1 =======================
2 Ganeti monitoring agent
3 =======================
5 .. contents:: :depth: 4
7 This is a design document detailing the implementation of a Ganeti
8 monitoring agent report system, that can be queried by a monitoring
9 system to calculate health information for a Ganeti cluster.
11 Current state and shortcomings
12 ==============================
14 There is currently no monitoring support in Ganeti. While we don't want
15 to build something like Nagios or Pacemaker as part of Ganeti, it would
16 be useful if such tools could easily extract information from a Ganeti
17 machine in order to take actions (example actions include logging an
18 outage for future reporting or alerting a person or system about it).
23 Each Ganeti node should export a status page that can be queried by a
24 monitoring system. Such status page will be exported on a network port
25 and will be encoded in JSON (simple text) over HTTP.
27 The choice of JSON is obvious as we already depend on it in Ganeti and
28 thus we don't need to add extra libraries to use it, as opposed to what
29 would happen for XML or some other markup format.
31 Location of agent report
32 ------------------------
34 The report will be available from all nodes, and be concerned for all
35 node-local resources. This allows more real-time information to be
36 available, at the cost of querying all nodes.
41 The monitoring agent system will report on the following basic information:
44 - Instance disk status
45 - Status of storage for instances
46 - Ganeti daemons status, CPU usage, memory footprint
47 - Hypervisor resources report (memory, CPU, network interfaces)
48 - Node OS resources report (memory, CPU, network interfaces)
49 - Information from a plugin system
54 The report of the will be in JSON format, and it will present an array
56 Each report object will be produced by a specific data collector.
57 Each report object includes some mandatory fields, to be provided by all
61 The name of the data collector that produced this part of the report.
62 It is supposed to be unique inside a report.
65 The version of the data collector that produces this part of the
66 report. Built-in data collectors (as opposed to those implemented as
67 plugins) should have "B" as the version number.
70 The format of what is represented in the "data" field for each data
71 collector might change over time. Every time this happens, the
72 format_version should be changed, so that who reads the report knows
73 what format to expect, and how to correctly interpret it.
76 The time when the reported data were gathered. It has to be expressed
77 in nanoseconds since the unix epoch (0:00:00 January 01, 1970). If not
78 enough precision is available (or needed) it can be padded with
79 zeroes. If a report object needs multiple timestamps, it can add more
80 and/or override this one inside its own "data" section.
83 A collector can belong to a given category of collectors (e.g.: storage
84 collectors, daemon collector). This means that it will have to provide a
85 minumum set of prescribed fields, as documented for each category.
86 This field will contain the name of the category the collector belongs to,
87 if any, or just the ``null`` value.
90 Two kinds of collectors are possible:
91 `Performance reporting collectors`_ and `Status reporting collectors`_.
92 The respective paragraphs will describe them and the value of this field.
95 This field contains all the data generated by the specific data collector,
96 in its own independently defined format. The monitoring agent could check
97 this syntactically (according to the JSON specifications) but not
100 Here follows a minimal example of a report::
104 "name" : "TheCollectorIdentifier",
106 "format_version" : 1,
107 "timestamp" : 1351607182000000000,
110 "data" : { "plugin_specific_data" : "go_here" }
113 "name" : "AnotherDataCollector",
115 "format_version" : 7,
116 "timestamp" : 1351609526123854000,
117 "category" : "storage",
119 "data" : { "status" : { "code" : 1,
120 "message" : "Error on disk 2"
122 "plugin_specific" : "data",
123 "some_late_data" : { "timestamp" : 1351609526123942720,
130 Performance reporting collectors
131 ++++++++++++++++++++++++++++++++
133 These collectors only provide data about some component of the system, without
134 giving any interpretation over their meaning.
136 The value of the ``kind`` field of the report will be ``0``.
138 Status reporting collectors
139 +++++++++++++++++++++++++++
141 These collectors will provide information about the status of some
142 component of ganeti, or managed by ganeti.
144 The value of their ``kind`` field will be ``1``.
146 The rationale behind this kind of collectors is that there are some situations
147 where exporting data about the underlying subsystems would expose potential
148 issues. But if Ganeti itself is able (and going) to fix the problem, conflicts
149 might arise between Ganeti and something/somebody else trying to fix the same
151 Also, some external monitoring systems might not be aware of the internals of a
152 particular subsystem (e.g.: DRBD) and might only exploit the high level
153 response of its data collector, alerting an administrator if anything is wrong.
154 Still, completely hiding the underlying data is not a good idea, as they might
155 still be of use in some cases. So status reporting plugins will provide two
156 output modes: one just exporting a high level information about the status,
157 and one also exporting all the data they gathered.
158 The default output mode will be the status-only one. Through a command line
159 parameter (for stand-alone data collectors) or through the HTTP request to the
161 (when collectors are executed as part of it) the verbose output mode providing
162 all the data can be selected.
164 When exporting just the status each status reporting collector will provide,
165 in its ``data`` section, at least the following field:
168 summarizes the status of the component being monitored and consists of two
172 It assumes a numeric value, encoded in such a way to allow using a bitset
173 to easily distinguish which states are currently present in the whole
174 cluster. If the bitwise OR of all the ``status`` fields is 0, the cluster
175 is completely healty.
176 The status codes are as follows:
179 The collector can determine that everything is working as
183 Something is temporarily wrong but it is being automatically fixed by
185 There is no need of external intervention.
188 The collector has failed to understand whether the status is good or
189 bad. Further analysis is required. Interpret this status as a
190 potentially dangerous situation.
193 The collector can determine that something is wrong and Ganeti has no
194 way to fix it autonomously. External intervention is required.
197 A message to better explain the reason of the status.
198 The exact format of the message string is data collector dependent.
200 The field is mandatory, but the content can be an empty string if the
201 ``code`` is ``0`` (working as intended) or ``1`` (being fixed
204 If the status code is ``2``, the message should specify what has gone
206 If the status code is ``4``, the message shoud explain why it was not
207 possible to determine a proper status.
209 The ``data`` section will also contain all the fields describing the gathered
210 data, according to a collector-specific format.
215 At the moment each node knows which instances are running on it, which
216 instances it is primary for, but not the cause why an instance might not
217 be running. On the other hand we don't want to distribute full instance
218 "admin" status information to all nodes, because of the performance
219 impact this would have.
221 As such we propose that:
223 - Any operation that can affect instance status will have an optional
224 "reason" attached to it (at opcode level). This can be used for
225 example to distinguish an admin request, from a scheduled maintenance
226 or an automated tool's work. If this reason is not passed, Ganeti will
227 just use the information it has about the source of the request.
228 This reason information will be structured according to the
229 :doc:`Ganeti reason trail <design-reason-trail>` design document.
230 - RPCs that affect the instance status will be changed so that the
231 "reason" and the version of the config object they ran on is passed to
232 them. They will then export the new expected instance status, together
233 with the associated reason and object version to the status report
234 system, which then will export those themselves.
236 Monitoring and auditing systems can then use the reason to understand
237 the cause of an instance status, and they can use the timestamp to
238 understand the freshness of their data even in the absence of an atomic
239 cross-node reporting: for example if they see an instance "up" on a node
240 after seeing it running on a previous one, they can compare these values
241 to understand which data is freshest, and repoll the "older" node. Of
242 course if they keep seeing this status this represents an error (either
243 an instance continuously "flapping" between nodes, or an instance is
244 constantly up on more than one), which should be reported and acted
247 The instance status will be on each node, for the instances it is
248 primary for, and its ``data`` section of the report will contain a list
249 of instances, named ``instances``, with at least the following fields for
253 The name of the instance.
256 The UUID of the instance (stable on name change).
259 The status of the instance (up/down/offline) as requested by the admin.
262 The actual status of the instance. It can be ``up``, ``down``, or
263 ``hung`` if the instance is up but it appears to be completely stuck.
266 The uptime of the instance (if it is up, "null" otherwise).
269 The timestamp of the last known change to the instance state.
272 The last known reason for state change of the instance, described according
273 to the JSON representation of a reason trail, as detailed in the :doc:`reason
274 trail design document <design-reason-trail>`.
277 It represents the status of the instance, and its format is the same as that
278 of the ``status`` field of `Status reporting collectors`_.
280 Each hypervisor should provide its own instance status data collector, possibly
281 with the addition of more, specific, fields.
282 The ``category`` field of all of them will be ``instance``.
283 The ``kind`` field will be ``1``.
285 Note that as soon as a node knows it's not the primary anymore for an
286 instance it will stop reporting status for it: this means the instance
287 will either disappear, if it has been deleted, or appear on another
288 node, if it's been moved.
290 The ``code`` of the ``status`` field of the report of the Instance status data
294 if ``status`` is ``0`` for all the instances it is reporting about.
302 The storage collectors will be a series of data collectors
303 that will gather data about storage for the current node. The collection
304 will be performed at different granularity and abstraction levels, from
305 the physical disks, to partitions, logical volumes and to the specific
306 storage types used by Ganeti itself (drbd, rbd, plain, file).
308 The ``name`` of each of these collector will reflect what storage type each of
311 The ``category`` field of these collector will be ``storage``.
313 The ``kind`` field will depend on the specific collector.
315 Each ``storage`` collector's ``data`` section will provide collector-specific
318 The various storage collectors will provide keys to join the data they provide,
319 in order to allow the user to get a better understanding of the system. E.g.:
320 through device names, or instance names.
325 This storage data collector will gather information about the status of the
326 disks installed in the system, as listed in the /proc/diskstats file. This means
327 that not only physical hard drives, but also ramdisks and loopback devices will
330 Its ``kind`` in the report will be ``0`` (`Performance reporting collectors`_).
332 Its ``category`` field in the report will contain the value ``storage``.
334 When executed in verbose mode, the ``data`` section of the report of this
335 collector will be a list of items, each representing one disk, each providing
336 the following fields:
339 The major number of the device.
342 The minor number of the device.
345 The name of the device.
348 This is the total number of reads completed successfully.
351 Reads which are adjacent to each other may be merged for efficiency. Thus
352 two 4K reads may become one 8K read before it is ultimately handed to the
353 disk, and so it will be counted (and queued) as only one I/O. This field
354 specifies how often this was done.
357 This is the total number of sectors read successfully.
360 This is the total number of milliseconds spent by all reads.
363 This is the total number of writes completed successfully.
366 Writes which are adjacent to each other may be merged for efficiency. Thus
367 two 4K writes may become one 8K read before it is ultimately handed to the
368 disk, and so it will be counted (and queued) as only one I/O. This field
369 specifies how often this was done.
372 This is the total number of sectors written successfully.
375 This is the total number of milliseconds spent by all writes.
378 The number of I/Os currently in progress.
379 The only field that should go to zero, it is incremented as requests are
380 given to appropriate struct request_queue and decremented as they finish.
383 The number of milliseconds spent doing I/Os. This field increases so long
384 as field ``IOs`` is nonzero.
387 The weighted number of milliseconds spent doing I/Os.
388 This field is incremented at each I/O start, I/O completion, I/O merge,
389 or read of these stats by the number of I/Os in progress (field ``IOs``)
390 times the number of milliseconds spent doing I/O since the last update of
391 this field. This can provide an easy measure of both I/O completion time
392 and the backlog that may be accumulating.
394 Logical Volume collector
395 ************************
397 This data collector will gather information about the attributes of logical
398 volumes present in the system.
400 Its ``kind`` in the report will be ``0`` (`Performance reporting collectors`_).
402 Its ``category`` field in the report will contain the value ``storage``.
404 The ``data`` section of the report of this collector will be a list of items,
405 each representing one logical volume and providing the following fields:
408 The UUID of the logical volume.
411 The name of the logical volume.
414 The attributes of the logical volume.
417 Persistent major number or -1 if not persistent.
420 Persistent minor number or -1 if not persistent.
423 Currently assigned major number or -1 if LV is not active.
426 Currently assigned minor number or -1 if LV is not active.
432 Number of segments in LV.
438 Kernel device-mapper modules required for this LV, if any.
441 Unique identifier of the volume group.
444 Name of the volume group.
450 Offset within the LVto the start of the segment in bytes.
453 Offset within the LV to the start of the segment in physical extents.
456 Size of the segment in bytes.
459 Tags for the segment, if any.
462 Ranges of Physical Extents of underlying devices in lvs command line format.
465 Underlying devices used with starting extent numbers.
468 The name of the instance this LV is used by.
473 This data collector will run only on nodes where DRBD is actually
474 present and it will gather information about DRBD devices.
476 Its ``kind`` in the report will be ``1`` (`Status reporting collectors`_).
478 Its ``category`` field in the report will contain the value ``storage``.
480 When executed in verbose mode, the ``data`` section of the report of this
481 collector will provide the following fields:
484 Information about the DRBD version number, given by a combination of
485 any (but at least one) of the following fields:
488 The DRBD driver version.
491 The API version number.
494 The protocol version.
497 The version of the source files.
500 Git hash of the source files.
503 Who built the binary, and, optionally, when.
506 A list of structures, each describing a DRBD device (a minor) and containing
507 the following fields:
510 The device minor number.
513 The state of the connection. If it is "Unconfigured", all the following
514 fields are not present.
517 The role of the local resource.
520 The role of the remote resource.
523 The status of the local disk.
526 The status of the remote disk.
528 ``replicationProtocol``
529 The replication protocol being used.
532 The input/output flags.
535 The performance indicators. This field will contain the following
539 KiB of data sent on the network.
542 KiB of data received from the network.
545 KiB of data written on local disk.
548 KiB of date read from the local disk.
551 Number of updates of the activity log.
554 Number of updates to the bitmap area of the metadata.
557 Number of open requests to the local I/O subsystem.
560 Number of requests sent to the partner but not yet answered.
563 Number of requests received by the partner but still to be answered.
565 ``applicationPending``
566 Num of block input/output requests forwarded to DRBD but that have not yet
570 (Optional) Number of epoch objects. Not provided by all DRBD versions.
573 (Optional) Currently used write ordering method. Not provided by all DRBD
577 (Optional) KiB of storage currently out of sync. Not provided by all DRBD
581 (Optional) The status of the synchronization of the disk. This is present
582 only if the disk is being synchronized, and includes the following fields:
585 The percentage of synchronized data.
588 How far the synchronization is. Written as "x/y", where x and y are
589 integer numbers expressed in the measurement unit stated in
593 The measurement unit for the progress indicator.
596 The expected time before finishing the synchronization.
599 The speed of the synchronization.
602 The desiderd speed of the synchronization.
605 The measurement unit of the ``speed`` and ``want`` values. Expressed
609 The name of the Ganeti instance this disk is associated to.
612 Ganeti daemons status
613 +++++++++++++++++++++
615 Ganeti will report what information it has about its own daemons.
616 This should allow identifying possible problems with the Ganeti system itself:
617 for example memory leaks, crashes and high resource utilization should be
618 evident by analyzing this information.
620 The ``kind`` field will be ``1`` (`Status reporting collectors`_).
622 Each daemon will have its own data collector, and each of them will have
623 a ``category`` field valued ``daemon``.
625 When executed in verbose mode, their data section will include at least:
628 The amount of used memory.
631 The measurement unit used for the memory.
634 The uptime of the daemon.
637 How much cpu the daemon is using (percentage).
639 Any other daemon-specific information can be included as well in the ``data``
642 Hypervisor resources report
643 +++++++++++++++++++++++++++
645 Each hypervisor has a view of system resources that sometimes is
646 different than the one the OS sees (for example in Xen the Node OS,
647 running as Dom0, has access to only part of those resources). In this
648 section we'll report all information we can in a "non hypervisor
649 specific" way. Each hypervisor can then add extra specific information
650 that is not generic enough be abstracted.
652 The ``kind`` field will be ``0`` (`Performance reporting collectors`_).
654 Each of the hypervisor data collectory will be of ``category``: ``hypervisor``.
656 Node OS resources report
657 ++++++++++++++++++++++++
659 Since Ganeti assumes it's running on Linux, it's useful to export some
660 basic information as seen by the host system.
662 The ``category`` field of the report will be ``null``.
664 The ``kind`` field will be ``0`` (`Performance reporting collectors`_).
666 The ``data`` section will include:
669 The number of available cpus.
672 A list with one element per cpu, showing its average load.
675 The current view of memory (free, used, cached, etc.)
678 A list with one element per filesystem, showing a summary of the
679 total/available space.
682 A list with one element per network interface, showing the amount of
683 sent/received data, error rate, IP address of the interface, etc.
686 A map using the name of a component Ganeti interacts (Linux, drbd,
687 hypervisor, etc) as the key and its version number as the value.
689 Note that we won't go into any hardware specific details (e.g. querying a
690 node RAID is outside the scope of this, and can be implemented as a
691 plugin) but we can easily just report the information above, since it's
692 standard enough across all systems.
697 .. include:: monitoring-query-format.rst
699 Instance disk status propagation
700 --------------------------------
702 As for the instance status Ganeti has now only partial information about
703 its instance disks: in particular each node is unaware of the disk to
704 instance mapping, that exists only on the master.
706 For this design doc we plan to fix this by changing all RPCs that create
707 a backend storage or that put an already existing one in use and passing
708 the relevant instance to the node. The node can then export these to the
709 status reporting tool.
711 While we haven't implemented these RPC changes yet, we'll use Confd to
712 fetch this information in the data collectors.
717 The monitoring system will be equipped with a plugin system that can
718 export specific local information through it.
720 The plugin system is expected to be used by local installations to
721 export any installation specific information that they want to be
722 monitored, about either hardware or software on their systems.
724 The plugin system will be in the form of either scripts or binaries whose output
725 will be inserted in the report.
727 Eventually support for other kinds of plugins might be added as well, such as
728 plain text files which will be inserted into the report, or local unix or
729 network sockets from which the information has to be read. This should allow
730 most flexibility for implementing an efficient system, while being able to keep
731 it as simple as possible.
736 In order to ease testing as well as to make it simple to reuse this
737 subsystem it will be possible to run just the "data collectors" on each
738 node without passing through the agent daemon.
740 If a data collector is run independently, it should print on stdout its
741 report, according to the format corresponding to a single data collector
742 report object, as described in the previous paragraphs.
747 In order to be able to report information fast the monitoring agent
748 daemon will keep an in-memory or on-disk cache of the status, which will
749 be returned when queries are made. The status system will then
750 periodically check resources to make sure the status is up to date.
752 Different parts of the report will be queried at different speeds. These
754 - how often they vary (or we expect them to vary)
755 - how fast they are to query
756 - how important their freshness is
758 Of course the last parameter is installation specific, and while we'll
759 try to have defaults, it will be configurable. The first two instead we
760 can use adaptively to query a certain resource faster or slower
761 depending on those two parameters.
763 When run as stand-alone binaries, the data collector will not using any
764 caching system, and just fetch and return the data immediately.
769 The status daemon will be implemented as a standalone Haskell daemon. In
770 the future it should be easy to merge multiple daemons into one with
771 multiple entry points, should we find out it saves resources and doesn't
772 impact functionality.
774 The libekg library should be looked at for easily providing metrics in
780 We will implement the agent system in this order:
782 - initial example data collectors (eg. for drbd and instance status).
783 - initial daemon for exporting data, integrating the existing collectors
785 - RPC updates for instance status reasons and disk to instance mapping
786 - cache layer for the daemon
787 - more data collectors
793 As a future step it can be useful to "centralize" all this reporting
794 data on a single place. This for example can be just the master node, or
795 all the master candidates. We will evaluate doing this after the first
796 node-local version has been developed and tested.
798 Another possible change is replacing the "read-only" RPCs with queries
799 to the agent system, thus having only one way of collecting information
800 from the nodes from a monitoring system and for Ganeti itself.
802 One extra feature we may need is a way to query for only sub-parts of
803 the report (eg. instances status only). This can be done by passing
804 arguments to the HTTP GET, which will be defined when we get to this
807 Finally the :doc:`autorepair system design <design-autorepair>`. system
808 (see its design) can be expanded to use the monitoring agent system as a
809 source of information to decide which repairs it can perform.
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