query-frontend does not support websockets/tailing

[gcotone]

Describe the bug
When running loki with query-frontend, live tailing is not possible since the frontend component does not support websockets.
Probably something for the backlog.

To Reproduce
Steps to reproduce the behavior:

1. Started Loki 2.0.0
2. Started Promtail 2.0.0-amd64
3. Query frontend configured as datasource in Grafana
4. Live tail: {host="HOSTNAME"}

Expected behavior
Live tailing should be supported on the query-frontend, or referenced as unsupported in the documentation. The issue is not seen when configuring directly the queriers as endpoints on the Grafana loki datasource.

Environment:

• Infrastructure: kubernetes
• Deployment tool: N/A

Screenshots, Promtail config, or terminal output
The following error messages are seen on the loki-query-frontend component while enabling a live log streaming in grafana Explore:

level=warn ts=2020-11-04T16:19:15.449576459Z caller=logging.go:60 traceID=13b0c358fdeda1be msg="GET /loki/api/v1/tail?query=%7Bhost%3D%22HOSTNAME%22%7D 319.174371ms, error: http: request method or response status code does not allow body ws: true; Accept-Encoding: gzip, deflate, br; Accept-Language: en-US,en;q=0.9,es-AR;q=0.8,es;q=0.7,de-DE;q=0.6,de;q=0.5; Cache-Control: no-cache; Connection: Upgrade; Pragma: no-cache; Sec-Websocket-Extensions: permessage-deflate; client_max_window_bits; Sec-Websocket-Key: q8fiwvRig1GCV0ENXabwRQ==; Sec-Websocket-Version: 13; Upgrade: websocket; User-Agent: Grafana/7.3.1; X-Amzn-Trace-Id: Root=1-5fa2d483-763afc81414231b346f530ac; X-Forwarded-For: 23.116.65.148, 10.2.6.1, 10.2.6.1; "

Query-frontend configuration

server:
  http_listen_port: 8080

schema_config:
  configs:
  - from: 2020-05-15
    store: aws
    object_store: s3
    schema: v11
    index:
      prefix: loki_index_
      period: 24h
      tags:
        application: app
        component: loki
  - from: 2020-10-29
    store: boltdb-shipper
    object_store: s3
    schema: v11
    index:
      prefix: loki_index_
      period: 24h

query_range:
  align_queries_with_step: true
  max_retries: 5
  split_queries_by_interval: 10m
  cache_results: true

  results_cache:
    cache:
      enable_fifocache: true
      fifocache:
        max_size_bytes: 512MB
        validity: 24h

limits_config:
  max_cache_freshness_per_query: '10m'

frontend:
  log_queries_longer_than: 5s
  downstream_url: http://loki-querier-svc:8080
  compress_responses: true

[zhanghjster]

Try:

frontend:
    tail_proxy_url: http://loki-querier-svc:8080

[gcotone]

it works, thanks!