Why Does My Go Application Get a 'Connection Refused' Error When Connecting to a Docker Compose Postgres Database?

Docker Compose Postgres Connection Refusal

Problem:

When attempting to establish a database connection from Go to a Postgres database running on Docker Compose, the error "dial tcp 127.0.0.1:5432: connect: connection refused" occurs.

Solution:

The issue stems from incorrect hostname referencing in the connection string.

Hostname Referencing:

The database hostname is referenced as "postgres" in the "POSTGRES_HOST" environment variable. However, the container/service name for the database in the docker-compose file is "database."

Resolution:

To resolve the issue, there are two options:

1. Change the container/service name: In the docker-compose file, change the "database" service name to "postgres."
2. Add an explicit hostname: Add an "hostname" field to the "database" service in the docker-compose file, explicitly setting it to "postgres."

Network Configuration (Optional):

For improved isolation and communication between services, it is recommended to create a dedicated network for database and application containers. To do this:

1. Add a "networks" configuration to each service that should use the shared network.
2. Define the network at the end of the docker-compose file with a name and optional options.

Example:

database:
  # ...

  networks:
    - mynet

backend:
  # ...

  networks:
    - mynet

networks:
  mynet:
    name: my-shared-db-network

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