Unable to connect mysql from docker container? - docker

Question

I have created a docker-compose file it has two services with Go and Mysql. It creates container for go and mysql. Now i am running code which try to connect to mysql database which is running as a docker container. but i get error.
docker-compose.yml
version: "2"
services:
app:
container_name: golang
restart: always
build: .
ports:
- "49160:8800"
links:
- "mysql"
depends_on:
- "mysql"
mysql:
image: mysql
container_name: mysql
volumes:
- dbdata:/var/lib/mysql
restart: always
environment:
- MYSQL_ROOT_PASSWORD=root
- MYSQL_DATABASE=testDB
- MYSQL_USER=root
- MYSQL_PASSWORD=root
ports:
- "3307:3306"
volumes:
dbdata:
Error while connecting to mysql database
golang | 2019/02/28 11:33:05 dial tcp 127.0.0.1:3306: connect: connection refused
golang | 2019/02/28 11:33:05 http: panic serving 172.24.0.1:49066: dial tcp 127.0.0.1:3306: connect: connection refused
golang | goroutine 19 [running]:
Connection with MySql Database
func DB() *gorm.DB {
db, err := gorm.Open("mysql", "root:root#tcp(mysql:3306)/testDB?charset=utf8&parseTime=True&loc=Local")
if err != nil {
log.Panic(err)
}
log.Println("Connection Established")
return db
}
EDIT:Updated docker file
FROM golang:latest
RUN go get -u github.com/gorilla/mux
RUN go get -u github.com/jinzhu/gorm
RUN go get -u github.com/go-sql-driver/mysql
COPY ./wait-for-it.sh .
RUN chmod +x /wait-for-it.sh
WORKDIR /go/src/app
ADD . src
EXPOSE 8800
CMD ["go", "run", "src/main.go"]
I am using gorm package which lets me connet to the database

Answer 1

depends_on is not a verification that MySQL is actually ready to receive connections. It will start the second container once the database container is running regardless it was ready for connections or not which could lead to such an issue with your application as it expects the database to be ready which might not be true.
Quoted from the documentation:
depends_on does not wait for db and redis to be “ready” before starting web - only until they have been started.
There are many tools/scripts that can be used to solve this issue like wait-for which sh compatible in case your image based on Alpine for example (You can use wait-for-it if you have bash in your image)
All you have to do is to add the script to your image through Dockerfile then use this command in docker-compose.yml for the service that you want to make it wait for the database.
What comes after -- is the command that you would normally use to start your application
version: "2"
services:
app:
container_name: golang
...
command: ["./wait-for", "mysql:3306", "--", "go", "run", "myapplication"]
links:
- "mysql"
depends_on:
- "mysql"
mysql:
image: mysql
...
I have removed some parts from the docker-compose for easier readability.
Modify this part go run myapplication with the CMD of your golang image.
See Controlling startup order for more on this problem and strategies for solving it.
Another issue that will rise after you solve the connection issue will be as the following:
Setting MYSQL_USER with root value will cause a failure in MySQL with this error message:
ERROR 1396 (HY000) at line 1: Operation CREATE USER failed for 'root'#'%'
This is because this user already exist in the database and it tries to create another. if you need to use the root user itself you can use only this variable MYSQL_ROOT_PASSWORD or change the value of MYSQL_USER so you can securely use it in your application instead of the root user.
Update: In case you are getting not found and the path was correct, you might need to write the command as below:
command: sh -c "./wait-for mysql:3306 -- go run myapplication"

Answer 2

First, if you are using latest version of docker compose you don't need the link argument in you app service. I quote the docker compose documentation Warning: The --link flag is a legacy feature of Docker. It may eventually be removed. Unless you absolutely need to continue using it, https://docs.docker.com/compose/compose-file/#links
I think the solution is to use the networks argument. This create a docker network and add each service to it.
Try this
version: "2"
services:
app:
container_name: golang
restart: always
build: .
ports:
- "49160:8800"
networks:
- my_network
depends_on:
- "mysql"
mysql:
image: mysql
container_name: mysql
volumes:
- dbdata:/var/lib/mysql
restart: always
networks:
- my_network
environment:
- MYSQL_ROOT_PASSWORD=root
- MYSQL_DATABASE=testDB
- MYSQL_USER=root
- MYSQL_PASSWORD=root
ports:
- "3307:3306"
volumes:
dbdata:
networks:
my_network:
driver: bridge
By the way, if you only connect to Mysql from your app service you don't need to expose the mysql port. If the containers runs in the same network they can reach all ports inside this network.
If my example doesn't works try this
run the docker compose and next go into the app container using
docker container exec -it CONTAINER_NAME bash
Install ping in order to test connection and then run ping mysql.