PostgreSQL Exporter for docker - Prometheus - postgresql

Question

I have been reading this page for years, and now I need some help.
I m starting to configure Prometheus to collect metrics from Docker Swarm and Docker containers, It works really good with cAdvisor and Node Exporter, but now i m having issues to collect metrics from PostgreSQL docker container. I m using this exporter --> https://github.com/wrouesnel/postgres_exporter
This is the service in docker-compose.yml:
postgresql-exporter:
image: wrouesnel/postgres_exporter
ports:
- 9187:9187
networks:
- backend
environment:
- DATA_SOURCE_NAME=postgresql://example:<password>#localhost:5432/example?sslmode=disable
And this is in prometheus.yml
- job_name: 'postgresql-exporter'
static_configs:
- targets: ['postgresql-exporter:9187']
We have two stacks, one with the db and the other one with the monitoring stack.
Logs in the postgresql service:
monitoring_postgresql-exporter.1.krslcea4hz20#master1.xxx.com | time="2019-11-02T16:12:20Z" level=error msg="Error opening connection to database (postgresql://example:PASSWORD_REMOVED#localhost:5432/example?sslmode=disable): dial tcp 127.0.0.1:5432: connect: connection refused" source="postgres_exporter.go:1403"
monitoring_postgresql-exporter.1.krslcea4hz20#master1.xxx.com | time="2019-11-02T16:12:29Z" level=info msg="Established new database connection to \"localhost:5432\"." source="postgres_exporter.go:814"
monitoring_postgresql-exporter.1.krslcea4hz20#master1.xxx.com | time="2019-11-02T16:12:30Z" level=info msg="Established new database connection to \"localhost:5432\"." source="postgres_exporter.go:814"
monitoring_postgresql-exporter.1.krslcea4hz20#master1.xxx.com | time="2019-11-02T16:12:32Z" level=info msg="Established new database connection to \"localhost:5432\"." source="postgres_exporter.go:814"
monitoring_postgresql-exporter.1.krslcea4hz20#master1.xxx.com | time="2019-11-02T16:12:35Z" level=error msg=**"Error opening connection to database (postgresql://example:PASSWORD_REMOVED#localhost:5432/example?sslmode=disable): dial tcp 127.0.0.1:5432: connect: connection refused" source="postgres_exporter.go:1403"**
But when I look in prometheus targets section, the postresql-exporter endpoint says is "UP"
And when I check the pg_up metric it says 0, no conection.
Any idea of how can I solve this?
Any help will be appreciated, thanks!
EDIT: Here is the config of postgreSQL docker service db:
pg:
image: registry.xxx.com:443/pg:201908221000
environment:
- POSTGRES_DB=example
- POSTGRES_USER=example
- POSTGRES_PASSWORD=example
volumes:
- ./postgres/db_data:/var/lib/postgresql/data
networks:
- allnet
deploy:
mode: replicated
replicas: 1
placement:
constraints: [node.role == manager]
restart_policy:
condition: on-failure
max_attempts: 3
window: 120s
Thanks