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Promtail multiline does not merge stacktrace

12/17/2021

Promtail, Grafana, Loki version is 2.4.1. running is Kubernetes.

I was following the documentation.

The exception in the log matches the regular expression. (ZeroWidthSpace is at the beginning of a log line)
multiline stage is set see the attached configuration (promtail.yaml)

I was expecting that error stacktrace will be in a single entry in grafana/loki but every line is a separate entry. Am I missing some configs?

# cat /etc/promtail/promtail.yaml 
server:
  log_level: info
  http_listen_port: 3101

client:
  url: http://***-loki:3100/loki/api/v1/push
  

positions:
  filename: /run/promtail/positions.yaml

scrape_configs:
  # See also https://github.com/grafana/loki/blob/master/production/ksonnet/promtail/scrape_config.libsonnet for reference
  - job_name: kubernetes-pods
    pipeline_stages:
      - multiline:
          firstline: ^\x{200B}\[
          max_lines: 128
          max_wait_time: 3s
    kubernetes_sd_configs:
      - role: pod
    relabel_configs:
      - source_labels:
          - __meta_kubernetes_pod_controller_name
        regex: ([0-9a-z-.]+?)(-[0-9a-f]{8,10})?
        action: replace
        target_label: __tmp_controller_name
      - source_labels:
          - __meta_kubernetes_pod_label_app_kubernetes_io_name
          - __meta_kubernetes_pod_label_app
          - __tmp_controller_name
          - __meta_kubernetes_pod_name
        regex: ^;*([^;]+)(;.*)?$
        action: replace
        target_label: app
      - source_labels:
          - __meta_kubernetes_pod_label_app_kubernetes_io_component
          - __meta_kubernetes_pod_label_component
        regex: ^;*([^;]+)(;.*)?$
        action: replace
        target_label: component
      - action: replace
        source_labels:
        - __meta_kubernetes_pod_node_name
        target_label: node_name
      - action: replace
        source_labels:
        - __meta_kubernetes_namespace
        target_label: namespace
      - action: replace
        replacement: $1
        separator: /
        source_labels:
        - namespace
        - app
        target_label: job
      - action: replace
        source_labels:
        - __meta_kubernetes_pod_name
        target_label: pod
      - action: replace
        source_labels:
        - __meta_kubernetes_pod_container_name
        target_label: container
      - action: replace
        replacement: /var/log/pods/*$1/*.log
        separator: /
        source_labels:
        - __meta_kubernetes_pod_uid
        - __meta_kubernetes_pod_container_name
        target_label: __path__
      - action: replace
        regex: true/(.*)
        replacement: /var/log/pods/*$1/*.log
        separator: /
        source_labels:
        - __meta_kubernetes_pod_annotationpresent_kubernetes_io_config_hash
        - __meta_kubernetes_pod_annotation_kubernetes_io_config_hash
        - __meta_kubernetes_pod_container_name
        target_label: __path__

-- balint.steinbach

grafana

grafana-loki

kubernetes

logging

promtail

1 Answer

12/17/2021

It turned out that the logs look different than what we see in lens pod logs or kubectl logs {pod}.

The original logs consumed by promtail can be found on the host machine:

minikube ssh
cat /var/log/pods/{namespace}_{pod}/{container}/0.log

They look something like this:

{"log":"[default-nioEventLoopGroup-1-1] INFO  HTTP_ACCESS_LOGGER - \"GET /health/readiness HTTP/1.1\" 200 523\n","stream":"stdout","time":"2021-12-17T12:26:29.702621198Z"}

So, the firstline regexp did not match any log line. Unfortunatly, there are no errors about this in the promtail logs.

This is the docker log format and there is a pipeline stage to parse this:

- docker: {}

Additionally there was an issue in the logs. There were extra line breaks in the multi line stacktrace, so this additional pipeline stage filters them:

- replace:
   expression: '(\n)'
   replace: ''

So my working config looks like this:

server:
  log_level: info
  http_listen_port: 3101

client:
  url: http://***-loki:3100/loki/api/v1/push
  

positions:
  filename: /run/promtail/positions.yaml

scrape_configs:
  # See also https://github.com/grafana/loki/blob/master/production/ksonnet/promtail/scrape_config.libsonnet for reference
  - job_name: kubernetes-pods
    pipeline_stages:
      - docker: {}
      - multiline:
          firstline: ^\x{200B}\[
          max_lines: 128
          max_wait_time: 3s
      - replace:
          expression: (\n)
          replace: ""

#config continues below (not copied)

-- balint.steinbach

Source: StackOverflow

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Promtail multiline does not merge stacktrace

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