arguments.md

Cortex Arguments Explained

General Notes

Cortex has evolved over several years, and the command-line options sometimes reflect this heritage. In some cases the default value for options is not the recommended value, and in some cases names do not reflect the true meaning. We do intend to clean this up, but it requires a lot of care to avoid breaking existing installations. In the meantime we regret the inconvenience.

Duration arguments should be specified with a unit like 5s or 3h. Valid time units are "ms", "s", "m", "h".

Querier

• -querier.max-concurrent

  The maximum number of top-level PromQL queries that will execute at the same time, per querier process. If using the query frontend, this should be set to at least (querier.worker-parallelism * number of query frontend replicas). Otherwise queries may queue in the queriers and not the frontend, which will affect QoS.

• -querier.query-parallelism

  This refers to database queries against the store (e.g. Bigtable or DynamoDB). This is the max subqueries run in parallel per higher-level query.

• -querier.timeout

  The timeout for a top-level PromQL query.

• -querier.max-samples

  Maximum number of samples a single query can load into memory, to avoid blowing up on enormous queries.

The next three options only apply when the querier is used together with the Query Frontend:

• -querier.frontend-address

  Address of query frontend service, used by workers to find the frontend which will give them queries to execute.

• -querier.dns-lookup-period

  How often the workers will query DNS to re-check where the frontend is.

• -querier.worker-parallelism

  Number of simultaneous queries to process, per worker process. See note on -querier.max-concurrent

Querier and Ruler

The ingester query API was improved over time, but defaults to the old behaviour for backwards-compatibility. For best results both of these next two flags should be set to true:

• -querier.batch-iterators

  This uses iterators to execute query, as opposed to fully materialising the series in memory, and fetches multiple results per loop.

• -querier.ingester-streaming

  Use streaming RPCs to query ingester, to reduce memory pressure in the ingester.

• -querier.iterators

  This is similar to -querier.batch-iterators but less efficient. If both iterators and batch-iterators are true, batch-iterators will take precedence.

• -promql.lookback-delta

  Time since the last sample after which a time series is considered stale and ignored by expression evaluations.

Query Frontend

• -querier.align-querier-with-step

  If set to true, will cause the query frontend to mutate incoming queries and align their start and end parameters to the step parameter of the query. This improves the cacheability of the query results.

• -querier.split-queries-by-day

  If set to true, will case the query frontend to split multi-day queries into multiple single-day queries and execute them in parallel.

• -querier.cache-results

  If set to true, will cause the querier to cache query results. The cache will be used to answer future, overlapping queries. The query frontend calculates extra queries required to fill gaps in the cache.

• -frontend.max-cache-freshness

  When caching query results, it is desirable to prevent the caching of very recent results that might still be in flux. Use this parameter to configure the age of results that should be excluded.

• -memcached.{hostname, service, timeout}

  Use these flags to specify the location and timeout of the memcached cluster used to cache query results.

• -redis.{endpoint, timeout}

  Use these flags to specify the location and timeout of the Redis service used to cache query results.

Distributor

• -distributor.shard-by-all-labels

  In the original Cortex design, samples were sharded amongst distributors by the combination of (userid, metric name). Sharding by metric name was designed to reduce the number of ingesters you need to hit on the read path; the downside was that you could hotspot the write path.

  In hindsight, this seems like the wrong choice: we do many orders of magnitude more writes than reads, and ingester reads are in-memory and cheap. It seems the right thing to do is to use all the labels to shard, improving load balancing and support for very high cardinality metrics.

  Set this flag to true for the new behaviour.

  Upgrade notes: As this flag also makes all queries always read from all ingesters, the upgrade path is pretty trivial; just enable the flag. When you do enable it, you'll see a spike in the number of active series as the writes are "reshuffled" amongst the ingesters, but over the next stale period all the old series will be flushed, and you should end up with much better load balancing. With this flag enabled in the queriers, reads will always catch all the data from all ingesters.

• -distributor.extra-query-delay This is used by a component with an embedded distributor (Querier and Ruler) to control how long to wait until sending more than the minimum amount of queries needed for a successful response.

• distributor.ha-tracker.enable-for-all-users Flag to enable, for all users, handling of samples with external labels identifying replicas in an HA Prometheus setup. This defaults to false, and is technically defined in the Distributor limits.

• distributor.ha-tracker.enable Enable the distributors HA tracker so that it can accept samples from Prometheus HA replicas gracefully (requires labels). Global (for distributors), this ensures that the necessary internal data structures for the HA handling are created. The option enable-for-all-users is still needed to enable ingestion of HA samples for all users.

Ring/HA Tracker Store

The KVStore client is used by both the Ring and HA Tracker.

• {ring,distributor.ha-tracker}.prefix The prefix for the keys in the store. Should end with a /. For example with a prefix of foo/, the key bar would be stored under foo/bar.
• {ring,distributor.ha-tracker}.store Backend storage to use for the ring (consul, etcd, inmemory).

Consul

By default these flags are used to configure Consul used for the ring. To configure Consul for the HA tracker, prefix these flags with distributor.ha-tracker.

• consul.hostname Hostname and port of Consul.
• consul.acltoken ACL token used to interact with Consul.
• consul.client-timeout HTTP timeout when talking to Consul.
• consul.consistent-reads Enable consistent reads to Consul.

etcd

By default these flags are used to configure etcd used for the ring. To configure etcd for the HA tracker, prefix these flags with distributor.ha-tracker.

• etcd.endpoints The etcd endpoints to connect to.
• etcd.dial-timeout The timeout for the etcd connection.
• etcd.max-retries The maximum number of retries to do for failed ops.

memberlist (EXPERIMENTAL)

Flags for configuring KV store based on memberlist library. This feature is experimental, please don't use it yet.

• memberlist.nodename Name of the node in memberlist cluster. Defaults to hostname.
• memberlist.retransmit-factor Multiplication factor used when sending out messages (factor * log(N+1)). If not set, default value is used.
• memberlist.join Other cluster members to join. Can be specified multiple times.
• memberlist.abort-if-join-fails If this node fails to join memberlist cluster, abort.
• memberlist.left-ingesters-timeout How long to keep LEFT ingesters in the ring. Note: this is only used for gossiping, LEFT ingesters are otherwise invisible.
• memberlist.leave-timeout Timeout for leaving memberlist cluster.
• memberlist.gossip-interval How often to gossip with other cluster members. Uses memberlist LAN defaults if 0.
• memberlist.gossip-nodes How many nodes to gossip with in each gossip interval. Uses memberlist LAN defaults if 0.
• memberlist.pullpush-interval How often to use pull/push sync. Uses memberlist LAN defaults if 0.
• memberlist.bind-addr IP address to listen on for gossip messages. Multiple addresses may be specified. Defaults to 0.0.0.0.
• memberlist.bind-port Port to listen on for gossip messages. Defaults to 7946.
• memberlist.packet-dial-timeout Timeout used when connecting to other nodes to send packet.
• memberlist.packet-write-timeout Timeout for writing 'packet' data.
• memberlist.transport-debug Log debug transport messages. Note: global log.level must be at debug level as well.

HA Tracker

HA tracking has two of it's own flags:

• distributor.ha-tracker.cluster Prometheus label to look for in samples to identify a Prometheus HA cluster. (default "cluster")
• distributor.ha-tracker.replica Prometheus label to look for in samples to identify a Prometheus HA replica. (default "__replica__")

It's reasonable to assume people probably already have a cluster label, or something similar. If not, they should add one along with __replica__ via external labels in their Prometheus config. If you stick to these default values your Prometheus config could look like this (POD_NAME is an environment variable which must be set by you):

global:
  external_labels:
    cluster: clustername
    __replica__: $POD_NAME

HA Tracking looks for the two labels (which can be overwritten per user)

It also talks to a KVStore and has it's own copies of the same flags used by the Distributor to connect to for the ring.

• distributor.ha-tracker.failover-timeout If we don't receive any samples from the accepted replica for a cluster in this amount of time we will failover to the next replica we receive a sample from. This value must be greater than the update timeout (default 30s)
• distributor.ha-tracker.store Backend storage to use for the ring (consul, etcd, inmemory). (default "consul")
• distributor.ha-tracker.update-timeout Update the timestamp in the KV store for a given cluster/replica only after this amount of time has passed since the current stored timestamp. (default 15s)

Ingester

• -ingester.max-chunk-age

  The maximum duration of a timeseries chunk in memory. If a timeseries runs for longer than this the current chunk will be flushed to the store and a new chunk created. (default 12h)

• -ingester.max-chunk-idle

  If a series doesn't receive a sample for this duration, it is flushed and removed from memory.

• -ingester.max-stale-chunk-idle

  If a series receives a staleness marker, then we wait for this duration to get another sample before we close and flush this series, removing it from memory. You want it to be at least 2x the scrape interval as you don't want a single failed scrape to cause a chunk flush.

• -ingester.chunk-age-jitter

  To reduce load on the database exactly 12 hours after starting, the age limit is reduced by a varying amount up to this. (default 20m)

• -ingester.spread-flushes

  Makes the ingester flush each timeseries at a specific point in the max-chunk-age cycle. This means multiple replicas of a chunk are very likely to contain the same contents which cuts chunk storage space by up to 66%. Set -ingester.chunk-age-jitter to 0 when using this option. If a chunk cache is configured (via -memcached.hostname) then duplicate chunk writes are skipped which cuts write IOPs.

• -ingester.join-after

  How long to wait in PENDING state during the hand-over process. (default 0s)

• -ingester.max-transfer-retries

  How many times a LEAVING ingester tries to find a PENDING ingester during the hand-over process. Each attempt takes a second or so. Negative value or zero disables hand-over process completely. (default 10)

• -ingester.normalise-tokens

  Write out "normalised" tokens to the ring. Normalised tokens consume less memory to encode and decode; as the ring is unmarshalled regularly, this significantly reduces memory usage of anything that watches the ring.

  Before enabling, rollout a version of Cortex that supports normalised token for all jobs that interact with the ring, then rollout with this flag set to true on the ingesters. The new ring code can still read and write the old ring format, so is backwards compatible.

• -ingester.chunk-encoding

  Pick one of the encoding formats for timeseries data, which have different performance characteristics. Bigchunk uses the Prometheus V2 code, and expands in memory to arbitrary length. Varbit, Delta and DoubleDelta use Prometheus V1 code, and are fixed at 1K per chunk. Defaults to DoubleDelta, but we recommend Bigchunk.

• -store.bigchunk-size-cap-bytes

  When using bigchunks, start a new bigchunk and flush the old one if the old one reaches this size. Use this setting to limit memory growth of ingesters with a lot of timeseries that last for days.

• -ingester-client.expected-timeseries

  When push requests arrive, pre-allocate this many slots to decode them. Tune this setting to reduce memory allocations and garbage. This should match the max_samples_per_send in your queue_config for Prometheus.

• -ingester-client.expected-samples-per-series

  When push requests arrive, pre-allocate this many slots to decode them. Tune this setting to reduce memory allocations and garbage. Under normal conditions, Prometheus scrapes should arrive with one sample per series.

• -ingester-client.expected-labels

  When push requests arrive, pre-allocate this many slots to decode them. Tune this setting to reduce memory allocations and garbage. The optimum value will depend on how many labels are sent with your timeseries samples.

• -store.chunk-cache-stubs

  Where you don't want to cache every chunk written by ingesters, but you do want to take advantage of chunk write deduplication, this option will make ingesters write a placeholder to the cache for each chunk. Make sure you configure ingesters with a different cache to queriers, which need the whole value.

Ingester, Distributor & Querier limits.

Cortex implements various limits on the requests it can process, in order to prevent a single tenant overwhelming the cluster. There are various default global limits which apply to all tenants which can be set on the command line. These limits can also be overridden on a per-tenant basis, using a configuration file. Specify the filename for the override configuration file using the -limits.per-user-override-config=<filename> flag. The override file will be re-read every 10 seconds by default - this can also be controlled using the -limits.per-user-override-period=10s flag.

The override file should be in YAML format and contain a single overrides field, which itself is a map of tenant ID (same values as passed in the X-Scope-OrgID header) to the various limits. An example overrides.yml could look like:

overrides:
  tenant1:
    ingestion_rate: 10000
    max_series_per_metric: 100000
    max_series_per_query: 100000
  tenant2:
    max_samples_per_query: 1000000
    max_series_per_metric: 100000
    max_series_per_query: 100000

When running Cortex on Kubernetes, store this file in a config map and mount it in each services' containers. When changing the values there is no need to restart the services, unless otherwise specified.

Valid fields are (with their corresponding flags for default values):

• ingestion_rate / -distributor.ingestion-rate-limit

• ingestion_burst_size / -distributor.ingestion-burst-size

  The per-tenant rate limit (and burst size), in samples per second. Enforced on a per distributor basis, actual effective rate limit will be N times higher, where N is the number of distributor replicas.

  NB Limits are reset every -distributor.limiter-reload-period, as such if you set a very high burst limit it will never be hit.

• max_label_name_length / -validation.max-length-label-name

• max_label_value_length / -validation.max-length-label-value

• max_label_names_per_series / -validation.max-label-names-per-series

  Also enforced by the distributor, limits on the on length of labels and their values, and the total number of labels allowed per series.

• reject_old_samples / -validation.reject-old-samples

• reject_old_samples_max_age / -validation.reject-old-samples.max-age

• creation_grace_period / -validation.create-grace-period

  Also enforce by the distributor, limits on how far in the past (and future) timestamps that we accept can be.

• max_series_per_user / -ingester.max-series-per-user

• max_series_per_metric / -ingester.max-series-per-metric

  Enforced by the ingesters; limits the number of active series a user (or a given metric) can have. When running with -distributor.shard-by-all-labels=false (the default), this limit will enforce the maximum number of series a metric can have 'globally', as all series for a single metric will be sent to the same replication set of ingesters. This is not the case when running with -distributor.shard-by-all-labels=true, so the actual limit will be N/RF times higher, where N is number of ingester replicas and RF is configured replication factor.

  An active series is a series to which a sample has been written in the last -ingester.max-chunk-idle duration, which defaults to 5 minutes.

• max_global_series_per_user / -ingester.max-global-series-per-user

• max_global_series_per_metric / -ingester.max-global-series-per-metric

  Like max_series_per_user and max_series_per_metric, but the limit is enforced across the cluster. Each ingester is configured with a local limit based on the replication factor, the -distributor.shard-by-all-labels setting and the current number of healthy ingesters, and is kept updated whenever the number of ingesters change.

  Requires -distributor.replication-factor and -distributor.shard-by-all-labels set for the ingesters too.

• max_series_per_query / -ingester.max-series-per-query

• max_samples_per_query / -ingester.max-samples-per-query

  Limits on the number of timeseries and samples returns by a single ingester during a query.

Storage

• s3.force-path-style

  Set this to true to force the request to use path-style addressing (http://s3.amazonaws.com/BUCKET/KEY). By default, the S3 client will use virtual hosted bucket addressing when possible (http://BUCKET.s3.amazonaws.com/KEY).