+.. [*] Note that no run-time data is present for offline, drained or
+ non-vm_capable nodes; this means the tags total_memory,
+ reserved_memory, free_memory, total_disk, free_disk, total_cpus,
+ i_pri_memory and i_pri_up memory will be absent
+
+Operation-specific input
+++++++++++++++++++++++++
+
+All input dictionaries to the IAllocator carry, in the ``request``
+dictionary, detailed information about the operation that's being
+requested. The required keys vary depending on the type of operation, as
+follows.
+
+In all cases, it includes:
+
+ type
+ the request type; this can be either ``allocate``, ``relocate``,
+ ``change-group`` or ``node-evacuate``. The
+ ``allocate`` request is used when a new instance needs to be placed
+ on the cluster. The ``relocate`` request is used when an existing
+ instance needs to be moved within its node group.
+
+ The ``multi-evacuate`` protocol used to request that the script
+ computes the optimal relocate solution for all secondary instances
+ of the given nodes. It is now deprecated and needs only be
+ implemented if backwards compatibility with Ganeti 2.4 and lower is
+ needed.
+
+ The ``change-group`` request is used to relocate multiple instances
+ across multiple node groups. ``node-evacuate`` evacuates instances
+ off their node(s). These are described in a separate :ref:`design
+ document <multi-reloc-detailed-design>`.
+
+For both allocate and relocate mode, the following extra keys are needed
+in the ``request`` dictionary:
+
+ name
+ the name of the instance; if the request is a realocation, then this
+ name will be found in the list of instances (see below), otherwise
+ is the FQDN of the new instance; type *string*
+
+ required_nodes
+ how many nodes should the algorithm return; while this information
+ can be deduced from the instace's disk template, it's better if
+ this computation is left to Ganeti as then allocator scripts are
+ less sensitive to changes to the disk templates; type *integer*
+
+ disk_space_total
+ the total disk space that will be used by this instance on the
+ (new) nodes; again, this information can be computed from the list
+ of instance disks and its template type, but Ganeti is better
+ suited to compute it; type *integer*
+
+.. pyassert::
+
+ constants.DISK_ACCESS_SET == set([constants.DISK_RDONLY,
+ constants.DISK_RDWR])
+
+Allocation needs, in addition: