Synnefo » snf-ganeti

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Ganeti monitoring agent

=======================

.. contents:: :depth: 4

This is a design document detailing the implementation of a Ganeti

monitoring agent report system, that can be queried by a monitoring

system to calculate health information for a Ganeti cluster.

Current state and shortcomings

==============================

There is currently no monitoring support in Ganeti. While we don't want

to build something like Nagios or Pacemaker as part of Ganeti, it would

be useful if such tools could easily extract information from a Ganeti

machine in order to take actions (example actions include logging an

outage for future reporting or alerting a person or system about it).

Proposed changes

================

Each Ganeti node should export a status page that can be queried by a

monitoring system. Such status page will be exported on a network port

and will be encoded in JSON (simple text) over HTTP.

The choice of JSON is obvious as we already depend on it in Ganeti and

thus we don't need to add extra libraries to use it, as opposed to what

would happen for XML or some other markup format.

Location of agent report

------------------------

The report will be available from all nodes, and be concerned for all

node-local resources. This allows more real-time information to be

available, at the cost of querying all nodes.

Information reported

--------------------

The monitoring agent system will report on the following basic information:

- Instance status

- Instance disk status

- Status of storage for instances

- Ganeti daemons status, CPU usage, memory footprint

- Hypervisor resources report (memory, CPU, network interfaces)

- Node OS resources report (memory, CPU, network interfaces)

- Information from a plugin system

Format of the query

-------------------

The query will be an HTTP GET request on a particular port. At the

beginning it will only be possible to query the full status report.

Format of the report

--------------------

The report of the will be in JSON format, and it will present an array

of report objects.

Each report object will be produced by a specific data collector.

Each report object includes some mandatory fields, to be provided by all

the data collectors:

``name``

  The name of the data collector that produced this part of the report.

  It is supposed to be unique inside a report.

``version``

  The version of the data collector that produces this part of the

  report. Built-in data collectors (as opposed to those implemented as

  plugins) should have "B" as the version number.

``formatVersion``

  The format of what is represented in the "data" field for each data

  collector might change over time. Every time this happens, the

  format_version should be changed, so that who reads the report knows

  what format to expect, and how to correctly interpret it.

``timestamp``

  The time when the reported data were gathered. Is has to be expressed

  in nanoseconds since the unix epoch (0:00:00 January 01, 1970). If not

  enough precision is available (or needed) it can be padded with

  zeroes. If a report object needs multiple timestamps, it can add more

  and/or override this one inside its own "data" section.

``category``

  A collector can belong to a given category of collectors (e.g.: storage

  collectors, daemon collector). This means that it will have to provide a

  minumum set of prescribed fields, as documented for each category.

  This field will contain the name of the category the collector belongs to,

  if any, or just the ``null`` value.

``kind``

  Two kinds of collectors are possible:

  `Performance reporting collectors`_ and `Status reporting collectors`_.

  The respective paragraphs will describe them and the value of this field.

``data``

  This field contains all the data generated by the specific data collector,

  in its own independently defined format. The monitoring agent could check

  this syntactically (according to the JSON specifications) but not

  semantically.

Here follows a minimal example of a report::

  [

  {

      "name" : "TheCollectorIdentifier",

      "version" : "1.2",

      "formatVersion" : 1,

      "timestamp" : 1351607182000000000,

      "category" : null,

      "kind" : 0,

      "data" : { "plugin_specific_data" : "go_here" }

  },

  {

      "name" : "AnotherDataCollector",

      "version" : "B",

      "formatVersion" : 7,

      "timestamp" : 1351609526123854000,

      "category" : "storage",

      "kind" : 1,

      "data" : { "status" : { "code" : 1,

                              "message" : "Error on disk 2"

                            },

                 "plugin_specific" : "data",

                 "some_late_data" : { "timestamp" : 1351609526123942720,

                                      ...

                                    }

               }

  }

  ]

Performance reporting collectors

++++++++++++++++++++++++++++++++

These collectors only provide data about some component of the system, without

giving any interpretation over their meaning.

The value of the ``kind`` field of the report will be ``0``.

Status reporting collectors

+++++++++++++++++++++++++++

These collectors will provide information about the status of some

component of ganeti, or managed by ganeti.

The value of their ``kind`` field will be ``1``.

The rationale behind this kind of collectors is that there are some situations

where exporting data about the underlying subsystems would expose potential

issues. But if Ganeti itself is able (and going) to fix the problem, conflicts

might arise between Ganeti and something/somebody else trying to fix the same

problem.

Also, some external monitoring systems might not be aware of the internals of a

particular subsystem (e.g.: DRBD) and might only exploit the high level

response of its data collector, alerting an administrator if anything is wrong.

Still, completely hiding the underlying data is not a good idea, as they might

still be of use in some cases. So status reporting plugins will provide two

output modes: one just exporting a high level information about the status,

and one also exporting all the data they gathered.

The default output mode will be the status-only one. Through a command line

parameter (for stand-alone data collectors) or through the HTTP request to the

monitoring agent

(when collectors are executed as part of it) the verbose output mode providing

all the data can be selected.

When exporting just the status each status reporting collector will provide,

in its ``data`` section, at least the following field:

``status``

  summarizes the status of the component being monitored and consists of two

  subfields:

  ``code``

    It assumes a numeric value, encoded in such a way to allow using a bitset

    to easily distinguish which states are currently present in the whole cluster.

    If the bitwise OR of all the ``status`` fields is 0, the cluster is

    completely healty.

    The status codes are as follows:

    ``0``

      The collector can determine that everything is working as

      intended.

    ``1``

      Something is temporarily wrong but it is being automatically fixed by

      Ganeti.

      There is no need of external intervention.

    ``2``

      The collector can determine that something is wrong and Ganeti has no

      way to fix it autonomously. External intervention is required.

    ``4``

      The collector has failed to understand whether the status is good or

      bad. Further analysis is required. Interpret this status as a

      potentially dangerous situation.

  ``message``

    A message to better explain the reason of the status.

    The exact format of the message string is data collector dependent.

    The field is mandatory, but the content can be ``null`` if the code is

    ``0`` (working as intended) or ``1`` (being fixed automatically).

    If the status code is ``2``, the message should specify what has gone

    wrong.

    If the status code is ``4``, the message shoud explain why it was not

    possible to determine a proper status.

The ``data`` section will also contain all the fields describing the gathered

data, according to a collector-specific format.

Instance status

+++++++++++++++

At the moment each node knows which instances are running on it, which

instances it is primary for, but not the cause why an instance might not

be running. On the other hand we don't want to distribute full instance

"admin" status information to all nodes, because of the performance

impact this would have.

As such we propose that:

- Any operation that can affect instance status will have an optional

  "reason" attached to it (at opcode level). This can be used for

  example to distinguish an admin request, from a scheduled maintenance

  or an automated tool's work. If this reason is not passed, Ganeti will

  just use the information it has about the source of the request: for

  example a cli shutdown operation will have "cli:shutdown" as a reason,

  a cli failover operation will have "cli:failover". Operations coming

  from the remote API will use "rapi" instead of "cli". Of course

  setting a real site-specific reason is still preferred.

- RPCs that affect the instance status will be changed so that the

  "reason" and the version of the config object they ran on is passed to

  them. They will then export the new expected instance status, together

  with the associated reason and object version to the status report

  system, which then will export those themselves.

Monitoring and auditing systems can then use the reason to understand

the cause of an instance status, and they can use the timestamp to

understand the freshness of their data even in the absence of an atomic

cross-node reporting: for example if they see an instance "up" on a node

after seeing it running on a previous one, they can compare these values

to understand which data is freshest, and repoll the "older" node. Of

course if they keep seeing this status this represents an error (either

an instance continuously "flapping" between nodes, or an instance is

constantly up on more than one), which should be reported and acted

upon.

The instance status will be on each node, for the instances it is

primary for, and its ``data`` section of the report will contain a list

of instances, with at least the following fields for each instance:

``name``

  The name of the instance.

``uuid``

  The UUID of the instance (stable on name change).

``admin_state``

  The status of the instance (up/down/offline) as requested by the admin.

``actual_state``

  The actual status of the instance. It can be ``up``, ``down``, or

  ``hung`` if the instance is up but it appears to be completely stuck.

``uptime``

  The uptime of the instance (if it is up, "null" otherwise).

``mtime``

  The timestamp of the last known change to the instance state.

``state_reason``

  The last known reason for state change, described according to the

  following subfields:

  ``text``

    Either a user-provided reason (if any), or the name of the command that

    triggered the state change, as a fallback.

  ``jobID``

    The ID of the job that caused the state change.

  ``source``

    Where the state change was triggered (RAPI, CLI).

``status``

  It represents the status of the instance, and its format is the same as that

  of the ``status`` field of `Status reporting collectors`_.

Each hypervisor should provide its own instance status data collector, possibly

with the addition of more, specific, fields.

The ``category`` field of all of them will be ``instance``.

The ``kind`` field will be ``1``.

Note that as soon as a node knows it's not the primary anymore for an

instance it will stop reporting status for it: this means the instance

will either disappear, if it has been deleted, or appear on another

node, if it's been moved.

The ``code`` of the ``status`` field of the report of the Instance status data

collector will be:

``0``

  if ``status`` is ``0`` for all the instances it is reporting about.

``1``

  otherwise.

Storage status

++++++++++++++

The storage status collectors will be a series of data collectors

(drbd, rbd, plain, file) that will gather data about all the storage types

for the current node (this is right now hardcoded to the enabled storage

types, and in the future tied to the enabled storage pools for the nodegroup).

The ``name`` of each of these collector will reflect what storage type each of

them refers to.

The ``category`` field of these collector will be ``storage``.

The ``kind`` field will be ``1`` (`Status reporting collectors`_).

The ``data`` section of the report will provide at least the following fields:

``free``

  The amount of free space (in KBytes).

``used``

  The amount of used space (in KBytes).

``total``

  The total visible space (in KBytes).

Each specific storage type might provide more type-specific fields.

In case of error, the ``message`` subfield of the ``status`` field of the

report of the instance status collector will disclose the nature of the error

as a type specific information. Examples of these are "backend pv unavailable"

for lvm storage, "unreachable" for network based storage or "filesystem error"

for filesystem based implementations.

DRBD status

***********

This data collector will run only on nodes where DRBD is actually

present and it will gather information about DRBD devices.

Its ``kind`` in the report will be ``1`` (`Status reporting collectors`_).

Its ``category`` field in the report will contain the value ``storage``.

When executed in verbose mode, the ``data`` section of the report of this

collector will provide the following fields:

``versionInfo``

  Information about the DRBD version number, given by a combination of

  any (but at least one) of the following fields:

  ``version``

    The DRBD driver version.

  ``api``

    The API version number.

  ``proto``

    The protocol version.

  ``srcversion``

    The version of the source files.

  ``gitHash``

    Git hash of the source files.

  ``buildBy``

    Who built the binary, and, optionally, when.

``device``

  A list of structures, each describing a DRBD device (a minor) and containing

  the following fields:

  ``minor``

    The device minor number.

  ``connectionState``

    The state of the connection. If it is "Unconfigured", all the following

    fields are not present.

  ``localRole``

    The role of the local resource.

  ``remoteRole``

    The role of the remote resource.

  ``localState``

    The status of the local disk.

  ``remoteState``

    The status of the remote disk.

  ``replicationProtocol``

    The replication protocol being used.

  ``ioFlags``

    The input/output flags.

  ``perfIndicators``

    The performance indicators. This field will contain the following

    sub-fields:

    ``networkSend``

      KiB of data sent on the network.

    ``networkReceive``

      KiB of data received from the network.

    ``diskWrite``

      KiB of data written on local disk.

    ``diskRead``

      KiB of date read from the local disk.

    ``activityLog``

      Number of updates of the activity log.

    ``bitMap``

      Number of updates to the bitmap area of the metadata.

    ``localCount``

      Number of open requests to the local I/O subsystem.

    ``pending``

      Number of requests sent to the partner but not yet answered.

    ``unacknowledged``

      Number of requests received by the partner but still to be answered.

    ``applicationPending``

      Num of block input/output requests forwarded to DRBD but that have not yet

      been answered.

    ``epochs``

      (Optional) Number of epoch objects. Not provided by all DRBD versions.

    ``writeOrder``

      (Optional) Currently used write ordering method. Not provided by all DRBD

      versions.

    ``outOfSync``

      (Optional) KiB of storage currently out of sync. Not provided by all DRBD

      versions.

  ``syncStatus``

    (Optional) The status of the synchronization of the disk. This is present

    only if the disk is being synchronized, and includes the following fields:

    ``percentage``

      The percentage of synchronized data.

    ``progress``

      How far the synchronization is. Written as "x/y", where x and y are

      integer numbers expressed in the measurement unit stated in

      ``progressUnit``

    ``progressUnit``

      The measurement unit for the progress indicator.

    ``timeToFinish``

      The expected time before finishing the synchronization.

    ``speed``

      The speed of the synchronization.

    ``want``

      The desiderd speed of the synchronization.

    ``speedUnit``

      The measurement unit of the ``speed`` and ``want`` values. Expressed

      as "size/time".

  ``instance``

    The name of the Ganeti instance this disk is associated to.

Ganeti daemons status

+++++++++++++++++++++

Ganeti will report what information it has about its own daemons.

This should allow identifying possible problems with the Ganeti system itself:

for example memory leaks, crashes and high resource utilization should be

evident by analyzing this information.

The ``kind`` field will be ``1`` (`Status reporting collectors`_).

Each daemon will have its own data collector, and each of them will have

a ``category`` field valued ``daemon``.

When executed in verbose mode, their data section will include at least:

``memory``

  The amount of used memory.

``size_unit``

  The measurement unit used for the memory.

``uptime``

  The uptime of the daemon.

``CPU usage``

  How much cpu the daemon is using (percentage).

Any other daemon-specific information can be included as well in the ``data``

section.

Hypervisor resources report

+++++++++++++++++++++++++++

Each hypervisor has a view of system resources that sometimes is

different than the one the OS sees (for example in Xen the Node OS,

running as Dom0, has access to only part of those resources). In this

section we'll report all information we can in a "non hypervisor

specific" way. Each hypervisor can then add extra specific information

that is not generic enough be abstracted.

The ``kind`` field will be ``0`` (`Performance reporting collectors`_).

Each of the hypervisor data collectory will be of ``category``: ``hypervisor``.

Node OS resources report

++++++++++++++++++++++++

Since Ganeti assumes it's running on Linux, it's useful to export some

basic information as seen by the host system.

The ``category`` field of the report will be ``null``.

The ``kind`` field will be ``0`` (`Performance reporting collectors`_).

The ``data`` section will include:

``cpu_number``

  The number of available cpus.

``cpus``

  A list with one element per cpu, showing its average load.

``memory``

  The current view of memory (free, used, cached, etc.)

``filesystem``

  A list with one element per filesystem, showing a summary of the

  total/available space.

``NICs``

  A list with one element per network interface, showing the amount of

  sent/received data, error rate, IP address of the interface, etc.

``versions``

  A map using the name of a component Ganeti interacts (Linux, drbd,

  hypervisor, etc) as the key and its version number as the value.

Note that we won't go into any hardware specific details (e.g. querying a

node RAID is outside the scope of this, and can be implemented as a

plugin) but we can easily just report the information above, since it's

standard enough across all systems.

Instance disk status propagation

--------------------------------

As for the instance status Ganeti has now only partial information about

its instance disks: in particular each node is unaware of the disk to

instance mapping, that exists only on the master.

For this design doc we plan to fix this by changing all RPCs that create

a backend storage or that put an already existing one in use and passing

the relevant instance to the node. The node can then export these to the

status reporting tool.

While we haven't implemented these RPC changes yet, we'll use Confd to

fetch this information in the data collectors.

Plugin system

-------------

The monitoring system will be equipped with a plugin system that can

export specific local information through it.

The plugin system is expected to be used by local installations to

export any installation specific information that they want to be

monitored, about either hardware or software on their systems.

The plugin system will be in the form of either scripts or binaries whose output

will be inserted in the report.

Eventually support for other kinds of plugins might be added as well, such as

plain text files which will be inserted into the report, or local unix or

network sockets from which the information has to be read.  This should allow

most flexibility for implementing an efficient system, while being able to keep

it as simple as possible.

Data collectors

---------------

In order to ease testing as well as to make it simple to reuse this

subsystem it will be possible to run just the "data collectors" on each

node without passing through the agent daemon.

If a data collector is run independently, it should print on stdout its

report, according to the format corresponding to a single data collector

report object, as described in the previous paragraphs.

Mode of operation

-----------------

In order to be able to report information fast the monitoring agent

daemon will keep an in-memory or on-disk cache of the status, which will

be returned when queries are made. The status system will then

periodically check resources to make sure the status is up to date.

Different parts of the report will be queried at different speeds. These

will depend on:

- how often they vary (or we expect them to vary)

- how fast they are to query

- how important their freshness is

Of course the last parameter is installation specific, and while we'll

try to have defaults, it will be configurable. The first two instead we

can use adaptively to query a certain resource faster or slower

depending on those two parameters.

When run as stand-alone binaries, the data collector will not using any

caching system, and just fetch and return the data immediately.

Implementation place

--------------------

The status daemon will be implemented as a standalone Haskell daemon. In

the future it should be easy to merge multiple daemons into one with

multiple entry points, should we find out it saves resources and doesn't

impact functionality.

The libekg library should be looked at for easily providing metrics in

json format.

Implementation order

--------------------

We will implement the agent system in this order:

- initial example data collectors (eg. for drbd and instance status).

- initial daemon for exporting data, integrating the existing collectors

- plugin system

- RPC updates for instance status reasons and disk to instance mapping

- cache layer for the daemon

- more data collectors

Future work

===========

As a future step it can be useful to "centralize" all this reporting

data on a single place. This for example can be just the master node, or

all the master candidates. We will evaluate doing this after the first

node-local version has been developed and tested.

Another possible change is replacing the "read-only" RPCs with queries

to the agent system, thus having only one way of collecting information

from the nodes from a monitoring system and for Ganeti itself.

One extra feature we may need is a way to query for only sub-parts of

the report (eg. instances status only). This can be done by passing

arguments to the HTTP GET, which will be defined when we get to this

funtionality.

Finally the :doc:`autorepair system design <design-autorepair>`. system

(see its design) can be expanded to use the monitoring agent system as a

source of information to decide which repairs it can perform.

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