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 cluster.
174 If the bitwise OR of all the ``status`` fields is 0, the cluster is
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, with at least the following fields for each instance:
252 The name of the instance.
255 The UUID of the instance (stable on name change).
258 The status of the instance (up/down/offline) as requested by the admin.
261 The actual status of the instance. It can be ``up``, ``down``, or
262 ``hung`` if the instance is up but it appears to be completely stuck.
265 The uptime of the instance (if it is up, "null" otherwise).
268 The timestamp of the last known change to the instance state.
271 The last known reason for state change of the instance, described according
272 to the JSON representation of a reason trail, as detailed in the :doc:`reason trail
273 design document <design-reason-trail>`.
276 It represents the status of the instance, and its format is the same as that
277 of the ``status`` field of `Status reporting collectors`_.
279 Each hypervisor should provide its own instance status data collector, possibly
280 with the addition of more, specific, fields.
281 The ``category`` field of all of them will be ``instance``.
282 The ``kind`` field will be ``1``.
284 Note that as soon as a node knows it's not the primary anymore for an
285 instance it will stop reporting status for it: this means the instance
286 will either disappear, if it has been deleted, or appear on another
287 node, if it's been moved.
289 The ``code`` of the ``status`` field of the report of the Instance status data
293 if ``status`` is ``0`` for all the instances it is reporting about.
301 The storage status collectors will be a series of data collectors
302 (drbd, rbd, plain, file) that will gather data about all the storage types
303 for the current node (this is right now hardcoded to the enabled storage
304 types, and in the future tied to the enabled storage pools for the nodegroup).
306 The ``name`` of each of these collector will reflect what storage type each of
309 The ``category`` field of these collector will be ``storage``.
311 The ``kind`` field will be ``1`` (`Status reporting collectors`_).
313 The ``data`` section of the report will provide at least the following fields:
316 The amount of free space (in KBytes).
319 The amount of used space (in KBytes).
322 The total visible space (in KBytes).
324 Each specific storage type might provide more type-specific fields.
326 In case of error, the ``message`` subfield of the ``status`` field of the
327 report of the instance status collector will disclose the nature of the error
328 as a type specific information. Examples of these are "backend pv unavailable"
329 for lvm storage, "unreachable" for network based storage or "filesystem error"
330 for filesystem based implementations.
335 This data collector will run only on nodes where DRBD is actually
336 present and it will gather information about DRBD devices.
338 Its ``kind`` in the report will be ``1`` (`Status reporting collectors`_).
340 Its ``category`` field in the report will contain the value ``storage``.
342 When executed in verbose mode, the ``data`` section of the report of this
343 collector will provide the following fields:
346 Information about the DRBD version number, given by a combination of
347 any (but at least one) of the following fields:
350 The DRBD driver version.
353 The API version number.
356 The protocol version.
359 The version of the source files.
362 Git hash of the source files.
365 Who built the binary, and, optionally, when.
368 A list of structures, each describing a DRBD device (a minor) and containing
369 the following fields:
372 The device minor number.
375 The state of the connection. If it is "Unconfigured", all the following
376 fields are not present.
379 The role of the local resource.
382 The role of the remote resource.
385 The status of the local disk.
388 The status of the remote disk.
390 ``replicationProtocol``
391 The replication protocol being used.
394 The input/output flags.
397 The performance indicators. This field will contain the following
401 KiB of data sent on the network.
404 KiB of data received from the network.
407 KiB of data written on local disk.
410 KiB of date read from the local disk.
413 Number of updates of the activity log.
416 Number of updates to the bitmap area of the metadata.
419 Number of open requests to the local I/O subsystem.
422 Number of requests sent to the partner but not yet answered.
425 Number of requests received by the partner but still to be answered.
427 ``applicationPending``
428 Num of block input/output requests forwarded to DRBD but that have not yet
432 (Optional) Number of epoch objects. Not provided by all DRBD versions.
435 (Optional) Currently used write ordering method. Not provided by all DRBD
439 (Optional) KiB of storage currently out of sync. Not provided by all DRBD
443 (Optional) The status of the synchronization of the disk. This is present
444 only if the disk is being synchronized, and includes the following fields:
447 The percentage of synchronized data.
450 How far the synchronization is. Written as "x/y", where x and y are
451 integer numbers expressed in the measurement unit stated in
455 The measurement unit for the progress indicator.
458 The expected time before finishing the synchronization.
461 The speed of the synchronization.
464 The desiderd speed of the synchronization.
467 The measurement unit of the ``speed`` and ``want`` values. Expressed
471 The name of the Ganeti instance this disk is associated to.
474 Ganeti daemons status
475 +++++++++++++++++++++
477 Ganeti will report what information it has about its own daemons.
478 This should allow identifying possible problems with the Ganeti system itself:
479 for example memory leaks, crashes and high resource utilization should be
480 evident by analyzing this information.
482 The ``kind`` field will be ``1`` (`Status reporting collectors`_).
484 Each daemon will have its own data collector, and each of them will have
485 a ``category`` field valued ``daemon``.
487 When executed in verbose mode, their data section will include at least:
490 The amount of used memory.
493 The measurement unit used for the memory.
496 The uptime of the daemon.
499 How much cpu the daemon is using (percentage).
501 Any other daemon-specific information can be included as well in the ``data``
504 Hypervisor resources report
505 +++++++++++++++++++++++++++
507 Each hypervisor has a view of system resources that sometimes is
508 different than the one the OS sees (for example in Xen the Node OS,
509 running as Dom0, has access to only part of those resources). In this
510 section we'll report all information we can in a "non hypervisor
511 specific" way. Each hypervisor can then add extra specific information
512 that is not generic enough be abstracted.
514 The ``kind`` field will be ``0`` (`Performance reporting collectors`_).
516 Each of the hypervisor data collectory will be of ``category``: ``hypervisor``.
518 Node OS resources report
519 ++++++++++++++++++++++++
521 Since Ganeti assumes it's running on Linux, it's useful to export some
522 basic information as seen by the host system.
524 The ``category`` field of the report will be ``null``.
526 The ``kind`` field will be ``0`` (`Performance reporting collectors`_).
528 The ``data`` section will include:
531 The number of available cpus.
534 A list with one element per cpu, showing its average load.
537 The current view of memory (free, used, cached, etc.)
540 A list with one element per filesystem, showing a summary of the
541 total/available space.
544 A list with one element per network interface, showing the amount of
545 sent/received data, error rate, IP address of the interface, etc.
548 A map using the name of a component Ganeti interacts (Linux, drbd,
549 hypervisor, etc) as the key and its version number as the value.
551 Note that we won't go into any hardware specific details (e.g. querying a
552 node RAID is outside the scope of this, and can be implemented as a
553 plugin) but we can easily just report the information above, since it's
554 standard enough across all systems.
559 .. include:: monitoring-query-format.rst
561 Instance disk status propagation
562 --------------------------------
564 As for the instance status Ganeti has now only partial information about
565 its instance disks: in particular each node is unaware of the disk to
566 instance mapping, that exists only on the master.
568 For this design doc we plan to fix this by changing all RPCs that create
569 a backend storage or that put an already existing one in use and passing
570 the relevant instance to the node. The node can then export these to the
571 status reporting tool.
573 While we haven't implemented these RPC changes yet, we'll use Confd to
574 fetch this information in the data collectors.
579 The monitoring system will be equipped with a plugin system that can
580 export specific local information through it.
582 The plugin system is expected to be used by local installations to
583 export any installation specific information that they want to be
584 monitored, about either hardware or software on their systems.
586 The plugin system will be in the form of either scripts or binaries whose output
587 will be inserted in the report.
589 Eventually support for other kinds of plugins might be added as well, such as
590 plain text files which will be inserted into the report, or local unix or
591 network sockets from which the information has to be read. This should allow
592 most flexibility for implementing an efficient system, while being able to keep
593 it as simple as possible.
598 In order to ease testing as well as to make it simple to reuse this
599 subsystem it will be possible to run just the "data collectors" on each
600 node without passing through the agent daemon.
602 If a data collector is run independently, it should print on stdout its
603 report, according to the format corresponding to a single data collector
604 report object, as described in the previous paragraphs.
609 In order to be able to report information fast the monitoring agent
610 daemon will keep an in-memory or on-disk cache of the status, which will
611 be returned when queries are made. The status system will then
612 periodically check resources to make sure the status is up to date.
614 Different parts of the report will be queried at different speeds. These
616 - how often they vary (or we expect them to vary)
617 - how fast they are to query
618 - how important their freshness is
620 Of course the last parameter is installation specific, and while we'll
621 try to have defaults, it will be configurable. The first two instead we
622 can use adaptively to query a certain resource faster or slower
623 depending on those two parameters.
625 When run as stand-alone binaries, the data collector will not using any
626 caching system, and just fetch and return the data immediately.
631 The status daemon will be implemented as a standalone Haskell daemon. In
632 the future it should be easy to merge multiple daemons into one with
633 multiple entry points, should we find out it saves resources and doesn't
634 impact functionality.
636 The libekg library should be looked at for easily providing metrics in
642 We will implement the agent system in this order:
644 - initial example data collectors (eg. for drbd and instance status).
645 - initial daemon for exporting data, integrating the existing collectors
647 - RPC updates for instance status reasons and disk to instance mapping
648 - cache layer for the daemon
649 - more data collectors
655 As a future step it can be useful to "centralize" all this reporting
656 data on a single place. This for example can be just the master node, or
657 all the master candidates. We will evaluate doing this after the first
658 node-local version has been developed and tested.
660 Another possible change is replacing the "read-only" RPCs with queries
661 to the agent system, thus having only one way of collecting information
662 from the nodes from a monitoring system and for Ganeti itself.
664 One extra feature we may need is a way to query for only sub-parts of
665 the report (eg. instances status only). This can be done by passing
666 arguments to the HTTP GET, which will be defined when we get to this
669 Finally the :doc:`autorepair system design <design-autorepair>`. system
670 (see its design) can be expanded to use the monitoring agent system as a
671 source of information to decide which repairs it can perform.
673 .. vim: set textwidth=72 :