runs a job with two opcodes, which grab and release the
293
locks individually). The new opcode will be called
294
``OpUpdateNodeGroupCache`` and will do the following:
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- try to acquire all node/instance locks (to examine in more depth, and
297
  possibly alter) in the given node group
298
- invalidate the cache for the node group
299
- acquire node and instance state (possibly via a new single RPC call
300
  that combines node and instance information)
301
- update cache
302
- return the needed data
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304
The reason for the per-node group query is that we don't want a busy
305
node group to prevent instance maintenance in other node
306
groups. Therefore, the watcher will introduce parallelism across node
307
groups, and it will possible to have overlapping watcher runs. The new
308
execution sequence will be:
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310
- the parent watcher process acquires global watcher lock
311
- query the list of node groups (lockless or very short locks only)
312
- fork N children, one for each node group
313
- release the global lock
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- poll/wait for the children to finish
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316
Each forked children will do the following:
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318
- try to acquire the per-node group watcher lock
319
- if fail to acquire, exit with special code telling the parent that the
320
  node group is already being managed by a watcher process
321
- otherwise, submit a OpUpdateNodeGroupCache job
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- get results (possibly after a long time, due to busy group)
323
- run the needed maintenance operations for the current group
324

    
325
This new mode of execution means that the master watcher processes might
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overlap in running, but not the individual per-node group child
327
processes.
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This change allows us to keep (almost) the same parallelism when using a
330
bigger cluster with node groups versus two separate clusters.
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Cost of periodic cache updating
334
+++++++++++++++++++++++++++++++
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336
Currently the watcher only does “small” queries for the node and
337
instance state, and at first sight changing it to use the new OpCode
338
which populates the cache with the entire state might introduce
339
additional costs, which must be payed every five minutes.
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341
However, the OpCodes that the watcher submits are using the so-called
342
dynamic fields (need to contact the remote nodes), and the LUs are not
343
selective—they always grab all the node and instance state. So in the
344
end, we have the same cost, it just becomes explicit rather than
345
implicit.
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347
This ‘grab all node state’ behaviour is what makes the cache worth
348
implementing.
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Intra-node group scalability
351
++++++++++++++++++++++++++++
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353
The design above only deals with inter-node group issues. It still makes
354
sense to run instance maintenance for nodes A and B if only node C is
355
locked (all being in the same node group).
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357
This problem is commonly encountered in previous Ganeti versions, and it
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should be handled similarly, by tweaking lock lifetime in long-duration
359
jobs.
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361
TODO: add more ideas here.
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State file maintenance
365
++++++++++++++++++++++
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367
The splitting of node group maintenance to different children which will
368
run in parallel requires that the state file handling changes from
369
monolithic updates to partial ones.
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There are two file that the watcher maintains:
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- ``$LOCALSTATEDIR/lib/ganeti/watcher.data``, its internal state file,
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  used for deciding internal actions
375
- ``$LOCALSTATEDIR/run/ganeti/instance-status``, a file designed for
376
  external consumption
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For the first file, since it's used only internally to the watchers, we
379
can move to a per node group configuration.
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381
For the second file, even if it's used as an external interface, we will
382
need to make some changes to it: because the different node groups can
383
return results at different times, we need to either split the file into
384
per-group files or keep the single file and add a per-instance timestamp
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(currently the file holds only the instance name and state).
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The proposal is that each child process maintains its own node group
388
file, and the master process will, right after querying the node group
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list, delete any extra per-node group state file. This leaves the
390
consumers to run a simple ``cat instance-status.group-*`` to obtain the
391
entire list of instance and their states. If needed, the modify
392
timestamp of each file can be used to determine the age of the results.
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394

    
395
Capacity calculations
396
~~~~~~~~~~~~~~~~~~~~~
397

    
398
Currently, the capacity calculations are done completely outside
399
Ganeti. As explained in the current problems section, this needs to
400
account better for the cluster state changes.
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402
Therefore a new OpCode will be introduced, ``OpComputeCapacity``, that
403
will either return the current capacity numbers (if available), or
404
trigger a new capacity calculation, via the iallocator framework, which
405
will get a new method called ``capacity``.
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407
This method will feed the cluster state (for the complete set of node
408
group, or alternative just a subset) to the iallocator plugin (either
409
the specified one, or the default is none is specified), and return the
410
new capacity in the format currently exported by the htools suite and
411
known as the “tiered specs” (see :manpage:`hspace(1)`).
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413
tspec cluster parameters
414
++++++++++++++++++++++++
415

    
416
Currently, the “tspec” calculations done in :command:`hspace` require
417
some additional parameters:
418

    
419
- maximum instance size
420
- type of instance storage
421
- maximum ratio of virtual CPUs per physical CPUs
422
- minimum disk free
423

    
424
For the integration in Ganeti, there are multiple ways to pass these:
425

    
426
- ignored by Ganeti, and being the responsibility of the iallocator
427
  plugin whether to use these at all or not
428
- as input to the opcode
429
- as proper cluster parameters
430

    
431
Since the first option is not consistent with the intended changes, a
432
combination of the last two is proposed:
433

    
434
- at cluster level, we'll have cluster-wide defaults
435
- at node groups, we'll allow overriding the cluster defaults
436
- and if they are passed in via the opcode, they will override for the
437
  current computation the values
438

    
439
Whenever the capacity is requested via different parameters, it will
440
invalidate the cache, even if otherwise the cache is up-to-date.
441

    
442
The new parameters are:
443

    
444
- max_inst_spec: (int, int, int), the maximum instance specification
445
  accepted by this cluster or node group, in the order of memory, disk,
446
  vcpus;
447
- default_template: string, the default disk template to use
448
- max_cpu_ratio: double, the maximum ratio of VCPUs/PCPUs
449
- max_disk_usage: double, the maximum disk usage (as a ratio)
450

    
451
These might also be used in instance creations (to be determined later,
452
after they are introduced).
453

    
454
OpCode details
455
++++++++++++++
456

    
457
Input:
458

    
459
- iallocator: string (optional, otherwise uses the cluster default)
460
- cached: boolean, optional, defaults to true, and denotes whether we
461
  accept cached responses
462
- the above new parameters, optional; if they are passed, they will
463
  overwrite all node group's parameters
464

    
465
Output:
466

    
467
- cluster: list of tuples (memory, disk, vcpu, count), in decreasing
468
  order of specifications; the first three members represent the
469
  instance specification, the last one the count of how many instances
470
  of this specification can be created on the cluster
471
- node_groups: a dictionary keyed by node group UUID, with values a
472
  dictionary:
473

    
474
  - tspecs: a list like the cluster one
475
  - additionally, the new cluster parameters, denoting the input
476
    parameters that were used for this node group
477

    
478
- ctime: the date the result has been computed; this represents the
479
  oldest creation time amongst all node groups (so as to accurately
480
  represent how much out-of-date the global response is)
481

    
482
Note that due to the way the tspecs are computed, for any given
483
specification, the total available count is the count for the given
484
entry, plus the sum of counts for higher specifications.
485

    
486
Also note that the node group information is provided just
487
informationally, not for allocation decisions.
488

    
489

    
490
Job priorities
491
--------------
492

    
493
Current state and shortcomings
494
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
495

    
496
Currently all jobs and opcodes have the same priority. Once a job
497
started executing, its thread won't be released until all opcodes got
498
their locks and did their work. When a job is finished, the next job is
499
selected strictly by its incoming order. This does not mean jobs are run
500
in their incoming order—locks and other delays can cause them to be
501
stalled for some time.
502

    
503
In some situations, e.g. an emergency shutdown, one may want to run a
504
job as soon as possible. This is not possible currently if there are
505
pending jobs in the queue.
506

    
507
Proposed changes
508
~~~~~~~~~~~~~~~~
509

    
510
Each opcode will be assigned a priority on submission. Opcode priorities
511
are integers and the lower the number, the higher the opcode's priority
512
is. Within the same priority, jobs and opcodes are initially processed
513
in their incoming order.
514

    
515
Submitted opcodes can have one of the priorities listed below. Other
516
priorities are reserved for internal use. The absolute range is
517
-20..+19. Opcodes submitted without a priority (e.g. by older clients)
518
are assigned the default priority.
519

    
520
  - High (-10)
521
  - Normal (0, default)
522
  - Low (+10)
523

    
524
As a change from the current model where executing a job blocks one
525
thread for the whole duration, the new job processor must return the job
526
to the queue after each opcode and also if it can't get all locks in a
527
reasonable timeframe. This will allow opcodes of higher priority
528
submitted in the meantime to be processed or opcodes of the same
529
priority to try to get their locks. When added to the job queue's
530
workerpool, the priority is determined by the first unprocessed opcode
531
in the job.
532

    
533
If an opcode is deferred, the job will go back to the "queued" status,
534
even though it's just waiting to try to acquire its locks again later.
535

    
536
If an opcode can not be processed after a certain number of retries or a
537
certain amount of time, it should increase its priority. This will avoid
538
starvation.
539

    
540
A job's priority can never go below -20. If a job hits priority -20, it
541
must acquire its locks in blocking mode.
542

    
543
Opcode priorities are synchronized to disk in order to be restored after
544
a restart or crash of the master daemon.
545

    
546
Priorities also need to be considered inside the locking library to
547
ensure opcodes with higher priorities get locks first. See
548
:ref:`locking priorities <locking-priorities>` for more details.
549

    
550
Worker pool
551
+++++++++++
552

    
553
To support job priorities in the job queue, the worker pool underlying
554
the job queue must be enhanced to support task priorities. Currently
555
tasks are processed in the order they are added to the queue (but, due
556
to their nature, they don't necessarily finish in that order). All tasks
557
are equal. To support tasks with higher or lower priority, a few changes
558
have to be made to the queue inside a worker pool.
559

    
560
Each task is assigned a priority when added to the queue. This priority
561
can not be changed until the task is executed (this is fine as in all
562
current use-cases, tasks are added to a pool and then forgotten about
563
until they're done).
564

    
565
A task's priority can be compared to Unix' process priorities. The lower
566
the priority number, the closer to the queue's front it is. A task with
567
priority 0 is going to be run before one with priority 10. Tasks with
568
the same priority are executed in the order in which they were added.
569

    
570
While a task is running it can query its own priority. If it's not ready
571
yet for finishing, it can raise an exception to defer itself, optionally
572
changing its own priority. This is useful for the following cases:
573

    
574
- A task is trying to acquire locks, but those locks are still held by
575
  other tasks. By deferring itself, the task gives others a chance to
576
  run. This is especially useful when all workers are busy.
577
- If a task decides it hasn't gotten its locks in a long time, it can
578
  start to increase its own priority.
579
- Tasks waiting for long-running operations running asynchronously could
580
  defer themselves while waiting for a long-running operation.
581

    
582
With these changes, the job queue will be able to implement per-job
583
priorities.
584

    
585
.. _locking-priorities:
586

    
587
Locking
588
+++++++
589

    
590
In order to support priorities in Ganeti's own lock classes,
591
``locking.SharedLock`` and ``locking.LockSet``, the internal structure
592
of the former class needs to be changed. The last major change in this
593
area was done for Ganeti 2.1 and can be found in the respective
594
:doc:`design document <design-2.1>`.
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596
The plain list (``[]``) used as a queue is replaced by a heap queue,
597
similar to the `worker pool`_. The heap or priority queue does automatic
598
sorting, thereby automatically taking care of priorities. For each
599
priority there's a plain list with pending acquires, like the single
600
queue of pending acquires before this change.
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602
When the lock is released, the code locates the list of pending acquires
603
for the highest priority waiting. The first condition (index 0) is
604
notified. Once all waiting threads received the notification, the
605
condition is removed from the list. If the list of conditions is empty
606
it's removed from the heap queue.
607

    
608
Like before, shared acquires are grouped and skip ahead of exclusive
609
acquires if there's already an existing shared acquire for a priority.
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To accomplish this, a separate dictionary of shared acquires per
611
priority is maintained.
612

    
613
To simplify the code and reduce memory consumption, the concept of the
614
"active" and "inactive" condition for shared acquires is abolished. The
615
lock can't predict what priorities the next acquires will use and even
616
keeping a cache can become computationally expensive for arguable
617
benefit (the underlying POSIX pipe, see ``pipe(2)``, needs to be
618
re-created for each notification anyway).
619

    
620
The following diagram shows a possible state of the internal queue from
621
a high-level view. Conditions are shown as (waiting) threads. Assuming
622
no modifications are made to the queue (e.g. more acquires or timeouts),
623
the lock would be acquired by the threads in this order (concurrent
624
acquires in parentheses): ``threadE1``, ``threadE2``, (``threadS1``,
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``threadS2``, ``threadS3``), (``threadS4``, ``threadS5``), ``threadE3``,
626
``threadS6``, ``threadE4``, ``threadE5``.
627

    
628
::
629

    
630
  [
631
    (0, [exc/threadE1, exc/threadE2, shr/threadS1/threadS2/threadS3]),
632
    (2, [shr/threadS4/threadS5]),
633
    (10, [exc/threadE3]),
634
    (33, [shr/threadS6, exc/threadE4, exc/threadE5]),
635
  ]
636

    
637

    
638
IPv6 support
639
------------
640

    
641
Currently Ganeti does not support IPv6. This is true for nodes as well
642
as instances. Due to the fact that IPv4 exhaustion is threateningly near
643
the need of using IPv6 is increasing, especially given that bigger and
644
bigger clusters are supported.
645

    
646
Supported IPv6 setup
647
~~~~~~~~~~~~~~~~~~~~
648

    
649
In Ganeti 2.3 we introduce additionally to the ordinary pure IPv4
650
setup a hybrid IPv6/IPv4 mode. The latter works as follows:
651

    
652
- all nodes in a cluster have a primary IPv6 address
653
- the master has a IPv6 address
654
- all nodes **must** have a secondary IPv4 address
655

    
656
The reason for this hybrid setup is that key components that Ganeti
657
depends on do not or only partially support IPv6. More precisely, Xen
658
does not support instance migration via IPv6 in version 3.4 and 4.0.
659
Similarly, KVM does not support instance migration nor VNC access for
660
IPv6 at the time of this writing.
661

    
662
This led to the decision of not supporting pure IPv6 Ganeti clusters, as
663
very important cluster operations would not have been possible. Using
664
IPv4 as secondary address does not affect any of the goals
665
of the IPv6 support: since secondary addresses do not need to be
666
publicly accessible, they need not be globally unique. In other words,
667
one can practically use private IPv4 secondary addresses just for
668
intra-cluster communication without propagating them across layer 3
669
boundaries.
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671
netutils: Utilities for handling common network tasks
672
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
673

    
674
Currently common util functions are kept in the utils modules. Since
675
this module grows bigger and bigger network-related functions are moved
676
to a separate module named *netutils*. Additionally all these utilities
677
will be IPv6-enabled.
678

    
679
Cluster initialization
680
~~~~~~~~~~~~~~~~~~~~~~
681

    
682
As mentioned above there will be two different setups in terms of IP
683
addressing: pure IPv4 and hybrid IPv6/IPv4 address. To choose that a
684
new cluster init parameter *--primary-ip-version* is introduced. This is
685
needed as a given name can resolve to both an IPv4 and IPv6 address on a
686
dual-stack host effectively making it impossible to infer that bit.
687

    
688
Once a cluster is initialized and the primary IP version chosen all
689
nodes that join have to conform to that setup. In the case of our
690
IPv6/IPv4 setup all nodes *must* have a secondary IPv4 address.
691

    
692
Furthermore we store the primary IP version in ssconf which is consulted
693
every time a daemon starts to determine the default bind address (either
694
*0.0.0.0* or *::*. In a IPv6/IPv4 setup we need to bind the Ganeti
695
daemon listening on network sockets to the IPv6 address.
696

    
697
Node addition
698
~~~~~~~~~~~~~
699

    
700
When adding a new node to a IPv6/IPv4 cluster it must have a IPv6
701
address to be used as primary and a IPv4 address used as secondary. As
702
explained above, every time a daemon is started we use the cluster
703
primary IP version to determine to which any address to bind to. The
704
only exception to this is when a node is added to the cluster. In this
705
case there is no ssconf available when noded is started and therefore
706
the correct address needs to be passed to it.
707

    
708
Name resolution
709
~~~~~~~~~~~~~~~
710

    
711
Since the gethostbyname*() functions do not support IPv6 name resolution
712
will be done by using the recommended getaddrinfo().
713

    
714
IPv4-only components
715
~~~~~~~~~~~~~~~~~~~~
716

    
717
============================  ===================  ====================
718
Component                     IPv6 Status          Planned Version
719
============================  ===================  ====================
720
Xen instance migration        Not supported        Xen 4.1: libxenlight
721
KVM instance migration        Not supported        Unknown
722
KVM VNC access                Not supported        Unknown
723
============================  ===================  ====================
724

    
725

    
726
Privilege Separation
727
--------------------
728

    
729
Current state and short comings
730
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
731

    
732
As of Ganeti 2.2 we introduced privilege separation. This was affecting
733
just Ganeti RAPI and also that just in a quickly short term solution. In
734
this release we iterate again over it and make it more advanced and
735
stable. This also means we'll remove the privilege separation again from
736
the core and put it completely external so the daemons will be started
737
on the final user already.
738

    
739
Additionally this involves removing SSH code out auf bootstrap and core
740
component and put it into a separate script. This means every
741
daemon/script will assume that a working ssh setup is in place.
742

    
743
Implementation
744
~~~~~~~~~~~~~~
745

    
746
We need to partially revert changes done in Ganeti 2.2 to move on the
747
long term solution. This involves removing the drop privileges code in
748
``daemons.py`` as this is already done on startup time by
749
``start-stop-daemon`` util.
750

    
751
The ssh code will be separated into one single script called upon
752
``gnt-node add`` which guarantees that the SSH setup is done and
753
functioning.
754

    
755
Additionally some of the utils.WriteFile calls needs to be adjusted
756
for the new permissions and ownerships.
757

    
758
Security Domains
759
~~~~~~~~~~~~~~~~
760

    
761
In order to separate the permissions of file sets we separate them
762
into the following 3 overall security domain chunks:
763

    
764
1. Public: ``0755`` respectively ``0644``
765
2. Ganeti wide: shared between the daemons (gntdaemons)
766
3. Secret files: shared just between a specified set of daemons/users
767

    
768
So for point 3 this tables shows the correlation of the sets to groups
769
and their users:
770

    
771
=== ========== ============================== ==========================
772
Set Group      Users                          Description
773
=== ========== ============================== ==========================
774
A   gntrapi    gntrapi, gntmasterd            Share data between
775
                                              gntrapi & gntmasterd
776
B   gntadmins  gntrapi, gntmasterd, *users*   Shared between users who
777
                                              needs to call gntmasterd
778
C   gntconfd   gntconfd, gntmasterd           Share data between
779
                                              gntconfd & gntmasterd
780
D   gntmasterd gntmasterd                     masterd only; Currently
781
                                              only to redistribute the
782
                                              configuration, has access
783
                                              to all files under
784
                                              ``lib/ganeti``
785
E   gntdaemons gntmasterd, gntrapi, gntconfd  Shared between the various
786
                                              Ganeti daemons to exchange
787
                                              data
788
=== ========== ============================== ==========================
789

    
790
Restricted commands
791
~~~~~~~~~~~~~~~~~~~
792

    
793
The following commands needs still root to fulfill their functions:
794

    
795
::
796

    
797
  gnt-cluster {init|destroy|command|copyfile|rename|masterfailover|renew-crypto}
798
  gnt-node {add|remove}
799
  gnt-instance {console}
800

    
801
Directory structure & permissions
802
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
803

    
804
Here's how we propose to change the filesystem hierachy and their
805
permissions.
806

    
807
Assuming it follows the defaults: ``gnt${daemon}`` for user and
808
the groups from the section `Security Domains`_::
809

    
810
  ${localstatedir}/lib/ganeti/ (0755; gntmasterd:gntmasterd)
811
     cluster-domain-secret (0600; gntmasterd:gntmasterd)
812
     config.data (0640; gntmasterd:gntconfd)
813
     hmac.key (0440; gntmasterd:gntconfd)
814
     known_host (0644; gntmasterd:gntmasterd)
815
     queue/ (0700; gntmasterd:gntmasterd)
816
       archive/ (0700; gntmasterd:gntmasterd)
817
         * (0600; gntmasterd:gntmasterd)
818
       * (0600; gntmasterd:gntmasterd)
819
     rapi.pem (0440; gntrapi:gntrapi)
820
     rapi_users (0640; gntrapi:gntrapi)
821
     server.pem (0440; gntmasterd:gntmasterd)
822
     ssconf_* (0444; root:gntmasterd)
823
     uidpool/ (0750; root:gntmasterd)
824
     watcher.data (0600; root:gntmasterd)
825
  ${localstatedir}/run/ganeti/ (0770; gntmasterd:gntdaemons)
826
     socket/ (0750; gntmasterd:gntadmins)
827
       ganeti-master (0770; gntmasterd:gntadmins)
828
  ${localstatedir}/log/ganeti/ (0770; gntmasterd:gntdaemons)
829
     master-daemon.log (0600; gntmasterd:gntdaemons)
830
     rapi-daemon.log (0600; gntrapi:gntdaemons)
831
     conf-daemon.log (0600; gntconfd:gntdaemons)
832
     node-daemon.log (0600; gntnoded:gntdaemons)
833

    
834

    
835
Feature changes
836
===============
837

    
838

    
839
External interface changes
840
==========================
841

    
842

    
843
.. vim: set textwidth=72 :
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.. Local Variables:
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.. mode: rst
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.. fill-column: 72
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.. End: