Workshop – Accessing log data with Loki
LogQL
Loki supports complex queries through (potentially) terabytes worth of logs.
You can compose your own queries using the LogQL query language, which is a modified version of the Prometheus language (PromQL). LogQL might look complicated at first, but you'll soon discover that it is basically a glorified grep.
LogQL queries consist of two parts:
- a log stream selector
- a log pipeline
Start by selecting one or more streams, and then apply a pipeline operator specifying the string you're looking for. For example, you might want to look for all accesses coming from a specific IP address:
{job="apache"} |= "172.17.0.1"
Or you might be interested in entries related to a specific page:
{job="apache"} |= "cron.php"
The following query defines the exact file you wish to search, loosely looking for Firefox accesses through regexp syntax:
{job="apache",filename="/somelogsdir/access.log"} |~ "Firefox.*"
You can also elect not to filter specific strings. For instance, if you wish to exclude entries with an http 200 status code from the result, use the `
character to delimit the search string:
{job="apache"} != `HTTP/1.1\" 200`
LogQL also provides a way to parse specific log formats (like JSON and logfmt) using a log parser. This option won't be useful in the case of Apache logs, but you'll find great documentation on the topic in the Loki wiki [3].
Grafana and Visualization
You can display the log data in a visually meaningful form using Grafana. To speed things up, I'll deploy Grafana through the official Docker image. I will make sure to run it in host network mode so a connection to Loki is possible:
docker run -d --network host grafana/grafana
Once Grafana is up, use your browser to land on http://localhost:3000. Set up the default admin credentials, click on Configuration | Data Sources, and finally, select Add Data Source.
Select Loki as data source type and enter http://localhost:3100
as the HTTP URL parameter (Figure 1) .
The Save & Test button will make sure settings are validated. You can finally move to the Explore tab, where you can freely query any data source (Figure 2). Once the query is entered and verified, share a short link with coworkers by clicking on the Share icon in the upper part of the page (again Figure 2).
Conclusions
Loki lets you set up a complete log aggregation infrastructure in a very short time span, without having to write a single line of code (see the box entitled "Loki vs Elasticsearch"). All components can run inside a Docker container or in a Kubernetes cluster when it's time to deploy Loki as a production application.
Loki vs Elasticsearch
In the log aggregation ecosystem, Elasticsearch (and, in general, the ELK stack) is certainly a popular choice, but in my opinion, Loki might be better for certain use cases. I give the advantage to Loki for:
- Scalability: Although Elasticsearch indexes all elements of log entries beforehand, Loki specializes in brute force text searches. Loki data is stored unstructured, meaning that Loki can handle a larger amount of data compared to Elasticsearch.
- Metrics format: Loki stores logs with the same structure logic as Prometheus TSDB (streams). This approach means that an application stack (Grafana, Prometheus, and Loki) can pinpoint an application issue starting from a metric or the other way around.
The Loki project has a comparison page for your consideration [4]. Always choose the best tool for your use case.
Loki also supports third-party storage for its logs collection (such as AWS S3 or Apache Cassandra). Next time you deploy a machine or a service, install a Promtail agent and give Loki a try. You'll be surprised by how quickly you can get productive.
Infos
- Loki: https://grafana.com/oss/loki/
- Promtail: https://grafana.com/docs/loki/latest/clients/promtail/
- LogQL Reference: https://grafana.com/docs/loki/latest/logql/
- Loki vs Elasticsearch: https://grafana.com/docs/loki/latest/overview/comparisons/
« Previous 1 2
Buy this article as PDF
(incl. VAT)
Buy Linux Magazine
Direct Download
Read full article as PDF:
Price $2.95
News
-
KaOS 2022.06 Now Available With KDE Plasma 5.25
The newest iteration of KaOS Linux not only adds the latest KDE Plasma desktop but sets LibreOffice as the default.
-
Manjaro 21.3.0 Is Now Available
Manjaro “Ruah” has been released and includes the latest Calamares installer, GNOME 42, and much more.
-
SpiralLinux is a New Linux Distribution Focused on Simplicity
A new Linux distribution, from the creator of GeckoLinux, is a Debian-based operating system with a focus on simplicity and ease of use.
-
HP Dev One Linux Laptop is Now Available for Pre-Order
The System76/HP collaboration Dev One laptop, geared toward developers, is now available for pre-order.
-
NixOS 22.5 Is Now Available
The latest release of NixOS with a much-improved package manager and a user-friendly graphical installer.
-
System76 Teams up with HP to Create the Dev One Laptop
HP and System76 have come together to develop a new laptop, powered by Pop!_OS and aimed toward developers.
-
Titan Linux is a New KDE Linux Based on Debian Stable
Titan Linux is a new Debian-based Linux distribution that features the KDE Plasma desktop with a focus on usability and performance.
-
Danielle Foré Has an Update for elementary OS 7
Now that Ubuntu 22.04 has been released, the team behind elementary OS is preparing for the upcoming 7.0 release.
-
Linux New Media Launches Open Source JobHub
New job website focuses on connecting technical and non-technical professionals with organizations in open source.
-
Ubuntu Cinnamon 22.04 Now Available
Ubuntu Cinnamon 22.04 has been released with all the additions from upstream as well as other features and improvements.