NOTE: It is recommended to keep deploying rules inside the relevant Prometheus servers locally. Use ruler only on specific cases. Read details below why.
The rule component should in particular not be used to circumvent solving rule deployment properly at the configuration management level.
The rule component evaluates Prometheus recording and alerting rules against chosen query API via repeated --query (or FileSD via --query.sd). If more than one query is passed, round robin balancing is performed.
Rule results are written back to disk in the Prometheus 2.0 storage format. Rule nodes at the same time participate in the system as source store nodes, which means that they expose StoreAPI and upload their generated TSDB blocks to an object store.
You can think of Rule as a simplified Prometheus that does not require a sidecar and does not scrape and do PromQL evaluation (no QueryAPI).
The data of each Rule node can be labeled to satisfy the clusters labeling scheme. High-availability pairs can be run in parallel and should be distinguished by the designated replica label, just like regular Prometheus servers. Read more about Ruler in HA here
$ thanos rule \
--data-dir "/path/to/data" \
--eval-interval "30s" \
--rule-file "/path/to/rules/*.rules.yaml" \
--alert.query-url "http://0.0.0.0:9090" \ # This tells what query URL to link to in UI.
--alertmanagers.url "alert.thanos.io" \
--query "query.example.org" \
--query "query2.example.org" \
--objstore.config-file "bucket.yml" \
--label 'monitor_cluster="cluster1"'
--label 'replica="A"
Ruler has conceptual tradeoffs that might not be favorable for most use cases. The main tradeoff is its dependence on query reliability. For Prometheus it is unlikely to have alert/recording rule evaluation failure as evaluation is local.
For Ruler the read path is distributed, since most likely Ruler is querying Thanos Querier which gets data from remote Store APIs.
This means that query failure are more likely to happen, that’s why clear strategy on what will happen to alert and during query unavailability is the key.
See this on initial info.
Rule allows you to specify rule groups with additional fields that control PartialResponseStrategy e.g:
groups:
- name: "warn strategy"
partial_response_strategy: "warn"
rules:
- alert: "some"
expr: "up"
- name: "abort strategy"
partial_response_strategy: "abort"
rules:
- alert: "some"
expr: "up"
- name: "by default strategy is abort"
rules:
- alert: "some"
expr: "up"
It is recommended to keep partial response as abort for alerts and that is the default as well.
Essentially, for alerting, having partial response can result in symptoms being missed by Rule’s alert.
To be sure that alerting works it is essential to monitor Ruler and alert from another Scraper (Prometheus + sidecar) that sits in same cluster.
The most important metrics to alert on are:
thanos_alert_sender_alerts_dropped_total. If greater than 0, it means that alerts triggered by Rule are not being sent to alertmanager which might indicate connection, incompatibility or misconfiguration problems.
prometheus_rule_evaluation_failures_total. If greater than 0, it means that that rule failed to be evaluated, which results in either gap in rule or potentially ignored alert. Alert heavily on this if this happens for longer than your alert thresholds. strategy label will tell you if failures comes from rules that tolerate partial response or not.
prometheus_rule_group_last_duration_seconds < prometheus_rule_group_interval_seconds If the difference is large, it means that rule evaluation took more time than the scheduled interval. It can indicate that your query backend (e.g Querier) takes too much time to evaluate the query, i.e. that it is not fast enough to fill the rule. This might indicate other problems like slow StoreAPis or too complex query expression in rule.
thanos_rule_evaluation_with_warnings_total. If you choose to use Rules and Alerts with partial response strategy’s value as “warn”, this metric will tell you how many evaluation ended up with some kind of warning. To see the actual warnings see WARN log level. This might suggest that those evaluations return partial response and might not be accurate.
Those metrics are important for vanilla Prometheus as well, but even more important when we rely on (sometimes WAN) network.
// TODO(bwplotka): Rereview them after recent changes in metrics.
See alerts for more example alerts for ruler.
NOTE: It is also recommended to set a mocked Alert on Ruler that checks if Query is up. This might be something simple like vector(1) query, just to check if Querier is live.
As rule nodes outsource query processing to query nodes, they should generally experience little load. If necessary, functional sharding can be applied by splitting up the sets of rules between HA pairs. Rules are processed with deduplicated data according to the replica label configured on query nodes.
It is mandatory to add certain external labels to indicate the ruler origin (e.g label='replica="A"' or for cluster). Otherwise running multiple ruler replicas will be not possible, resulting in clash during compaction.
NOTE: It is advised to put different external labels than labels given by other sources we are recording or alerting against.
For example:
mon1 and we have Prometheus in cluster eu1cluster=eu1 for Prometheus and cluster=mon1 for Ruler.ScraperIsDown alert that monitors service from work1 cluster.ScraperIsDown{cluster=mon1} since external labels always replace source labels.This effectively drops the important metadata and makes it impossible to tell in what exactly cluster the ScraperIsDown alert found problem without falling back to manual query.
On HTTP address Ruler exposes its UI that shows mainly Alerts and Rules page (similar to Prometheus Alerts page). Each alert is linked to the query that the alert is performing, which you can click to navigate to the configured alert.query-url.
Ruler aims to use a similar approach to the one that Prometheus has. You can configure external labels, as well as simple relabelling.
In case of Ruler in HA you need to make sure you have the following labelling setup:
cluster="eu1", replica="A" and cluster=eu1, replica="B" by using --label flag.--alertmanager.label-drop="replica".Full relabelling is planned to be done in future and is tracked here: https://github.com/improbable-eng/thanos/issues/660
usage: thanos rule [<flags>]
ruler evaluating Prometheus rules against given Query nodes, exposing Store API
and storing old blocks in bucket
Flags:
-h, --help Show context-sensitive help (also try
--help-long and --help-man).
--version Show application version.
--log.level=info Log filtering level.
--log.format=logfmt Log format to use.
--gcloudtrace.project=GCLOUDTRACE.PROJECT
GCP project to send Google Cloud Trace tracings
to. If empty, tracing will be disabled.
--gcloudtrace.sample-factor=1
How often we send traces (1/<sample-factor>).
If 0 no trace will be sent periodically, unless
forced by baggage item. See
`pkg/tracing/tracing.go` for details.
--http-address="0.0.0.0:10902"
Listen host:port for HTTP endpoints.
--grpc-address="0.0.0.0:10901"
Listen ip:port address for gRPC endpoints
(StoreAPI). Make sure this address is routable
from other components.
--grpc-server-tls-cert="" TLS Certificate for gRPC server, leave blank to
disable TLS
--grpc-server-tls-key="" TLS Key for the gRPC server, leave blank to
disable TLS
--grpc-server-tls-client-ca=""
TLS CA to verify clients against. If no client
CA is specified, there is no client
verification on server side. (tls.NoClientCert)
--label=<name>="<value>" ...
Labels to be applied to all generated metrics
(repeated). Similar to external labels for
Prometheus, used to identify ruler and its
blocks as unique source.
--data-dir="data/" data directory
--rule-file=rules/ ... Rule files that should be used by rule manager.
Can be in glob format (repeated).
--eval-interval=30s The default evaluation interval to use.
--tsdb.block-duration=2h Block duration for TSDB block.
--tsdb.retention=48h Block retention time on local disk.
--alertmanagers.url=ALERTMANAGERS.URL ...
Alertmanager replica URLs to push firing
alerts. Ruler claims success if push to at
least one alertmanager from discovered
succeeds. The scheme may be prefixed with
'dns+' or 'dnssrv+' to detect Alertmanager IPs
through respective DNS lookups. The port
defaults to 9093 or the SRV record's value. The
URL path is used as a prefix for the regular
Alertmanager API path.
--alertmanagers.send-timeout=10s
Timeout for sending alerts to alertmanager
--alert.query-url=ALERT.QUERY-URL
The external Thanos Query URL that would be set
in all alerts 'Source' field
--alert.label-drop=ALERT.LABEL-DROP ...
Labels by name to drop before sending to
alertmanager. This allows alert to be
deduplicated on replica label (repeated).
Similar Prometheus alert relabelling
--web.route-prefix="" Prefix for API and UI endpoints. This allows
thanos UI to be served on a sub-path. This
option is analogous to --web.route-prefix of
Promethus.
--web.external-prefix="" Static prefix for all HTML links and redirect
URLs in the UI query web interface. Actual
endpoints are still served on / or the
web.route-prefix. This allows thanos UI to be
served behind a reverse proxy that strips a URL
sub-path.
--web.prefix-header="" Name of HTTP request header used for dynamic
prefixing of UI links and redirects. This
option is ignored if web.external-prefix
argument is set. Security risk: enable this
option only if a reverse proxy in front of
thanos is resetting the header. The
--web.prefix-header=X-Forwarded-Prefix option
can be useful, for example, if Thanos UI is
served via Traefik reverse proxy with
PathPrefixStrip option enabled, which sends the
stripped prefix value in X-Forwarded-Prefix
header. This allows thanos UI to be served on a
sub-path.
--objstore.config-file=<bucket.config-yaml-path>
Path to YAML file that contains object store
configuration.
--objstore.config=<bucket.config-yaml>
Alternative to 'objstore.config-file' flag.
Object store configuration in YAML.
--query=<query> ... Addresses of statically configured query API
servers (repeatable). The scheme may be
prefixed with 'dns+' or 'dnssrv+' to detect
query API servers through respective DNS
lookups.
--query.sd-files=<path> ...
Path to file that contain addresses of query
peers. The path can be a glob pattern
(repeatable).
--query.sd-interval=5m Refresh interval to re-read file SD files.
(used as a fallback)
--query.sd-dns-interval=30s
Interval between DNS resolutions.