Not able to connect to mysql running in a container from application - mysql

Question

I am trying to run SLTs and for that i have defined mysql as a dependency in my docker-compose.yml
Platform:
networks:
- shared
image: platform
build:
context: ../../../
dockerfile: Dockerfile.slt
container_name: platform
ports:
- 7777:7777
- 1053:1053
volumes:
- /tmp/server:/tmp/server
restart: unless-stopped
env_file:
- docker.env
depends_on:
- predictiondb
predictiondb:
networks:
- shared
image: mysql:latest
restart: always
container_name: predictiondb
environment:
# Password for root access
MYSQL_ROOT_PASSWORD: "root"
MYSQL_DATABASE: "prediction"
ports:
- 3306:3306
expose:
- 3306
volumes:
- predictiondb:/var/lib/mysql
After running the docker-compose.yml i am trying to connect with the mysql using my application.
import (
"database/sql"
_ "github.com/go-sql-driver/mysql"
)
func main() {
db, err := sql.Open("mysql", "root:root#tcp(localhost:3306)/prediction")
if err != nil {
panic(err)
}
defer db.Close()
err = db.ping()
if err != nil {
log.Print(err)
}
Here i am getting the error
{"error": "dial tcp 172.18.0.2:3306: connect: connection refused"}
I have checked that mysql is running in a container using docker ps command.
I have tried connecting with mysql from my local(mysql -P 3306 --protocol=tcp -u root -p) on the port 3306 and able to connect and also able to see the prediction database created.
checked the logs of the container and mysql is running.
tried using root:root#tcp(predictiondb:3306)/prediction, but still same error.
mysql docker logs
2022-07-20T15:49:26.367485Z 11 [System] [MY-013172] [Server] Received SHUTDOWN from user root. Shutting down mysqld (Version: 8.0.29).
2022-07-20T15:49:27.706467Z 0 [System] [MY-010910] [Server] /usr/sbin/mysqld: Shutdown complete (mysqld 8.0.29) MySQL Community Server - GPL.
2022-07-20 15:49:28+00:00 [Note] [Entrypoint]: Temporary server stopped
2022-07-20 15:49:28+00:00 [Note] [Entrypoint]: MySQL init process done. Ready for start up.
2022-07-20T15:49:28.598959Z 0 [System] [MY-010116] [Server] /usr/sbin/mysqld (mysqld 8.0.29) starting as process 1
2022-07-20T15:49:28.606127Z 1 [System] [MY-013576] [InnoDB] InnoDB initialization has started.
2022-07-20T15:49:28.712782Z 1 [System] [MY-013577] [InnoDB] InnoDB initialization has ended.
2022-07-20T15:49:28.928948Z 0 [Warning] [MY-010068] [Server] CA certificate ca.pem is self signed.
2022-07-20T15:49:28.929033Z 0 [System] [MY-013602] [Server] Channel mysql_main configured to support TLS. Encrypted connections are now supported for this channel.
2022-07-20T15:49:28.931482Z 0 [Warning] [MY-011810] [Server] Insecure configuration for --pid-file: Location '/var/run/mysqld' in the path is accessible to all OS users. Consider choosing a different directory.
2022-07-20T15:49:28.972456Z 0 [System] [MY-011323] [Server] X Plugin ready for connections. Bind-address: '::' port: 33060, socket: /var/run/mysqld/mysqlx.sock
2022-07-20T15:49:28.972721Z 0 [System] [MY-010931] [Server] /usr/sbin/mysqld: ready for connections. Version: '8.0.29' socket: '/var/run/mysqld/mysqld.sock' port: 3306 MySQL Community Server - GPL.
My application is running in another docker container, i am using same docker-compose.yml
Any help will be appreciated.

Answer 1

When your application is running in a container started by the same docker-compose file you cannot access the exposed port from localhost because it is visible only from the host, it cannot be accessed from another container. You need to connect to the wanted application through the container name:
db, err := sql.Open("mysql", "root:root#tcp(predictiondb:3306)/prediction")