How to set environment variables in Phoenix with Distillery library? - environment-variables

Question

Follow this guide to use Distillery to release a elixir/phoenix project:
https://blog.polyscribe.io/a-complete-guide-to-deploying-elixir-phoenix-applications-on-kubernetes-part-1-setting-up-d88b35b64dcd
At the set config/prod.exs step, the author wrote:
config :myapp, Myapp.Repo,
adapter: Ecto.Adapters.Postgres,
hostname: "${DB_HOSTNAME}",
username: "${DB_USERNAME}",
password: "${DB_PASSWORD}",
database: "${DB_NAME}",
to config database. Here using ${DB_HOSTNAME} type to get environment variables, but not System.get_env("DB_HOSTNAME").
However, when I run MIX_ENV=prod mix release --env=prod and set environment variables local:
REPLACE_OS_VARS=true PORT=4000 HOST=0.0.0.0 SECRET_KEY_BASE=highlysecretkey DB_USERNAME=postgres DB_PASSWORD=postgres DB_NAME=myapp_dev DB_HOSTNAME=localhost ./_build/prod/rel/myapp/bin/myapp foreground
It loops:
12:05:13.671 [error] Postgrex.Protocol (#PID<0.1348.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (${DB_HOSTNAME}:5432): non-existing domain - :nxdomain
12:05:13.671 [error] Postgrex.Protocol (#PID<0.1347.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (${DB_HOSTNAME}:5432): non-existing domain - :nxdomain
12:05:13.672 [error] Postgrex.Protocol (#PID<0.1344.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (${DB_HOSTNAME}:5432): non-existing domain - :nxdomain
12:05:13.672 [error] Postgrex.Protocol (#PID<0.1346.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (${DB_HOSTNAME}:5432): non-existing domain - :nxdomain
...
It seems ${DB_HOSTNAME} didn't been known by elixir/phoenix.
I am using Elixir 1.5.2 and Phoenix 1.3 now. The version problem?

Answer 1

I never saw this approach and I am unsure how it is supposed to work. The common way to getting the environment variables at runtime would be:
{:system, "VAR"}
For your case it’d be:
config :myapp, Myapp.Repo,
adapter: Ecto.Adapters.Postgres,
hostname: {:system, "DB_HOSTNAME"},
username: {:system, "DB_USERNAME"},
password: {:system, "DB_PASSWORD"},
database: {:system, "DB_NAME"}