Query frontend example

Disclaimer

This aims to be a general purpose example; there are a number of substitutions to make for it to work correctly. These variables take the form of <variable_name>. You should override them with specifics to your environment.

Use case

It’s a common occurrence to start running Grafana Loki as a single binary while trying it out in order to simplify deployments and defer learning the (initially unnecessary) nitty gritty details. As we become more comfortable with its paradigms and begin migrating towards a more production ready deployment there are a number of things to be aware of. A common bottleneck is on the read path: queries that executed effortlessly on small data sets may churn to a halt on larger ones. Sometimes we can solve this with more queriers. However, that doesn’t help when our queries are too large for a single querier to execute. Then we need the query frontend.

Parallelization

One of the most important functions of the query frontend is the ability to split larger queries into smaller ones, execute them in parallel, and stitch the results back together. How often it splits them is determined by the querier.split-queries-by-interval flag or the yaml config query_range.split_queriers_by_interval. With this set to 1h, the frontend will dissect a day long query into 24 one hour queries, distribute them to the queriers, and collect the results. This is immensely helpful in production environments as it not only allows us to perform larger queries via aggregation, but also evens the work distribution across queriers so that one or two are not stuck with impossibly large queries while others are left idle.

Kubernetes Deployment

ConfigMap

Use this ConfigMap to get the benefits of query parallelisation and caching with the query-frontend component.

apiVersion: v1
kind: ConfigMap
metadata:
  name: loki-frontend
  namespace: <namespace>
data:
  config.yaml: |
    # Disable the requirement that every request to Loki has a
    # X-Scope-OrgID header. `fake` will be substituted in instead.
    auth_enabled: false

    # We don't want the usual /api/prom prefix.
    http_prefix:

    server:
      http_listen_port: 3100

    query_range:
      # make queries more cache-able by aligning them with their step intervals
      align_queries_with_step: true
      max_retries: 5
      cache_results: true

      results_cache:
        cache:
          # We're going to use the embedded cache
          embedded_cache:
            enabled: true
            max_size_mb: 100
            ttl: 24h

    limits_config:
      max_cache_freshness_per_query: '10m'
      # parallelize queries in 15min intervals
      split_queries_by_interval: 15m

    frontend:
      log_queries_longer_than: 5s
      downstream_url: http://querier.<namespace>.svc.cluster.local:3100
      compress_responses: true

Frontend Service

apiVersion: v1
kind: Service
metadata:
  annotations:
  labels:
    name: query-frontend
  name: query-frontend
  namespace: <namespace>
spec:
  ports:
  - name: query-frontend-http
    port: 3100
    protocol: TCP
    targetPort: 3100
  selector:
    name: query-frontend
  sessionAffinity: None
  type: ClusterIP
  ClusterIP: None
  publishNotReadyAddresses: true

Frontend Deployment

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  labels:
    name: query-frontend
  name: query-frontend
  namespace: <namespace>
spec:
  minReadySeconds: 10
  replicas: 2
  selector:
    matchLabels:
      name: query-frontend
  template:
    metadata:
      labels:
        name: query-frontend
    spec:
      containers:
      - args:
        - -config.file=/etc/loki/config.yaml
        - -log.level=debug
        - -target=query-frontend
        image: grafana/loki:latest
        imagePullPolicy: Always
        name: query-frontend
        ports:
        - containerPort: 3100
          name: http
          protocol: TCP
        resources:
          limits:
            memory: 1200Mi
          requests:
            cpu: "2"
            memory: 600Mi
        volumeMounts:
        - mountPath: /etc/loki
          name: loki-frontend
      restartPolicy: Always
      terminationGracePeriodSeconds: 30
      volumes:
      - configMap:
          defaultMode: 420
          name: loki-frontend
        name: loki-frontend

Grafana

Once you’ve deployed these, point your Grafana data source to the new frontend service. The service is available within the cluster at http://query-frontend.<namespace>.svc.cluster.local:3100.

GRPC Mode (Pull model)

The query frontend operates in one of two ways:

Specify --frontend.downstream-url or its YAML equivalent, frontend.downstream_url. This proxies requests over HTTP to the specified URL.
Without --frontend.downstream-url or its yaml equivalent frontend.downstream_url, the query frontend defaults to a pull service. As a pull service, the frontend instantiates per-tenant queues that downstream queriers pull queries from via GRPC. To act as a pull service, queriers need to specify -querier.frontend-address or its YAML equivalent frontend_worker.frontend_address.
Set ClusterIP=None for the query frontend pull service. This causes DNS resolution of each query frontend pod IP address. It avoids wrongly resolving to the service IP.
Enable publishNotReadyAddresses=true on the query frontend pull service. Doing so eliminates a race condition in which the query frontend address is needed before the query frontend becomes ready when at least one querier connects.