.. _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 `_.) 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 `_. :: 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 ``_sum`` and ``_count`` metrics. This is similar to how histograms are represented in `Prometheus `_ and they can also be treated `similarly `_. 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 `_) 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.