Why Does My Go App Get 'Connection Refused' to Docker Compose Postgres When pgAdmin Connects Successfully?

Docker-Compose Postgres Connection Refused: Resolving Connection Issues

In a docker-compose setup involving Postgres DB with pg-admin and Go, you may encounter connection issues between Go and Postgres, even though pg-admin can successfully connect. This article delves into the potential causes and provides solutions.

Root Cause

The issue arises due to the hostname specified in the database connection URI. While the environment variable points to "postgres," the Docker container/service name for Postgres is "database." This discrepancy prevents Go from establishing a connection.

Solution

There are two possible solutions:

Option 1: Change the Container Name

Modify the Docker compose file to change the service name from "database" to "postgres."

database:
  build: database
  restart: always
  hostname: postgres

Option 2: Use an Explicit Hostname Field

Alternatively, you can add an explicit hostname field to the Postgres service configuration:

database:
  build: database
  restart: always
  hostname: postgres

Either of these solutions will ensure that the hostname in the connection URI matches the Postgres container's name, allowing Go to establish a successful connection.

Additional Considerations

For multiple container services to communicate effectively, you may consider creating a dedicated network. To do this, add a "networks" section to each service you want on the same network.

database:
  # ...

  networks:
    - mynet

backend:
  # ...

  networks:
    - mynet

Finally, define the network at the end of the compose file:

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

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