root / doc / iallocator.rst @ 1e98bac2
History | View | Annotate | Download (15.9 kB)
1 |
Ganeti automatic instance allocation |
---|---|
2 |
==================================== |
3 |
|
4 |
Documents Ganeti version 2.4 |
5 |
|
6 |
.. contents:: |
7 |
|
8 |
Introduction |
9 |
------------ |
10 |
|
11 |
Currently in Ganeti the admin has to specify the exact locations for |
12 |
an instance's node(s). This prevents a completely automatic node |
13 |
evacuation, and is in general a nuisance. |
14 |
|
15 |
The *iallocator* framework will enable automatic placement via |
16 |
external scripts, which allows customization of the cluster layout per |
17 |
the site's requirements. |
18 |
|
19 |
User-visible changes |
20 |
~~~~~~~~~~~~~~~~~~~~ |
21 |
|
22 |
There are two parts of the ganeti operation that are impacted by the |
23 |
auto-allocation: how the cluster knows what the allocator algorithms |
24 |
are and how the admin uses these in creating instances. |
25 |
|
26 |
An allocation algorithm is just the filename of a program installed in |
27 |
a defined list of directories. |
28 |
|
29 |
Cluster configuration |
30 |
~~~~~~~~~~~~~~~~~~~~~ |
31 |
|
32 |
At configure time, the list of the directories can be selected via the |
33 |
``--with-iallocator-search-path=LIST`` option, where *LIST* is a |
34 |
comma-separated list of directories. If not given, this defaults to |
35 |
``$libdir/ganeti/iallocators``, i.e. for an installation under |
36 |
``/usr``, this will be ``/usr/lib/ganeti/iallocators``. |
37 |
|
38 |
Ganeti will then search for allocator script in the configured list, |
39 |
using the first one whose filename matches the one given by the user. |
40 |
|
41 |
Command line interface changes |
42 |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
43 |
|
44 |
The node selection options in instanece add and instance replace disks |
45 |
can be replace by the new ``--iallocator=NAME`` option (shortened to |
46 |
``-I``), which will cause the auto-assignement of nodes with the |
47 |
passed iallocator. The selected node(s) will be show as part of the |
48 |
command output. |
49 |
|
50 |
IAllocator API |
51 |
-------------- |
52 |
|
53 |
The protocol for communication between Ganeti and an allocator script |
54 |
will be the following: |
55 |
|
56 |
#. ganeti launches the program with a single argument, a filename that |
57 |
contains a JSON-encoded structure (the input message) |
58 |
|
59 |
#. if the script finishes with exit code different from zero, it is |
60 |
considered a general failure and the full output will be reported to |
61 |
the users; this can be the case when the allocator can't parse the |
62 |
input message |
63 |
|
64 |
#. if the allocator finishes with exit code zero, it is expected to |
65 |
output (on its stdout) a JSON-encoded structure (the response) |
66 |
|
67 |
Input message |
68 |
~~~~~~~~~~~~~ |
69 |
|
70 |
The input message will be the JSON encoding of a dictionary containing |
71 |
all the required information to perform the operation. We explain the |
72 |
contents of this dictionary in two parts: common information that every |
73 |
type of operation requires, and operation-specific information. |
74 |
|
75 |
Common information |
76 |
++++++++++++++++++ |
77 |
|
78 |
All input dictionaries to the IAllocator must carry the following keys: |
79 |
|
80 |
version |
81 |
the version of the protocol; this document |
82 |
specifies version 2 |
83 |
|
84 |
cluster_name |
85 |
the cluster name |
86 |
|
87 |
cluster_tags |
88 |
the list of cluster tags |
89 |
|
90 |
enabled_hypervisors |
91 |
the list of enabled hypervisors |
92 |
|
93 |
request |
94 |
a dictionary containing the details of the request; the keys vary |
95 |
depending on the type of operation that's being requested, as |
96 |
explained in `Operation-specific input`_ below. |
97 |
|
98 |
nodegroups |
99 |
a dictionary with the data for the cluster's node groups; it is keyed |
100 |
on the group UUID, and the values are a dictionary with the following |
101 |
keys: |
102 |
|
103 |
name |
104 |
the node group name |
105 |
alloc_policy |
106 |
the allocation policy of the node group (consult the semantics of |
107 |
this attribute in the :manpage:`gnt-group(8)` manpage) |
108 |
|
109 |
instances |
110 |
a dictionary with the data for the current existing instance on the |
111 |
cluster, indexed by instance name; the contents are similar to the |
112 |
instance definitions for the allocate mode, with the addition of: |
113 |
|
114 |
admin_up |
115 |
if this instance is set to run (but not the actual status of the |
116 |
instance) |
117 |
|
118 |
nodes |
119 |
list of nodes on which this instance is placed; the primary node |
120 |
of the instance is always the first one |
121 |
|
122 |
nodes |
123 |
dictionary with the data for the nodes in the cluster, indexed by |
124 |
the node name; the dict contains [*]_ : |
125 |
|
126 |
total_disk |
127 |
the total disk size of this node (mebibytes) |
128 |
|
129 |
free_disk |
130 |
the free disk space on the node |
131 |
|
132 |
total_memory |
133 |
the total memory size |
134 |
|
135 |
free_memory |
136 |
free memory on the node; note that currently this does not take |
137 |
into account the instances which are down on the node |
138 |
|
139 |
total_cpus |
140 |
the physical number of CPUs present on the machine; depending on |
141 |
the hypervisor, this might or might not be equal to how many CPUs |
142 |
the node operating system sees; |
143 |
|
144 |
primary_ip |
145 |
the primary IP address of the node |
146 |
|
147 |
secondary_ip |
148 |
the secondary IP address of the node (the one used for the DRBD |
149 |
replication); note that this can be the same as the primary one |
150 |
|
151 |
tags |
152 |
list with the tags of the node |
153 |
|
154 |
master_candidate: |
155 |
a boolean flag denoting whether this node is a master candidate |
156 |
|
157 |
drained: |
158 |
a boolean flag denoting whether this node is being drained |
159 |
|
160 |
offline: |
161 |
a boolean flag denoting whether this node is offline |
162 |
|
163 |
i_pri_memory: |
164 |
total memory required by primary instances |
165 |
|
166 |
i_pri_up_memory: |
167 |
total memory required by running primary instances |
168 |
|
169 |
group: |
170 |
the node group that this node belongs to |
171 |
|
172 |
No allocations should be made on nodes having either the ``drained`` |
173 |
or ``offline`` flags set. More details about these of node status |
174 |
flags is available in the manpage :manpage:`ganeti(7)`. |
175 |
|
176 |
.. [*] Note that no run-time data is present for offline, drained or |
177 |
non-vm_capable nodes; this means the tags total_memory, |
178 |
reserved_memory, free_memory, total_disk, free_disk, total_cpus, |
179 |
i_pri_memory and i_pri_up memory will be absent |
180 |
|
181 |
Operation-specific input |
182 |
++++++++++++++++++++++++ |
183 |
|
184 |
All input dictionaries to the IAllocator carry, in the ``request`` |
185 |
dictionary, detailed information about the operation that's being |
186 |
requested. The required keys vary depending on the type of operation, as |
187 |
follows. |
188 |
|
189 |
In all cases, it includes: |
190 |
|
191 |
type |
192 |
the request type; this can be either ``allocate``, ``relocate``, |
193 |
``multi-relocate`` or ``multi-evacuate``. The ``allocate`` request |
194 |
is used when a new instance needs to be placed on the cluster. The |
195 |
``relocate`` request is used when an existing instance needs to be |
196 |
moved within its node group. |
197 |
|
198 |
The ``multi-evacuate`` protocol used to request that the script |
199 |
computes the optimal relocate solution for all secondary instances |
200 |
of the given nodes. It is now deprecated and should no longer be |
201 |
used. |
202 |
|
203 |
The ``change-group`` request is used to relocate multiple instances |
204 |
across multiple node groups. ``node-evacuate`` evacuates instances |
205 |
off their node(s). These are described in a separate :ref:`design |
206 |
document <multi-reloc-detailed-design>`. |
207 |
|
208 |
For both allocate and relocate mode, the following extra keys are needed |
209 |
in the ``request`` dictionary: |
210 |
|
211 |
name |
212 |
the name of the instance; if the request is a realocation, then this |
213 |
name will be found in the list of instances (see below), otherwise |
214 |
is the FQDN of the new instance; type *string* |
215 |
|
216 |
required_nodes |
217 |
how many nodes should the algorithm return; while this information |
218 |
can be deduced from the instace's disk template, it's better if |
219 |
this computation is left to Ganeti as then allocator scripts are |
220 |
less sensitive to changes to the disk templates; type *integer* |
221 |
|
222 |
disk_space_total |
223 |
the total disk space that will be used by this instance on the |
224 |
(new) nodes; again, this information can be computed from the list |
225 |
of instance disks and its template type, but Ganeti is better |
226 |
suited to compute it; type *integer* |
227 |
|
228 |
.. pyassert:: |
229 |
|
230 |
constants.DISK_ACCESS_SET == set([constants.DISK_RDONLY, |
231 |
constants.DISK_RDWR]) |
232 |
|
233 |
Allocation needs, in addition: |
234 |
|
235 |
disks |
236 |
list of dictionaries holding the disk definitions for this |
237 |
instance (in the order they are exported to the hypervisor): |
238 |
|
239 |
mode |
240 |
either :pyeval:`constants.DISK_RDONLY` or |
241 |
:pyeval:`constants.DISK_RDWR` denoting if the disk is read-only or |
242 |
writable |
243 |
|
244 |
size |
245 |
the size of this disk in mebibytes |
246 |
|
247 |
nics |
248 |
a list of dictionaries holding the network interfaces for this |
249 |
instance, containing: |
250 |
|
251 |
ip |
252 |
the IP address that Ganeti know for this instance, or null |
253 |
|
254 |
mac |
255 |
the MAC address for this interface |
256 |
|
257 |
bridge |
258 |
the bridge to which this interface will be connected |
259 |
|
260 |
vcpus |
261 |
the number of VCPUs for the instance |
262 |
|
263 |
disk_template |
264 |
the disk template for the instance |
265 |
|
266 |
memory |
267 |
the memory size for the instance |
268 |
|
269 |
os |
270 |
the OS type for the instance |
271 |
|
272 |
tags |
273 |
the list of the instance's tags |
274 |
|
275 |
hypervisor |
276 |
the hypervisor of this instance |
277 |
|
278 |
Relocation: |
279 |
|
280 |
relocate_from |
281 |
a list of nodes to move the instance away from (note that with |
282 |
Ganeti 2.0, this list will always contain a single node, the |
283 |
current secondary of the instance); type *list of strings* |
284 |
|
285 |
As for ``node-evacuate``, it needs the following request arguments: |
286 |
|
287 |
instances |
288 |
a list of instance names to evacuate; type *list of strings* |
289 |
|
290 |
evac_mode |
291 |
specify which instances to evacuate; one of ``primary-only``, |
292 |
``secondary-only``, ``all``, type *string* |
293 |
|
294 |
``change-group`` needs the following request arguments: |
295 |
|
296 |
instances |
297 |
a list of instance names whose group to change; type |
298 |
*list of strings* |
299 |
|
300 |
target_groups |
301 |
must either be the empty list, or contain a list of group UUIDs that |
302 |
should be considered for relocating instances to; type |
303 |
*list of strings* |
304 |
|
305 |
Finally, in the case of multi-evacuate, there's one single request |
306 |
argument (in addition to ``type``): |
307 |
|
308 |
evac_nodes |
309 |
the names of the nodes to be evacuated; type *list of strings* |
310 |
|
311 |
Response message |
312 |
~~~~~~~~~~~~~~~~ |
313 |
|
314 |
The response message is much more simple than the input one. It is |
315 |
also a dict having three keys: |
316 |
|
317 |
success |
318 |
a boolean value denoting if the allocation was successful or not |
319 |
|
320 |
info |
321 |
a string with information from the scripts; if the allocation fails, |
322 |
this will be shown to the user |
323 |
|
324 |
result |
325 |
the output of the algorithm; even if the algorithm failed |
326 |
(i.e. success is false), this must be returned as an empty list |
327 |
|
328 |
for allocate/relocate, this is the list of node(s) for the instance; |
329 |
note that the length of this list must equal the ``requested_nodes`` |
330 |
entry in the input message, otherwise Ganeti will consider the result |
331 |
as failed |
332 |
|
333 |
for multi-relocate mode, this is a list of lists of serialized |
334 |
opcodes; see the :ref:`design document <multi-reloc-result>` for a |
335 |
detailed description |
336 |
|
337 |
for multi-evacuation mode, this is a list of lists; each element of |
338 |
the list is a list of instance name and the new secondary node |
339 |
|
340 |
.. note:: Current Ganeti version accepts either ``result`` or ``nodes`` |
341 |
as a backwards-compatibility measure (older versions only supported |
342 |
``nodes``) |
343 |
|
344 |
Examples |
345 |
-------- |
346 |
|
347 |
Input messages to scripts |
348 |
~~~~~~~~~~~~~~~~~~~~~~~~~ |
349 |
|
350 |
Input message, new instance allocation (common elements are listed this |
351 |
time, but not included in further examples below):: |
352 |
|
353 |
{ |
354 |
"version": 2, |
355 |
"cluster_name": "cluster1.example.com", |
356 |
"cluster_tags": [], |
357 |
"enabled_hypervisors": [ |
358 |
"xen-pvm" |
359 |
], |
360 |
"nodegroups": { |
361 |
"f4e06e0d-528a-4963-a5ad-10f3e114232d": { |
362 |
"name": "default", |
363 |
"alloc_policy": "preferred" |
364 |
} |
365 |
}, |
366 |
"instances": { |
367 |
"instance1.example.com": { |
368 |
"tags": [], |
369 |
"should_run": false, |
370 |
"disks": [ |
371 |
{ |
372 |
"mode": "w", |
373 |
"size": 64 |
374 |
}, |
375 |
{ |
376 |
"mode": "w", |
377 |
"size": 512 |
378 |
} |
379 |
], |
380 |
"nics": [ |
381 |
{ |
382 |
"ip": null, |
383 |
"mac": "aa:00:00:00:60:bf", |
384 |
"bridge": "xen-br0" |
385 |
} |
386 |
], |
387 |
"vcpus": 1, |
388 |
"disk_template": "plain", |
389 |
"memory": 128, |
390 |
"nodes": [ |
391 |
"nodee1.com" |
392 |
], |
393 |
"os": "debootstrap+default" |
394 |
}, |
395 |
"instance2.example.com": { |
396 |
"tags": [], |
397 |
"should_run": false, |
398 |
"disks": [ |
399 |
{ |
400 |
"mode": "w", |
401 |
"size": 512 |
402 |
}, |
403 |
{ |
404 |
"mode": "w", |
405 |
"size": 256 |
406 |
} |
407 |
], |
408 |
"nics": [ |
409 |
{ |
410 |
"ip": null, |
411 |
"mac": "aa:00:00:55:f8:38", |
412 |
"bridge": "xen-br0" |
413 |
} |
414 |
], |
415 |
"vcpus": 1, |
416 |
"disk_template": "drbd", |
417 |
"memory": 512, |
418 |
"nodes": [ |
419 |
"node2.example.com", |
420 |
"node3.example.com" |
421 |
], |
422 |
"os": "debootstrap+default" |
423 |
} |
424 |
}, |
425 |
"nodes": { |
426 |
"node1.example.com": { |
427 |
"total_disk": 858276, |
428 |
"primary_ip": "198.51.100.1", |
429 |
"secondary_ip": "192.0.2.1", |
430 |
"tags": [], |
431 |
"group": "f4e06e0d-528a-4963-a5ad-10f3e114232d", |
432 |
"free_memory": 3505, |
433 |
"free_disk": 856740, |
434 |
"total_memory": 4095 |
435 |
}, |
436 |
"node2.example.com": { |
437 |
"total_disk": 858240, |
438 |
"primary_ip": "198.51.100.2", |
439 |
"secondary_ip": "192.0.2.2", |
440 |
"tags": ["test"], |
441 |
"group": "f4e06e0d-528a-4963-a5ad-10f3e114232d", |
442 |
"free_memory": 3505, |
443 |
"free_disk": 848320, |
444 |
"total_memory": 4095 |
445 |
}, |
446 |
"node3.example.com.com": { |
447 |
"total_disk": 572184, |
448 |
"primary_ip": "198.51.100.3", |
449 |
"secondary_ip": "192.0.2.3", |
450 |
"tags": [], |
451 |
"group": "f4e06e0d-528a-4963-a5ad-10f3e114232d", |
452 |
"free_memory": 3505, |
453 |
"free_disk": 570648, |
454 |
"total_memory": 4095 |
455 |
} |
456 |
}, |
457 |
"request": { |
458 |
"type": "allocate", |
459 |
"name": "instance3.example.com", |
460 |
"required_nodes": 2, |
461 |
"disk_space_total": 3328, |
462 |
"disks": [ |
463 |
{ |
464 |
"mode": "w", |
465 |
"size": 1024 |
466 |
}, |
467 |
{ |
468 |
"mode": "w", |
469 |
"size": 2048 |
470 |
} |
471 |
], |
472 |
"nics": [ |
473 |
{ |
474 |
"ip": null, |
475 |
"mac": "00:11:22:33:44:55", |
476 |
"bridge": null |
477 |
} |
478 |
], |
479 |
"vcpus": 1, |
480 |
"disk_template": "drbd", |
481 |
"memory": 2048, |
482 |
"os": "debootstrap+default", |
483 |
"tags": [ |
484 |
"type:test", |
485 |
"owner:foo" |
486 |
], |
487 |
hypervisor: "xen-pvm" |
488 |
} |
489 |
} |
490 |
|
491 |
Input message, reallocation:: |
492 |
|
493 |
{ |
494 |
"version": 2, |
495 |
... |
496 |
"request": { |
497 |
"type": "relocate", |
498 |
"name": "instance2.example.com", |
499 |
"required_nodes": 1, |
500 |
"disk_space_total": 832, |
501 |
"relocate_from": [ |
502 |
"node3.example.com" |
503 |
] |
504 |
} |
505 |
} |
506 |
|
507 |
Input message, node evacuation:: |
508 |
|
509 |
{ |
510 |
"version": 2, |
511 |
... |
512 |
"request": { |
513 |
"type": "multi-evacuate", |
514 |
"evac_nodes": [ |
515 |
"node2" |
516 |
], |
517 |
} |
518 |
} |
519 |
|
520 |
|
521 |
Response messages |
522 |
~~~~~~~~~~~~~~~~~ |
523 |
Successful response message:: |
524 |
|
525 |
{ |
526 |
"success": true, |
527 |
"info": "Allocation successful", |
528 |
"result": [ |
529 |
"node2.example.com", |
530 |
"node1.example.com" |
531 |
] |
532 |
} |
533 |
|
534 |
Failed response message:: |
535 |
|
536 |
{ |
537 |
"success": false, |
538 |
"info": "Can't find a suitable node for position 2 (already selected: node2.example.com)", |
539 |
"result": [] |
540 |
} |
541 |
|
542 |
Successful node evacuation message:: |
543 |
|
544 |
{ |
545 |
"success": true, |
546 |
"info": "Request successful", |
547 |
"result": [ |
548 |
[ |
549 |
"instance1", |
550 |
"node3" |
551 |
], |
552 |
[ |
553 |
"instance2", |
554 |
"node1" |
555 |
] |
556 |
] |
557 |
} |
558 |
|
559 |
|
560 |
Command line messages |
561 |
~~~~~~~~~~~~~~~~~~~~~ |
562 |
:: |
563 |
|
564 |
# gnt-instance add -t plain -m 2g --os-size 1g --swap-size 512m --iallocator hail -o debootstrap+default instance3 |
565 |
Selected nodes for the instance: node1.example.com |
566 |
* creating instance disks... |
567 |
[...] |
568 |
|
569 |
# gnt-instance add -t plain -m 3400m --os-size 1g --swap-size 512m --iallocator hail -o debootstrap+default instance4 |
570 |
Failure: prerequisites not met for this operation: |
571 |
Can't compute nodes using iallocator 'hail': Can't find a suitable node for position 1 (already selected: ) |
572 |
|
573 |
# gnt-instance add -t drbd -m 1400m --os-size 1g --swap-size 512m --iallocator hail -o debootstrap+default instance5 |
574 |
Failure: prerequisites not met for this operation: |
575 |
Can't compute nodes using iallocator 'hail': Can't find a suitable node for position 2 (already selected: node1.example.com) |
576 |
|
577 |
Reference implementation |
578 |
~~~~~~~~~~~~~~~~~~~~~~~~ |
579 |
|
580 |
Ganeti's default iallocator is "hail" which is available when "htools" |
581 |
components have been enabled at build time (see :doc:`install-quick` for |
582 |
more details). |
583 |
|
584 |
.. vim: set textwidth=72 : |
585 |
.. Local Variables: |
586 |
.. mode: rst |
587 |
.. fill-column: 72 |
588 |
.. End: |