docker-compose mongodb phoenix, [error] failed to connect: ** (Mongo.Error) tcp connect: connection refused - :econnrefused

https://docs.docker.com/compose/compose-file/#depends_on explicitly says:

There are several things to be aware of when using depends_on:

• depends_on does not wait for db and redis to be “ready” before starting web - only until they have been started. If you need to wait for a service to be ready,

and advises you to implement the logic to wait for mongodb to spinup and be ready to accept connections by yourself: https://docs.docker.com/compose/startup-order/

In your case it could be something like:

CMD wait-for-db.sh && mix phx.server

where wait-for-db.sh can be as simple as

#!/bin/bashuntil nc -z localhost 27017; do echo "waiting for db"; sleep 1; done

for which you need nc and wait-for-db.sh installed in the container.

There are plenty of other alternative tools to test if db container is listening on the target port.

UPDATE:

The network connection between containers is described at https://docs.docker.com/compose/networking/:

When you run docker-compose up, the following happens:

• A network called myapp_default is created, where myapp is name of the directory where docker-compose.yml is stored.
• A container is created using phoenix’s configuration. It joins the network myapp_default under the name phoenix.
• A container is created using db’s configuration. It joins the network myapp_default under the name db.

Each container can now look up the hostname phoenix or db and get back the appropriate container’s IP address. For example, phoenix’s application code could connect to the URL mongodb://db:27017 and start using the Mongodb database.

It was an issue with my dev environment not connecting to the mongodb url specified in docker-compose. Instead of localhost, it should be db as named in my docker-compose.yml file

For clarity to dev env:

• modify config/dev.exs to (replace with correct vars)

  username: System.get_env("PGUSER"),  password: System.get_env("PGPASSWORD"),  database: System.get_env("PGDATABASE"),  hostname: System.get_env("PGHOST"),  port:     System.get_env("PGPORT"),

• create a dot env file on the root folder of your project (replace with relevant vars to the db service used)

PGUSER=some_userPGPASSWORD=some_passwordPGDATABASE=some_databasePGPORT=5432PGHOST=db

Note that we have added port.
Host can be localhost but should be mongodb or db or even url when working on a docker-compose or server or k8s.

will update answer for prod config...