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troubleshooting.md

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Troubleshooting

"Loki: Bad Gateway. 502"

This error can appear in Grafana when you add Loki as a datasource. It means that Grafana cannot connect to Loki. This can have several reasons:

  • If you deploy in docker env, Grafana and Loki are not in same node, check iptables or firewalls to ensure they can connect.
  • If you deploy in kubernetes env, please note:
    • Grafana and Loki are in same namespace, set Loki url as "http://$LOKI_SERVICE_NAME:$LOKI_PORT".
    • Grafana and Loki are in different namespace, set Loki url as "http://$LOKI_SERVICE_NAME.$LOKI_NAMESPACE:$LOKI_PORT".

"Data source connected, but no labels received. Verify that Loki and Promtail is configured properly."

This error can appear in Grafana when you add Loki as a datasource. It means that Grafana can connect to Loki, but Loki has not received any logs from promtail. This can have several reasons:

  • Promtail cannot reach Loki, check promtail's output.
  • Promtail started sending logs before Loki was ready. This can happen in test environments where promtail already read all logs and sent them off. Here is what you can do:
    • Generally start promtail after Loki, e.g., 60 seconds later.
    • Restarting promtail will not necessarily resend log messages that have been read. To force sending all messages again, delete the positions file (default location /tmp/positions.yaml) or make sure new log messages are written after both promtail and Loki have started.
  • Promtail is ignoring targets because of a configuration rule
    • Detect this by turning on debug logging and then look for dropping target, no labels or ignoring target messages.
  • Promtail cannot find the location of your log files. Check that the scrape_configs contains valid path setting for finding the logs in your worker nodes.
  • Your pods are running but not with the labels Promtail is expecting. Check the Promtail scape_configs.

Troubleshooting targets

Promtail offers two pages that you can use to understand how service discovery works. The service discovery page (/service-discovery) shows all discovered targets with their labels before and after relabeling as well as the reason why the target has been dropped. The targets page (/targets) however displays only targets being actively scraped with their respective labels, files and positions.

You can access those two pages by port-forwarding the promtail port (9080 or 3101 via helm) locally:

kubectl port-forward loki-promtail-jrfg7 9080

Debug output

Both binaries support a log level parameter on the command-line, e.g.: loki —log.level= debug ...

Failed to create target, "ioutil.ReadDir: readdirent: not a directory"

The promtail configuration contains a __path__ entry to a directory that promtail cannot find.

Connecting to a promtail pod to troubleshoot

First check Troubleshooting targets section above, if that doesn't help answer your questions you can connect to the promtail pod to further investigate.

In your cluster if you are running promtail as a daemonset, you will have a promtail pod on each node, to figure out which promtail you want run:

$ kubectl get pods --all-namespaces -o wide
NAME                                   READY   STATUS    RESTARTS   AGE   IP             NODE        NOMINATED NODE
...
nginx-7b6fb56fb8-cw2cm                 1/1     Running   0          41d   10.56.4.12     node-ckgc   <none>
...
promtail-bth9q                         1/1     Running   0          3h    10.56.4.217    node-ckgc   <none>

That output is truncated to highlight just the two pods we are interseted in, you can see with the -o wide flag the NODE on which they are running.

You'll want to match the node for the pod you are interested in, in this example nginx, to the promtail running on the same node.

To debug you can connect to the promtail pod:

kubectl exec -it promtail-bth9q -- /bin/ash

Once connected, verify the config in /etc/promtail/promtail.yml is what you expected

Also check /var/log/positions.yaml and make sure promtail is tailing the logs you would expect

You can check the promtail log by looking in /var/log/containers at the promtail container log

Enable tracing for loki

We support (jaeger)[https://www.jaegertracing.io/] to trace loki, just add env JAEGER_AGENT_HOST to where loki run, and you can use jaeger to trace.

If you deploy with helm, refer to following command:

$ helm upgrade --install loki loki/loki --set "loki.jaegerAgentHost=YOUR_JAEGER_AGENT_HOST"