How to Connect to a MySQL Server from a Go Application in Docker When Encountering \"Connection Refused\"?

Error: Connection Refused When Connecting to MySQL Server from Go in Docker

When trying to connect to a MySQL server from a Go application running within Docker, developers may encounter the following error:

dial tcp 127.0.0.1:3306: connect: connection refused

Cause:

By default, Docker containers run in isolated network spaces, making it impossible for applications running within to directly access the host machine's localhost.

Solution:

To resolve this issue, use the special hostname docker.for.mac.localhost instead of localhost. This address enables communication with the host machine's services by employing the Docker networking:

1. Update the connection string in the Go code:

<code class="go">db, err = sql.Open("mysql", dbUser+":"+dbPassword+"@tcp(docker.for.mac.localhost:3306)/"+dbName)</code>

1. If using Docker Compose, add the following line to the docker-compose.yml file under the service definition for the database container:

<code class="yml">ports:
  - "3306:3306"</code>

This will map the host machine's port 3306 to the container's port 3306, allowing the Go application to connect via the correct port.

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