Logging With Docker, Promtail and Grafana Loki

3 min readNov 18, 2022

In this post we will use Grafana Promtail to collect all our logs and ship it to Grafana Loki.

About

We will be using Docker Compose and mount the docker socket to Grafana Promtail so that it is aware of all the docker events and configure it that only containers with docker labels logging=promtail needs to be enabled for logging, which will then scrape those logs and send it to Grafana Loki where we will visualize it in Grafana.

Promtail

In our promtail configuration config/promtail.yaml:

# https://grafana.com/docs/loki/latest/clients/promtail/configuration/
# https://docs.docker.com/engine/api/v1.41/#operation/ContainerList
server:
  http_listen_port: 9080
  grpc_listen_port: 0

positions:
  filename: /tmp/positions.yaml

clients:
  - url: http://loki:3100/loki/api/v1/push

scrape_configs:
  - job_name: flog_scrape
    docker_sd_configs:
      - host: unix:///var/run/docker.sock
        refresh_interval: 5s
        filters:
          - name: label
            values: ["logging=promtail"]
    relabel_configs:
      - source_labels: ['__meta_docker_container_name']
        regex: '/(.*)'
        target_label: 'container'
      - source_labels: ['__meta_docker_container_log_stream']
        target_label: 'logstream'
      - source_labels: ['__meta_docker_container_label_logging_jobname']
        target_label: 'job'

You can see we are using the docker_sd_configs provider and filter only docker containers with the docker labels logging=promtail and once we have those logs we relabel our labels to have the container name and we also use docker labels like log_stream and logging_jobname to add labels to our logs.

Grafana Config

We would like to auto configure our datasources for Grafana and in config/grafana-datasources.yml we have:

apiVersion: 1

datasources:
  - name: Loki
    type: loki
    access: proxy
    url: http://loki:3100
    version: 1
    editable: false
    isDefault: true

Docker Compose

Then lastly we have our docker-compose.yml that wire up all our containers:

version: '3.8'

services:
  nginx-app:
    container_name: nginx-app
    image: nginx
    labels:
      logging: "promtail"
      logging_jobname: "containerlogs"
    ports:
      - 8080:80
    networks:
      - app

  grafana:
    image: grafana/grafana:latest
    ports:
      - 3000:3000
    volumes:
      - ./config/grafana-datasources.yml:/etc/grafana/provisioning/datasources/datasources.yaml
    environment:
      - GF_AUTH_ANONYMOUS_ENABLED=true
      - GF_AUTH_ANONYMOUS_ORG_ROLE=Admin
      - GF_AUTH_DISABLE_LOGIN_FORM=true
    networks:
      - app

  loki:
    image: grafana/loki:latest
    ports:
      - 3100:3100
    command: -config.file=/etc/loki/local-config.yaml
    networks:
      - app

  promtail:
    image:  grafana/promtail:latest
    container_name: promtail
    volumes:
      - ./config/promtail.yaml:/etc/promtail/docker-config.yaml
      - /var/lib/docker/containers:/var/lib/docker/containers:ro
      - /var/run/docker.sock:/var/run/docker.sock
    command: -config.file=/etc/promtail/docker-config.yaml
    depends_on:
      - loki
    networks:
      - app

networks:
  app:
    name: app

As you can see with our nginx container we define our labels:

  nginx-app:
    container_name: nginx-app
    image: nginx
    labels:
      logging: "promtail"
      logging_jobname: "containerlogs"

Which uses logging: "promtail" to let promtail know this log container’s log to be scraped and logging_jobname: "containerlogs" which will assign containerlogs to the job label.