docker-compose.yml explain of each section

the docker-compose.yml

This file is the “instruction manual” for Docker to know how to start the services

content:

services:
  prometheus:
    image: prom/prometheus:latest
    container_name: prometheus
    ports:
      - "9090:9090"
    volumes:
      -  prometheus.yml:/etc/prometheus/prometheus.yml
      - /prometheus_data:/prometheus
    command:
      - '--config.file=/etc/prometheus/prometheus.yml'
      - '--storage.tsdb.path=/prometheus'
    extra_hosts:
      - "host.docker.internal:host-gateway"
    user: "root" # Ayuda con problemas de permisos en los volúmenes de Linux
    restart: unless-stopped

the command to UP the services in containers is (in the same location):

docker-compose up -d

search by service:

docker ps -a --filter "name=prometheus"

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Volumes

Docker containers are “ephemeral”: if you delete them, everything inside disappears. Volumes are bridges between your computer (host) and the container so that the data survives.

• a:b
  • Left: The file you have in your folder
  • where the service expects to find its configuration within the container

example:

prometheus.yml:/etc/prometheus/prometheus.yml

• Left: The file located in your ~/grafanaandprometheus folder
• Right: Where Prometheus expects to find its configuration within the container
• Left: A folder on your actual machine; Docker looks for it in the root of your system, not in your user folder
• Right: Prometheus’ internal database (TSDB)
• Function: This is where the metrics are stored. By mapping it, if the container breaks or you restart it, Prometheus rereads this folder and you recover the entire history

---

Image

Tells Docker to download the latest official version of Prometheus

---

Container_name

A human-like name so that when you run docker ps, it doesn’t assign a random name like nervous_feynman

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command

These are extra commands you give Prometheus when it starts up

• –config.file: You tell it exactly where the .yml file is located
• –storage.tsdb.path: You confirm that it should save everything in /prometheus (which is the volume we mounted earlier)

---

extra_hosts

host.docker.internal:host-gateway

Because Prometheus runs within an isolated Docker network, it doesn’t know what “localhost” is.

This line tells Prometheus that host.docker.internal is the IP address of your actual server so it can retrieve metrics from your Spring Boot app

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user: "root" and restart

User: On Linux, Prometheus sometimes doesn’t have permission to write to your user’s folders. By using root, you avoid “Permission Denied” errors when trying to create the database

Restart: If the server restarts or the process fails, Docker automatically restarts it