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diff --git a/doc/mgr/prometheus.rst b/doc/mgr/prometheus.rst new file mode 100644 index 00000000..87296be3 --- /dev/null +++ b/doc/mgr/prometheus.rst @@ -0,0 +1,314 @@ +.. _mgr-prometheus: + +================= +Prometheus Module +================= + +Provides a Prometheus exporter to pass on Ceph performance counters +from the collection point in ceph-mgr. Ceph-mgr receives MMgrReport +messages from all MgrClient processes (mons and OSDs, for instance) +with performance counter schema data and actual counter data, and keeps +a circular buffer of the last N samples. This module creates an HTTP +endpoint (like all Prometheus exporters) and retrieves the latest sample +of every counter when polled (or "scraped" in Prometheus terminology). +The HTTP path and query parameters are ignored; all extant counters +for all reporting entities are returned in text exposition format. +(See the Prometheus `documentation <https://prometheus.io/docs/instrumenting/exposition_formats/#text-format-details>`_.) + +Enabling prometheus output +========================== + +The *prometheus* module is enabled with:: + + ceph mgr module enable prometheus + +Configuration +------------- + +.. note:: + + The Prometheus manager module needs to be restarted for configuration changes to be applied. + +By default the module will accept HTTP requests on port ``9283`` on all IPv4 +and IPv6 addresses on the host. The port and listen address are both +configurable with ``ceph config-key set``, with keys +``mgr/prometheus/server_addr`` and ``mgr/prometheus/server_port``. This port +is registered with Prometheus's `registry +<https://github.com/prometheus/prometheus/wiki/Default-port-allocations>`_. + +:: + + ceph config set mgr mgr/prometheus/server_addr 0.0.0.0 + ceph config set mgr mgr/prometheus/server_port 9283 + +.. warning:: + + The ``scrape_interval`` of this module should always be set to match + Prometheus' scrape interval to work properly and not cause any issues. + +The Prometheus manager module is, by default, configured with a scrape interval +of 15 seconds. The scrape interval in the module is used for caching purposes +and to determine when a cache is stale. + +It is not recommended to use a scrape interval below 10 seconds. It is +recommended to use 15 seconds as scrape interval, though, in some cases it +might be useful to increase the scrape interval. + +To set a different scrape interval in the Prometheus module, set +``scrape_interval`` to the desired value:: + + ceph config set mgr mgr/prometheus/scrape_interval 20 + +On large clusters (>1000 OSDs), the time to fetch the metrics may become +significant. Without the cache, the Prometheus manager module could, +especially in conjunction with multiple Prometheus instances, overload the +manager and lead to unresponsive or crashing Ceph manager instances. Hence, +the cache is enabled by default and cannot be disabled. This means that there +is a possibility that the cache becomes stale. The cache is considered stale +when the time to fetch the metrics from Ceph exceeds the configured +``scrape_interval``. + +If that is the case, **a warning will be logged** and the module will either + +* respond with a 503 HTTP status code (service unavailable) or, +* it will return the content of the cache, even though it might be stale. + +This behavior can be configured. By default, it will return a 503 HTTP status +code (service unavailable). You can set other options using the ``ceph config +set`` commands. + +To tell the module to respond with possibly stale data, set it to ``return``:: + + ceph config set mgr mgr/prometheus/stale_cache_strategy return + +To tell the module to respond with "service unavailable", set it to ``fail``:: + + ceph config set mgr mgr/prometheus/stale_cache_strategy fail + +.. _prometheus-rbd-io-statistics: + +RBD IO statistics +----------------- + +The module can optionally collect RBD per-image IO statistics by enabling +dynamic OSD performance counters. The statistics are gathered for all images +in the pools that are specified in the ``mgr/prometheus/rbd_stats_pools`` +configuration parameter. The parameter is a comma or space separated list +of ``pool[/namespace]`` entries. If the namespace is not specified the +statistics are collected for all namespaces in the pool. + +Example to activate the RBD-enabled pools ``pool1``, ``pool2`` and ``poolN``:: + + ceph config set mgr mgr/prometheus/rbd_stats_pools "pool1,pool2,poolN" + +The module makes the list of all available images scanning the specified +pools and namespaces and refreshes it periodically. The period is +configurable via the ``mgr/prometheus/rbd_stats_pools_refresh_interval`` +parameter (in sec) and is 300 sec (5 minutes) by default. The module will +force refresh earlier if it detects statistics from a previously unknown +RBD image. + +Example to turn up the sync interval to 10 minutes:: + + ceph config set mgr mgr/prometheus/rbd_stats_pools_refresh_interval 600 + +Statistic names and labels +========================== + +The names of the stats are exactly as Ceph names them, with +illegal characters ``.``, ``-`` and ``::`` translated to ``_``, +and ``ceph_`` prefixed to all names. + + +All *daemon* statistics have a ``ceph_daemon`` label such as "osd.123" +that identifies the type and ID of the daemon they come from. Some +statistics can come from different types of daemon, so when querying +e.g. an OSD's RocksDB stats, you would probably want to filter +on ceph_daemon starting with "osd" to avoid mixing in the monitor +rocksdb stats. + + +The *cluster* statistics (i.e. those global to the Ceph cluster) +have labels appropriate to what they report on. For example, +metrics relating to pools have a ``pool_id`` label. + + +The long running averages that represent the histograms from core Ceph +are represented by a pair of ``<name>_sum`` and ``<name>_count`` metrics. +This is similar to how histograms are represented in `Prometheus <https://prometheus.io/docs/concepts/metric_types/#histogram>`_ +and they can also be treated `similarly <https://prometheus.io/docs/practices/histograms/>`_. + +Pool and OSD metadata series +---------------------------- + +Special series are output to enable displaying and querying on +certain metadata fields. + +Pools have a ``ceph_pool_metadata`` field like this: + +:: + + ceph_pool_metadata{pool_id="2",name="cephfs_metadata_a"} 1.0 + +OSDs have a ``ceph_osd_metadata`` field like this: + +:: + + ceph_osd_metadata{cluster_addr="172.21.9.34:6802/19096",device_class="ssd",ceph_daemon="osd.0",public_addr="172.21.9.34:6801/19096",weight="1.0"} 1.0 + + +Correlating drive statistics with node_exporter +----------------------------------------------- + +The prometheus output from Ceph is designed to be used in conjunction +with the generic host monitoring from the Prometheus node_exporter. + +To enable correlation of Ceph OSD statistics with node_exporter's +drive statistics, special series are output like this: + +:: + + ceph_disk_occupation{ceph_daemon="osd.0",device="sdd", exported_instance="myhost"} + +To use this to get disk statistics by OSD ID, use either the ``and`` operator or +the ``*`` operator in your prometheus query. All metadata metrics (like `` +ceph_disk_occupation`` have the value 1 so they act neutral with ``*``. Using ``*`` +allows to use ``group_left`` and ``group_right`` grouping modifiers, so that +the resulting metric has additional labels from one side of the query. + +See the +`prometheus documentation`__ for more information about constructing queries. + +__ https://prometheus.io/docs/prometheus/latest/querying/basics + +The goal is to run a query like + +:: + + rate(node_disk_bytes_written[30s]) and on (device,instance) ceph_disk_occupation{ceph_daemon="osd.0"} + +Out of the box the above query will not return any metrics since the ``instance`` labels of +both metrics don't match. The ``instance`` label of ``ceph_disk_occupation`` +will be the currently active MGR node. + + The following two section outline two approaches to remedy this. + +Use label_replace +================= + +The ``label_replace`` function (cp. +`label_replace documentation <https://prometheus.io/docs/prometheus/latest/querying/functions/#label_replace>`_) +can add a label to, or alter a label of, a metric within a query. + +To correlate an OSD and its disks write rate, the following query can be used: + +:: + + label_replace(rate(node_disk_bytes_written[30s]), "exported_instance", "$1", "instance", "(.*):.*") and on (device,exported_instance) ceph_disk_occupation{ceph_daemon="osd.0"} + +Configuring Prometheus server +============================= + +honor_labels +------------ + +To enable Ceph to output properly-labeled data relating to any host, +use the ``honor_labels`` setting when adding the ceph-mgr endpoints +to your prometheus configuration. + +This allows Ceph to export the proper ``instance`` label without prometheus +overwriting it. Without this setting, Prometheus applies an ``instance`` label +that includes the hostname and port of the endpoint that the series came from. +Because Ceph clusters have multiple manager daemons, this results in an +``instance`` label that changes spuriously when the active manager daemon +changes. + +If this is undesirable a custom ``instance`` label can be set in the +Prometheus target configuration: you might wish to set it to the hostname +of your first mgr daemon, or something completely arbitrary like "ceph_cluster". + +node_exporter hostname labels +----------------------------- + +Set your ``instance`` labels to match what appears in Ceph's OSD metadata +in the ``instance`` field. This is generally the short hostname of the node. + +This is only necessary if you want to correlate Ceph stats with host stats, +but you may find it useful to do it in all cases in case you want to do +the correlation in the future. + +Example configuration +--------------------- + +This example shows a single node configuration running ceph-mgr and +node_exporter on a server called ``senta04``. Note that this requires to add the +appropriate instance label to every ``node_exporter`` target individually. + +This is just an example: there are other ways to configure prometheus +scrape targets and label rewrite rules. + +prometheus.yml +~~~~~~~~~~~~~~ + +:: + + global: + scrape_interval: 15s + evaluation_interval: 15s + + scrape_configs: + - job_name: 'node' + file_sd_configs: + - files: + - node_targets.yml + - job_name: 'ceph' + honor_labels: true + file_sd_configs: + - files: + - ceph_targets.yml + + +ceph_targets.yml +~~~~~~~~~~~~~~~~ + + +:: + + [ + { + "targets": [ "senta04.mydomain.com:9283" ], + "labels": {} + } + ] + + +node_targets.yml +~~~~~~~~~~~~~~~~ + +:: + + [ + { + "targets": [ "senta04.mydomain.com:9100" ], + "labels": { + "instance": "senta04" + } + } + ] + + +Notes +===== + +Counters and gauges are exported; currently histograms and long-running +averages are not. It's possible that Ceph's 2-D histograms could be +reduced to two separate 1-D histograms, and that long-running averages +could be exported as Prometheus' Summary type. + +Timestamps, as with many Prometheus exporters, are established by +the server's scrape time (Prometheus expects that it is polling the +actual counter process synchronously). It is possible to supply a +timestamp along with the stat report, but the Prometheus team strongly +advises against this. This means that timestamps will be delayed by +an unpredictable amount; it's not clear if this will be problematic, +but it's worth knowing about. |