Prometheus - Target Connection refused - docker

Question

I'm trying to get a Prometheus container to scrape metrics from cAdvisor.
This is my prometheus.yml:
global:
scrape_interval: 10s
evaluation_interval: 10s
scrape_configs:
- job_name: "prometheus"
static_configs:
- targets: ["localhost:9090"]
- job_name: "docker"
static_configs:
- targets: ['localhost:9323']
- job_name: "cadvisor"
scrape_interval: 5s
static_configs:
- targets: ['localhost:7070']
labels:
alias: "cadvisor"
And my docker-compose.yml:
version: "3.5"
services:
app:
container_name: app
build: "./app"
restart: always
volumes:
- ./app:/app
depends_on:
- db
links:
- db
ports:
- 8080:8080
db:
container_name: db
image: postgres
restart: always
volumes:
- ./data/postgres:/var/lib/postgresql/data
environment:
- POSTGRES_DB=articlesdb
- POSTGRES_USER=dbuser
- POSTGRES_PASSWORD=dbpassword
ports:
- "5432:5432"
prometheus:
container_name: prometheus
image: prom/prometheus:latest
#build:
# context: ./prometheus
# dockerfile: Dockerfile
ports:
- 9090:9090
volumes:
- ./prometheus/prometheus.yml:/etc/prometheus/prometheus.yml
command:
- '--config.file=/etc/prometheus/prometheus.yml'
depends_on:
- cadvisor
cadvisor:
image: google/cadvisor:latest
container_name: cadvisor
ports:
- 7070:8080
volumes:
- /:/rootfs:ro
- /var/run:/var/run:rw
- /sys:/sys:ro
- /var/lib/docker/:/var/lib/docker:ro
depends_on:
- db
In the targets section Prometheus says that the connection to the cAdvisor container and Docker daemon is refused, while Prometheus' to itself works.
I can reach cAdvisor at localhost:7070/metrics with either cURL or on my browser. What could be the issue, and how can I fix it?

Answer 1

In your docker-compose file you named the cAdvisor service ‘cadvisor’ so in the docker network it can be accessed via the DNS name cadvisor. Change your prometheus.yml static_config like this to scrape the service:
- job_name: "cadvisor"
scrape_interval: 5s
static_configs:
- targets: ['cadvisor:7070']
labels:
alias: "cadvisor"