mysqld: dial tcp 127.0.0.1:3306: connect: connection refused - mysql

Question

I'm trying to dockerize monitoring of mysql using prom/mysqld-exporter and prom/prometheus. I have configured the docker-compose.yml file like the following:
version: '3'
services:
mysql:
image: mysql
container_name: mysql
restart: always
volumes:
- mysql:/var/lib/mysql
# command:
# - CREATE USER 'root'#'localhost' IDENTIFIED BY 'password' WITH MAX_USER_CONNECTIONS 3;
# - GRANT PROCESS, REPLICATION CLIENT, SELECT ON *.* TO 'root'#'localhost';
environment:
- MYSQL_ROOT_PASSWORD= password
- MYSQL_DATABASE= db #Defining a new Database
- MYSQL_USER= mostafa
- MYSQL_PASSWORD= ghadimi
ports:
- 3306:3306
- 33060:33060
prometheus:
image: prom/prometheus
container_name: prometheus
ports:
- 9090:9090
volumes:
- prometheus:/prometheus
- ./prometheus/prometheus.yml:/etc/prometheus/prometheus.yml
command:
- --config.file=/etc/prometheus/prometheus.yml
mysql-exporter:
image: prom/mysqld-exporter
container_name: mysql-exporter
ports:
- 9104:9104
volumes:
- ./mysql-exporter/.my.cnf:/root/.my.cnf
depends_on:
- mysql
volumes:
mysql:
prometheus:
and here is my ./mysql-exporter/.my.cnf file:
[client]
user=mostafa
password=ghadimi
After running docker-compose up command, everything works properly except the following error!:
mysqld: dial tcp 127.0.0.1:3306: connect: connection refused
I don't know how can I fix it!
PS: I have also tried to connect to mysql through its container and docker exec -it <container-id> bash command and I have attempted all the possible passwords (like empty string and the password I have set in docker-compose file), but I face with another error:
ERROR 1045 (28000): Access denied for user 'root'#'localhost' (using password: YES)

Answer 1

Mysql-d exporter is looking for mysql instance on localhost, but it is not running on the localhost inside mysqld container. You will have to pass external connection string with the host of mysql because this is the name of mysql service in docker-compose. From mysqld-exporter docs - you will have to pass environment variable to mysqld-exporter container with this datasource connection string :
mysql-exporter:
image: prom/mysqld-exporter
container_name: mysql-exporter
ports:
- 9104:9104
volumes:
- ./mysql-exporter/.my.cnf:/root/.my.cnf
environment:
- DATA_SOURCE_NAME="user:password#mysql:3306/database"
depends_on:
- mysql
And change user, password and database name to your desired ones.