(Optional) Grafana Mimir query-scheduler
The query-scheduler is an optional, stateless component that retains a queue of queries to execute, and distributes the workload to available queriers.
The following flow describes how a query moves through a Grafana Mimir cluster:
- The query-frontend receives queries, and then either splits and shards them, or serves them from the cache.
- The query-frontend enqueues the queries into a query-scheduler.
- The query-scheduler stores the queries in an in-memory queue where they wait for a querier to pick them up.
- Queriers pick up the queries, and executes them.
- The querier sends results back to query-frontend, which then forwards the results to the client.
Benefits of using the query-scheduler
Query-scheduler enables the scaling of query-frontends. You might experience challenges when you scale query-frontend. To learn more about query-frontend scalability limits, refer to Why query-frontend scalability is limited.
How query-scheduler solves query-frontend scalability limits
When you use the query-scheduler, the queue is moved from the query-frontend to the query-scheduler, and the query-frontend can be scaled to any number of replicas.
The query-scheduler is affected by the same scalability limits as the query-frontend, but because a query-scheduler replica can handle high amounts of query throughput, scaling the query-scheduler to a number of replicas greater than
-querier.max-concurrent is typically not required, even for very large Grafana Mimir clusters.
To use the query-scheduler, query-frontends and queriers need to discover the addresses of query-scheduler instances. The query-scheduler supports two service discovery mechanisms:
- DNS-based service discovery
- Ring-based service discovery
DNS-based service discovery
To use the query-scheduler with DNS-based service discovery, configure the query-frontends and queriers to connect to the query-scheduler:
Note: The configured query-scheduler address should be in the
host:portformat. If multiple query-schedulers are running, the host should be a DNS resolving to all query-scheduler instances.
Note: The querier pulls queries only from the query-frontend or the query-scheduler, but not both.
-querier.scheduler-addressoptions are mutually exclusive, and only one option can be set.
Ring-based service discovery
To use the query-scheduler with ring-based service discovery, configure the query-schedulers to join their hash ring, and the query-frontends and queriers to discover query-scheduler instances via the ring:
- Configure the hash ring for the query-scheduler.
-query-scheduler.service-discovery-mode=ring(or its respective YAML configuration parameter) to query-scheduler, query-frontend and querier.
- Set the
-query-scheduler.ring.*flags (or their respective YAML configuration parameters) to query-scheduler, query-frontend and querier.
Migrate from DNS-based to ring-based service discovery
To migrate the query-scheduler from DNS-based service discovery to ring-based service discovery, perform the following steps:
Configure the query-scheduler instances to join a ring:
-query-scheduler.service-discovery-mode=ring # Configure the query-scheduler ring backend (e.g. "memberlist"). -query-scheduler.ring.store=<backend> # If the configured <backend> is "memberlist", then ensure memberlist is configured for the query-scheduler. -memberlist.join=<same as other Mimir components> # If the configured <backend> is "consul" or "etcd", then set their backend configuration # for the query-scheduler ring: # - Consul: -query-scheduler.ring.consul.* # - Ecd: -query-scheduler.ring.etcd.*
Wait until the query-scheduler instances have completed rolling out.
Ensure the changes have been successfully applied; open the query-scheduler ring status page and ensure all query-scheduler instances are registered to the ring. At this point, queriers and query-frontend are still discovering query-schedulers via DNS.
Configure query-frontend and querier instances to discover query-schedulers via the ring:
-query-scheduler.service-discovery-mode=ring # Remove the DNS-based service discovery configuration: # -query-frontend.scheduler-address # Configure the query-scheduler ring backend (e.g. "memberlist"). -query-scheduler.ring.store=<backend> # If the configured <backend> is "memberlist", then ensure memberlist is configured for the query-scheduler. -memberlist.join=<same as other Mimir components> # If the configured <backend> is "consul" or "etcd", then set their backend configuration # for the query-scheduler ring: # - Consul: -query-scheduler.ring.consul.* # - Ecd: -query-scheduler.ring.etcd.*
Note: If your Mimir cluster is deployed using Jsonnet, see Migrate query-scheduler from DNS-based to ring-based service discovery.
For high-availability, run two query-scheduler replicas.
If you’re running a Grafana Mimir cluster with a very high query throughput, you can add more query-scheduler replicas.
If you scale the query-scheduler, ensure that the number of replicas you add is less or equal than the configured