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Using Grafana to Query your logs

To query and display your logs you need to configure your Loki to be a datasource in your Grafana.

Note: Querying your logs without Grafana is possible by using logcli.

Configuring the Loki Datasource in Grafana

Grafana ships with built-in support for Loki as part of its latest release (6.0).

  1. Log into your Grafana, e.g, http://localhost:3000 (default username: admin, default password: admin)
  2. Go to Configuration > Data Sources via the cog icon on the left side bar.
  3. Click the big + Add data source button.
  4. Choose Loki from the list.
  5. The http URL field should be the address of your Loki server e.g. http://localhost:3100 when running locally or with docker, http://loki:3100 when running with docker-compose or kubernetes.
  6. To see the logs, click "Explore" on the sidebar, select the Loki datasource, and then choose a log stream using the "Log labels" button.

Read more about the Explore feature in the Grafana docs and on how to search and filter logs with Loki.

To configure the datasource via provisioning see Configuring Grafana via Provisioning and make sure to adjust the URL similarly as shown above.

Searching with Labels and Distributed Grep

A log query consists of two parts: log stream selector, and a filter expression. For performance reasons you need to start by choosing a set of log streams using a Prometheus-style log stream selector.

The log stream selector will reduce the number of log streams to a manageable volume and then the regex search expression is used to do a distributed grep over those log streams.

Log Stream Selector

For the label part of the query expression, wrap it in curly braces {} and then use the key value syntax for selecting labels. Multiple label expressions are separated by a comma:

{app="mysql",name="mysql-backup"}

The following label matching operators are currently supported:

  • = exactly equal.
  • != not equal.
  • =~ regex-match.
  • !~ do not regex-match.

Examples:

  • {name=~"mysql.+"}
  • {name!~"mysql.+"}

The same rules that apply for Prometheus Label Selectors apply for Loki Log Stream Selectors.

Filter Expression

After writing the Log Stream Selector, you can filter the results further by writing a search expression. The search expression can be just text or a regex expression.

Example queries:

  • {job="mysql"} |= "error"
  • {name="kafka"} |~ "tsdb-ops.*io:2003"
  • {instance=~"kafka-[23]",name="kafka"} != kafka.server:type=ReplicaManager

Filter operators can be chained and will sequentially filter down the expression - resulting log lines will satisfy every filter. Eg:

{job="mysql"} |= "error" != "timeout"

The following filter types have been implemented:

  • |= line contains string.
  • != line does not contain string.
  • |~ line matches regular expression.
  • !~ line does not match regular expression.

The regex expression accepts RE2 syntax. The matching is case-sensitive by default and can be switched to case-insensitive prefixing the regex with (?i).

Query Language Extensions

The query language is still under development to support more features, e.g.,:

  • AND / NOT operators
  • Number extraction for timeseries based on number in log messages
  • JSON accessors for filtering of JSON-structured logs
  • Context (like grep -C n)
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